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   1// SPDX-License-Identifier: GPL-2.0-only
   2#include <linux/kernel.h>
   3#include <linux/errno.h>
   4#include <linux/err.h>
   5#include <linux/spinlock.h>
   6
   7#include <linux/mm.h>
   8#include <linux/memfd.h>
   9#include <linux/memremap.h>
  10#include <linux/pagemap.h>
  11#include <linux/rmap.h>
  12#include <linux/swap.h>
  13#include <linux/swapops.h>
  14#include <linux/secretmem.h>
  15
  16#include <linux/sched/signal.h>
  17#include <linux/rwsem.h>
  18#include <linux/hugetlb.h>
  19#include <linux/migrate.h>
  20#include <linux/mm_inline.h>
  21#include <linux/pagevec.h>
  22#include <linux/sched/mm.h>
  23#include <linux/shmem_fs.h>
  24
  25#include <asm/mmu_context.h>
  26#include <asm/tlbflush.h>
  27
  28#include "internal.h"
  29
  30struct follow_page_context {
  31	struct dev_pagemap *pgmap;
  32	unsigned int page_mask;
  33};
  34
  35static inline void sanity_check_pinned_pages(struct page **pages,
  36					     unsigned long npages)
  37{
  38	if (!IS_ENABLED(CONFIG_DEBUG_VM))
  39		return;
  40
  41	/*
  42	 * We only pin anonymous pages if they are exclusive. Once pinned, we
  43	 * can no longer turn them possibly shared and PageAnonExclusive() will
  44	 * stick around until the page is freed.
  45	 *
  46	 * We'd like to verify that our pinned anonymous pages are still mapped
  47	 * exclusively. The issue with anon THP is that we don't know how
  48	 * they are/were mapped when pinning them. However, for anon
  49	 * THP we can assume that either the given page (PTE-mapped THP) or
  50	 * the head page (PMD-mapped THP) should be PageAnonExclusive(). If
  51	 * neither is the case, there is certainly something wrong.
  52	 */
  53	for (; npages; npages--, pages++) {
  54		struct page *page = *pages;
  55		struct folio *folio;
  56
  57		if (!page)
  58			continue;
  59
  60		folio = page_folio(page);
  61
  62		if (is_zero_page(page) ||
  63		    !folio_test_anon(folio))
  64			continue;
  65		if (!folio_test_large(folio) || folio_test_hugetlb(folio))
  66			VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page), page);
  67		else
  68			/* Either a PTE-mapped or a PMD-mapped THP. */
  69			VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page) &&
  70				       !PageAnonExclusive(page), page);
  71	}
  72}
  73
  74/*
  75 * Return the folio with ref appropriately incremented,
  76 * or NULL if that failed.
  77 */
  78static inline struct folio *try_get_folio(struct page *page, int refs)
  79{
  80	struct folio *folio;
  81
  82retry:
  83	folio = page_folio(page);
  84	if (WARN_ON_ONCE(folio_ref_count(folio) < 0))
  85		return NULL;
  86	if (unlikely(!folio_ref_try_add(folio, refs)))
  87		return NULL;
  88
  89	/*
  90	 * At this point we have a stable reference to the folio; but it
  91	 * could be that between calling page_folio() and the refcount
  92	 * increment, the folio was split, in which case we'd end up
  93	 * holding a reference on a folio that has nothing to do with the page
  94	 * we were given anymore.
  95	 * So now that the folio is stable, recheck that the page still
  96	 * belongs to this folio.
  97	 */
  98	if (unlikely(page_folio(page) != folio)) {
  99		if (!put_devmap_managed_folio_refs(folio, refs))
 100			folio_put_refs(folio, refs);
 101		goto retry;
 102	}
 103
 104	return folio;
 105}
 106
 107static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
 108{
 109	if (flags & FOLL_PIN) {
 110		if (is_zero_folio(folio))
 111			return;
 112		node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs);
 113		if (folio_test_large(folio))
 114			atomic_sub(refs, &folio->_pincount);
 115		else
 116			refs *= GUP_PIN_COUNTING_BIAS;
 117	}
 118
 119	if (!put_devmap_managed_folio_refs(folio, refs))
 120		folio_put_refs(folio, refs);
 121}
 122
 123/**
 124 * try_grab_folio() - add a folio's refcount by a flag-dependent amount
 125 * @folio:    pointer to folio to be grabbed
 126 * @refs:     the value to (effectively) add to the folio's refcount
 127 * @flags:    gup flags: these are the FOLL_* flag values
 128 *
 129 * This might not do anything at all, depending on the flags argument.
 130 *
 131 * "grab" names in this file mean, "look at flags to decide whether to use
 132 * FOLL_PIN or FOLL_GET behavior, when incrementing the folio's refcount.
 133 *
 134 * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
 135 * time.
 136 *
 137 * Return: 0 for success, or if no action was required (if neither FOLL_PIN
 138 * nor FOLL_GET was set, nothing is done). A negative error code for failure:
 139 *
 140 *   -ENOMEM		FOLL_GET or FOLL_PIN was set, but the folio could not
 141 *			be grabbed.
 142 *
 143 * It is called when we have a stable reference for the folio, typically in
 144 * GUP slow path.
 145 */
 146int __must_check try_grab_folio(struct folio *folio, int refs,
 147				unsigned int flags)
 148{
 149	if (WARN_ON_ONCE(folio_ref_count(folio) <= 0))
 150		return -ENOMEM;
 151
 152	if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(&folio->page)))
 153		return -EREMOTEIO;
 154
 155	if (flags & FOLL_GET)
 156		folio_ref_add(folio, refs);
 157	else if (flags & FOLL_PIN) {
 158		/*
 159		 * Don't take a pin on the zero page - it's not going anywhere
 160		 * and it is used in a *lot* of places.
 161		 */
 162		if (is_zero_folio(folio))
 163			return 0;
 164
 165		/*
 166		 * Increment the normal page refcount field at least once,
 167		 * so that the page really is pinned.
 168		 */
 169		if (folio_test_large(folio)) {
 170			folio_ref_add(folio, refs);
 171			atomic_add(refs, &folio->_pincount);
 172		} else {
 173			folio_ref_add(folio, refs * GUP_PIN_COUNTING_BIAS);
 174		}
 175
 176		node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
 177	}
 178
 179	return 0;
 180}
 181
 182/**
 183 * unpin_user_page() - release a dma-pinned page
 184 * @page:            pointer to page to be released
 185 *
 186 * Pages that were pinned via pin_user_pages*() must be released via either
 187 * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so
 188 * that such pages can be separately tracked and uniquely handled. In
 189 * particular, interactions with RDMA and filesystems need special handling.
 190 */
 191void unpin_user_page(struct page *page)
 192{
 193	sanity_check_pinned_pages(&page, 1);
 194	gup_put_folio(page_folio(page), 1, FOLL_PIN);
 195}
 196EXPORT_SYMBOL(unpin_user_page);
 197
 198/**
 199 * unpin_folio() - release a dma-pinned folio
 200 * @folio:         pointer to folio to be released
 201 *
 202 * Folios that were pinned via memfd_pin_folios() or other similar routines
 203 * must be released either using unpin_folio() or unpin_folios().
 204 */
 205void unpin_folio(struct folio *folio)
 206{
 207	gup_put_folio(folio, 1, FOLL_PIN);
 208}
 209EXPORT_SYMBOL_GPL(unpin_folio);
 210
 211/**
 212 * folio_add_pin - Try to get an additional pin on a pinned folio
 213 * @folio: The folio to be pinned
 214 *
 215 * Get an additional pin on a folio we already have a pin on.  Makes no change
 216 * if the folio is a zero_page.
 217 */
 218void folio_add_pin(struct folio *folio)
 219{
 220	if (is_zero_folio(folio))
 221		return;
 222
 223	/*
 224	 * Similar to try_grab_folio(): be sure to *also* increment the normal
 225	 * page refcount field at least once, so that the page really is
 226	 * pinned.
 227	 */
 228	if (folio_test_large(folio)) {
 229		WARN_ON_ONCE(atomic_read(&folio->_pincount) < 1);
 230		folio_ref_inc(folio);
 231		atomic_inc(&folio->_pincount);
 232	} else {
 233		WARN_ON_ONCE(folio_ref_count(folio) < GUP_PIN_COUNTING_BIAS);
 234		folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
 235	}
 236}
 237
 238static inline struct folio *gup_folio_range_next(struct page *start,
 239		unsigned long npages, unsigned long i, unsigned int *ntails)
 240{
 241	struct page *next = nth_page(start, i);
 242	struct folio *folio = page_folio(next);
 243	unsigned int nr = 1;
 244
 245	if (folio_test_large(folio))
 246		nr = min_t(unsigned int, npages - i,
 247			   folio_nr_pages(folio) - folio_page_idx(folio, next));
 248
 249	*ntails = nr;
 250	return folio;
 251}
 252
 253static inline struct folio *gup_folio_next(struct page **list,
 254		unsigned long npages, unsigned long i, unsigned int *ntails)
 255{
 256	struct folio *folio = page_folio(list[i]);
 257	unsigned int nr;
 258
 259	for (nr = i + 1; nr < npages; nr++) {
 260		if (page_folio(list[nr]) != folio)
 261			break;
 262	}
 263
 264	*ntails = nr - i;
 265	return folio;
 266}
 267
 268/**
 269 * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
 270 * @pages:  array of pages to be maybe marked dirty, and definitely released.
 271 * @npages: number of pages in the @pages array.
 272 * @make_dirty: whether to mark the pages dirty
 273 *
 274 * "gup-pinned page" refers to a page that has had one of the get_user_pages()
 275 * variants called on that page.
 276 *
 277 * For each page in the @pages array, make that page (or its head page, if a
 278 * compound page) dirty, if @make_dirty is true, and if the page was previously
 279 * listed as clean. In any case, releases all pages using unpin_user_page(),
 280 * possibly via unpin_user_pages(), for the non-dirty case.
 281 *
 282 * Please see the unpin_user_page() documentation for details.
 283 *
 284 * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
 285 * required, then the caller should a) verify that this is really correct,
 286 * because _lock() is usually required, and b) hand code it:
 287 * set_page_dirty_lock(), unpin_user_page().
 288 *
 289 */
 290void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 291				 bool make_dirty)
 292{
 293	unsigned long i;
 294	struct folio *folio;
 295	unsigned int nr;
 296
 297	if (!make_dirty) {
 298		unpin_user_pages(pages, npages);
 299		return;
 300	}
 301
 302	sanity_check_pinned_pages(pages, npages);
 303	for (i = 0; i < npages; i += nr) {
 304		folio = gup_folio_next(pages, npages, i, &nr);
 305		/*
 306		 * Checking PageDirty at this point may race with
 307		 * clear_page_dirty_for_io(), but that's OK. Two key
 308		 * cases:
 309		 *
 310		 * 1) This code sees the page as already dirty, so it
 311		 * skips the call to set_page_dirty(). That could happen
 312		 * because clear_page_dirty_for_io() called
 313		 * folio_mkclean(), followed by set_page_dirty().
 314		 * However, now the page is going to get written back,
 315		 * which meets the original intention of setting it
 316		 * dirty, so all is well: clear_page_dirty_for_io() goes
 317		 * on to call TestClearPageDirty(), and write the page
 318		 * back.
 319		 *
 320		 * 2) This code sees the page as clean, so it calls
 321		 * set_page_dirty(). The page stays dirty, despite being
 322		 * written back, so it gets written back again in the
 323		 * next writeback cycle. This is harmless.
 324		 */
 325		if (!folio_test_dirty(folio)) {
 326			folio_lock(folio);
 327			folio_mark_dirty(folio);
 328			folio_unlock(folio);
 329		}
 330		gup_put_folio(folio, nr, FOLL_PIN);
 331	}
 332}
 333EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
 334
 335/**
 336 * unpin_user_page_range_dirty_lock() - release and optionally dirty
 337 * gup-pinned page range
 338 *
 339 * @page:  the starting page of a range maybe marked dirty, and definitely released.
 340 * @npages: number of consecutive pages to release.
 341 * @make_dirty: whether to mark the pages dirty
 342 *
 343 * "gup-pinned page range" refers to a range of pages that has had one of the
 344 * pin_user_pages() variants called on that page.
 345 *
 346 * For the page ranges defined by [page .. page+npages], make that range (or
 347 * its head pages, if a compound page) dirty, if @make_dirty is true, and if the
 348 * page range was previously listed as clean.
 349 *
 350 * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
 351 * required, then the caller should a) verify that this is really correct,
 352 * because _lock() is usually required, and b) hand code it:
 353 * set_page_dirty_lock(), unpin_user_page().
 354 *
 355 */
 356void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
 357				      bool make_dirty)
 358{
 359	unsigned long i;
 360	struct folio *folio;
 361	unsigned int nr;
 362
 363	for (i = 0; i < npages; i += nr) {
 364		folio = gup_folio_range_next(page, npages, i, &nr);
 365		if (make_dirty && !folio_test_dirty(folio)) {
 366			folio_lock(folio);
 367			folio_mark_dirty(folio);
 368			folio_unlock(folio);
 369		}
 370		gup_put_folio(folio, nr, FOLL_PIN);
 371	}
 372}
 373EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
 374
 375static void gup_fast_unpin_user_pages(struct page **pages, unsigned long npages)
 376{
 377	unsigned long i;
 378	struct folio *folio;
 379	unsigned int nr;
 380
 381	/*
 382	 * Don't perform any sanity checks because we might have raced with
 383	 * fork() and some anonymous pages might now actually be shared --
 384	 * which is why we're unpinning after all.
 385	 */
 386	for (i = 0; i < npages; i += nr) {
 387		folio = gup_folio_next(pages, npages, i, &nr);
 388		gup_put_folio(folio, nr, FOLL_PIN);
 389	}
 390}
 391
 392/**
 393 * unpin_user_pages() - release an array of gup-pinned pages.
 394 * @pages:  array of pages to be marked dirty and released.
 395 * @npages: number of pages in the @pages array.
 396 *
 397 * For each page in the @pages array, release the page using unpin_user_page().
 398 *
 399 * Please see the unpin_user_page() documentation for details.
 400 */
 401void unpin_user_pages(struct page **pages, unsigned long npages)
 402{
 403	unsigned long i;
 404	struct folio *folio;
 405	unsigned int nr;
 406
 407	/*
 408	 * If this WARN_ON() fires, then the system *might* be leaking pages (by
 409	 * leaving them pinned), but probably not. More likely, gup/pup returned
 410	 * a hard -ERRNO error to the caller, who erroneously passed it here.
 411	 */
 412	if (WARN_ON(IS_ERR_VALUE(npages)))
 413		return;
 414
 415	sanity_check_pinned_pages(pages, npages);
 416	for (i = 0; i < npages; i += nr) {
 417		if (!pages[i]) {
 418			nr = 1;
 419			continue;
 420		}
 421		folio = gup_folio_next(pages, npages, i, &nr);
 422		gup_put_folio(folio, nr, FOLL_PIN);
 423	}
 424}
 425EXPORT_SYMBOL(unpin_user_pages);
 426
 427/**
 428 * unpin_user_folio() - release pages of a folio
 429 * @folio:  pointer to folio to be released
 430 * @npages: number of pages of same folio
 431 *
 432 * Release npages of the folio
 433 */
 434void unpin_user_folio(struct folio *folio, unsigned long npages)
 435{
 436	gup_put_folio(folio, npages, FOLL_PIN);
 437}
 438EXPORT_SYMBOL(unpin_user_folio);
 439
 440/**
 441 * unpin_folios() - release an array of gup-pinned folios.
 442 * @folios:  array of folios to be marked dirty and released.
 443 * @nfolios: number of folios in the @folios array.
 444 *
 445 * For each folio in the @folios array, release the folio using gup_put_folio.
 446 *
 447 * Please see the unpin_folio() documentation for details.
 448 */
 449void unpin_folios(struct folio **folios, unsigned long nfolios)
 450{
 451	unsigned long i = 0, j;
 452
 453	/*
 454	 * If this WARN_ON() fires, then the system *might* be leaking folios
 455	 * (by leaving them pinned), but probably not. More likely, gup/pup
 456	 * returned a hard -ERRNO error to the caller, who erroneously passed
 457	 * it here.
 458	 */
 459	if (WARN_ON(IS_ERR_VALUE(nfolios)))
 460		return;
 461
 462	while (i < nfolios) {
 463		for (j = i + 1; j < nfolios; j++)
 464			if (folios[i] != folios[j])
 465				break;
 466
 467		if (folios[i])
 468			gup_put_folio(folios[i], j - i, FOLL_PIN);
 469		i = j;
 470	}
 471}
 472EXPORT_SYMBOL_GPL(unpin_folios);
 473
 474/*
 475 * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's
 476 * lifecycle.  Avoid setting the bit unless necessary, or it might cause write
 477 * cache bouncing on large SMP machines for concurrent pinned gups.
 478 */
 479static inline void mm_set_has_pinned_flag(unsigned long *mm_flags)
 480{
 481	if (!test_bit(MMF_HAS_PINNED, mm_flags))
 482		set_bit(MMF_HAS_PINNED, mm_flags);
 483}
 484
 485#ifdef CONFIG_MMU
 486
 487#ifdef CONFIG_HAVE_GUP_FAST
 488static int record_subpages(struct page *page, unsigned long sz,
 489			   unsigned long addr, unsigned long end,
 490			   struct page **pages)
 491{
 492	struct page *start_page;
 493	int nr;
 494
 495	start_page = nth_page(page, (addr & (sz - 1)) >> PAGE_SHIFT);
 496	for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
 497		pages[nr] = nth_page(start_page, nr);
 498
 499	return nr;
 500}
 501
 502/**
 503 * try_grab_folio_fast() - Attempt to get or pin a folio in fast path.
 504 * @page:  pointer to page to be grabbed
 505 * @refs:  the value to (effectively) add to the folio's refcount
 506 * @flags: gup flags: these are the FOLL_* flag values.
 507 *
 508 * "grab" names in this file mean, "look at flags to decide whether to use
 509 * FOLL_PIN or FOLL_GET behavior, when incrementing the folio's refcount.
 510 *
 511 * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the
 512 * same time. (That's true throughout the get_user_pages*() and
 513 * pin_user_pages*() APIs.) Cases:
 514 *
 515 *    FOLL_GET: folio's refcount will be incremented by @refs.
 516 *
 517 *    FOLL_PIN on large folios: folio's refcount will be incremented by
 518 *    @refs, and its pincount will be incremented by @refs.
 519 *
 520 *    FOLL_PIN on single-page folios: folio's refcount will be incremented by
 521 *    @refs * GUP_PIN_COUNTING_BIAS.
 522 *
 523 * Return: The folio containing @page (with refcount appropriately
 524 * incremented) for success, or NULL upon failure. If neither FOLL_GET
 525 * nor FOLL_PIN was set, that's considered failure, and furthermore,
 526 * a likely bug in the caller, so a warning is also emitted.
 527 *
 528 * It uses add ref unless zero to elevate the folio refcount and must be called
 529 * in fast path only.
 530 */
 531static struct folio *try_grab_folio_fast(struct page *page, int refs,
 532					 unsigned int flags)
 533{
 534	struct folio *folio;
 535
 536	/* Raise warn if it is not called in fast GUP */
 537	VM_WARN_ON_ONCE(!irqs_disabled());
 538
 539	if (WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == 0))
 540		return NULL;
 541
 542	if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)))
 543		return NULL;
 544
 545	if (flags & FOLL_GET)
 546		return try_get_folio(page, refs);
 547
 548	/* FOLL_PIN is set */
 549
 550	/*
 551	 * Don't take a pin on the zero page - it's not going anywhere
 552	 * and it is used in a *lot* of places.
 553	 */
 554	if (is_zero_page(page))
 555		return page_folio(page);
 556
 557	folio = try_get_folio(page, refs);
 558	if (!folio)
 559		return NULL;
 560
 561	/*
 562	 * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
 563	 * right zone, so fail and let the caller fall back to the slow
 564	 * path.
 565	 */
 566	if (unlikely((flags & FOLL_LONGTERM) &&
 567		     !folio_is_longterm_pinnable(folio))) {
 568		if (!put_devmap_managed_folio_refs(folio, refs))
 569			folio_put_refs(folio, refs);
 570		return NULL;
 571	}
 572
 573	/*
 574	 * When pinning a large folio, use an exact count to track it.
 575	 *
 576	 * However, be sure to *also* increment the normal folio
 577	 * refcount field at least once, so that the folio really
 578	 * is pinned.  That's why the refcount from the earlier
 579	 * try_get_folio() is left intact.
 580	 */
 581	if (folio_test_large(folio))
 582		atomic_add(refs, &folio->_pincount);
 583	else
 584		folio_ref_add(folio,
 585				refs * (GUP_PIN_COUNTING_BIAS - 1));
 586	/*
 587	 * Adjust the pincount before re-checking the PTE for changes.
 588	 * This is essentially a smp_mb() and is paired with a memory
 589	 * barrier in folio_try_share_anon_rmap_*().
 590	 */
 591	smp_mb__after_atomic();
 592
 593	node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
 594
 595	return folio;
 596}
 597#endif	/* CONFIG_HAVE_GUP_FAST */
 598
 599static struct page *no_page_table(struct vm_area_struct *vma,
 600				  unsigned int flags, unsigned long address)
 601{
 602	if (!(flags & FOLL_DUMP))
 603		return NULL;
 604
 605	/*
 606	 * When core dumping, we don't want to allocate unnecessary pages or
 607	 * page tables.  Return error instead of NULL to skip handle_mm_fault,
 608	 * then get_dump_page() will return NULL to leave a hole in the dump.
 609	 * But we can only make this optimization where a hole would surely
 610	 * be zero-filled if handle_mm_fault() actually did handle it.
 611	 */
 612	if (is_vm_hugetlb_page(vma)) {
 613		struct hstate *h = hstate_vma(vma);
 614
 615		if (!hugetlbfs_pagecache_present(h, vma, address))
 616			return ERR_PTR(-EFAULT);
 617	} else if ((vma_is_anonymous(vma) || !vma->vm_ops->fault)) {
 618		return ERR_PTR(-EFAULT);
 619	}
 620
 621	return NULL;
 622}
 623
 624#ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
 625static struct page *follow_huge_pud(struct vm_area_struct *vma,
 626				    unsigned long addr, pud_t *pudp,
 627				    int flags, struct follow_page_context *ctx)
 628{
 629	struct mm_struct *mm = vma->vm_mm;
 630	struct page *page;
 631	pud_t pud = *pudp;
 632	unsigned long pfn = pud_pfn(pud);
 633	int ret;
 634
 635	assert_spin_locked(pud_lockptr(mm, pudp));
 636
 637	if ((flags & FOLL_WRITE) && !pud_write(pud))
 638		return NULL;
 639
 640	if (!pud_present(pud))
 641		return NULL;
 642
 643	pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
 644
 645	if (IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
 646	    pud_devmap(pud)) {
 647		/*
 648		 * device mapped pages can only be returned if the caller
 649		 * will manage the page reference count.
 650		 *
 651		 * At least one of FOLL_GET | FOLL_PIN must be set, so
 652		 * assert that here:
 653		 */
 654		if (!(flags & (FOLL_GET | FOLL_PIN)))
 655			return ERR_PTR(-EEXIST);
 656
 657		if (flags & FOLL_TOUCH)
 658			touch_pud(vma, addr, pudp, flags & FOLL_WRITE);
 659
 660		ctx->pgmap = get_dev_pagemap(pfn, ctx->pgmap);
 661		if (!ctx->pgmap)
 662			return ERR_PTR(-EFAULT);
 663	}
 664
 665	page = pfn_to_page(pfn);
 666
 667	if (!pud_devmap(pud) && !pud_write(pud) &&
 668	    gup_must_unshare(vma, flags, page))
 669		return ERR_PTR(-EMLINK);
 670
 671	ret = try_grab_folio(page_folio(page), 1, flags);
 672	if (ret)
 673		page = ERR_PTR(ret);
 674	else
 675		ctx->page_mask = HPAGE_PUD_NR - 1;
 676
 677	return page;
 678}
 679
 680/* FOLL_FORCE can write to even unwritable PMDs in COW mappings. */
 681static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
 682					struct vm_area_struct *vma,
 683					unsigned int flags)
 684{
 685	/* If the pmd is writable, we can write to the page. */
 686	if (pmd_write(pmd))
 687		return true;
 688
 689	/* Maybe FOLL_FORCE is set to override it? */
 690	if (!(flags & FOLL_FORCE))
 691		return false;
 692
 693	/* But FOLL_FORCE has no effect on shared mappings */
 694	if (vma->vm_flags & (VM_MAYSHARE | VM_SHARED))
 695		return false;
 696
 697	/* ... or read-only private ones */
 698	if (!(vma->vm_flags & VM_MAYWRITE))
 699		return false;
 700
 701	/* ... or already writable ones that just need to take a write fault */
 702	if (vma->vm_flags & VM_WRITE)
 703		return false;
 704
 705	/*
 706	 * See can_change_pte_writable(): we broke COW and could map the page
 707	 * writable if we have an exclusive anonymous page ...
 708	 */
 709	if (!page || !PageAnon(page) || !PageAnonExclusive(page))
 710		return false;
 711
 712	/* ... and a write-fault isn't required for other reasons. */
 713	if (pmd_needs_soft_dirty_wp(vma, pmd))
 714		return false;
 715	return !userfaultfd_huge_pmd_wp(vma, pmd);
 716}
 717
 718static struct page *follow_huge_pmd(struct vm_area_struct *vma,
 719				    unsigned long addr, pmd_t *pmd,
 720				    unsigned int flags,
 721				    struct follow_page_context *ctx)
 722{
 723	struct mm_struct *mm = vma->vm_mm;
 724	pmd_t pmdval = *pmd;
 725	struct page *page;
 726	int ret;
 727
 728	assert_spin_locked(pmd_lockptr(mm, pmd));
 729
 730	page = pmd_page(pmdval);
 731	if ((flags & FOLL_WRITE) &&
 732	    !can_follow_write_pmd(pmdval, page, vma, flags))
 733		return NULL;
 734
 735	/* Avoid dumping huge zero page */
 736	if ((flags & FOLL_DUMP) && is_huge_zero_pmd(pmdval))
 737		return ERR_PTR(-EFAULT);
 738
 739	if (pmd_protnone(*pmd) && !gup_can_follow_protnone(vma, flags))
 740		return NULL;
 741
 742	if (!pmd_write(pmdval) && gup_must_unshare(vma, flags, page))
 743		return ERR_PTR(-EMLINK);
 744
 745	VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
 746			!PageAnonExclusive(page), page);
 747
 748	ret = try_grab_folio(page_folio(page), 1, flags);
 749	if (ret)
 750		return ERR_PTR(ret);
 751
 752#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 753	if (pmd_trans_huge(pmdval) && (flags & FOLL_TOUCH))
 754		touch_pmd(vma, addr, pmd, flags & FOLL_WRITE);
 755#endif	/* CONFIG_TRANSPARENT_HUGEPAGE */
 756
 757	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
 758	ctx->page_mask = HPAGE_PMD_NR - 1;
 759
 760	return page;
 761}
 762
 763#else  /* CONFIG_PGTABLE_HAS_HUGE_LEAVES */
 764static struct page *follow_huge_pud(struct vm_area_struct *vma,
 765				    unsigned long addr, pud_t *pudp,
 766				    int flags, struct follow_page_context *ctx)
 767{
 768	return NULL;
 769}
 770
 771static struct page *follow_huge_pmd(struct vm_area_struct *vma,
 772				    unsigned long addr, pmd_t *pmd,
 773				    unsigned int flags,
 774				    struct follow_page_context *ctx)
 775{
 776	return NULL;
 777}
 778#endif	/* CONFIG_PGTABLE_HAS_HUGE_LEAVES */
 779
 780static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
 781		pte_t *pte, unsigned int flags)
 782{
 783	if (flags & FOLL_TOUCH) {
 784		pte_t orig_entry = ptep_get(pte);
 785		pte_t entry = orig_entry;
 786
 787		if (flags & FOLL_WRITE)
 788			entry = pte_mkdirty(entry);
 789		entry = pte_mkyoung(entry);
 790
 791		if (!pte_same(orig_entry, entry)) {
 792			set_pte_at(vma->vm_mm, address, pte, entry);
 793			update_mmu_cache(vma, address, pte);
 794		}
 795	}
 796
 797	/* Proper page table entry exists, but no corresponding struct page */
 798	return -EEXIST;
 799}
 800
 801/* FOLL_FORCE can write to even unwritable PTEs in COW mappings. */
 802static inline bool can_follow_write_pte(pte_t pte, struct page *page,
 803					struct vm_area_struct *vma,
 804					unsigned int flags)
 805{
 806	/* If the pte is writable, we can write to the page. */
 807	if (pte_write(pte))
 808		return true;
 809
 810	/* Maybe FOLL_FORCE is set to override it? */
 811	if (!(flags & FOLL_FORCE))
 812		return false;
 813
 814	/* But FOLL_FORCE has no effect on shared mappings */
 815	if (vma->vm_flags & (VM_MAYSHARE | VM_SHARED))
 816		return false;
 817
 818	/* ... or read-only private ones */
 819	if (!(vma->vm_flags & VM_MAYWRITE))
 820		return false;
 821
 822	/* ... or already writable ones that just need to take a write fault */
 823	if (vma->vm_flags & VM_WRITE)
 824		return false;
 825
 826	/*
 827	 * See can_change_pte_writable(): we broke COW and could map the page
 828	 * writable if we have an exclusive anonymous page ...
 829	 */
 830	if (!page || !PageAnon(page) || !PageAnonExclusive(page))
 831		return false;
 832
 833	/* ... and a write-fault isn't required for other reasons. */
 834	if (pte_needs_soft_dirty_wp(vma, pte))
 835		return false;
 836	return !userfaultfd_pte_wp(vma, pte);
 837}
 838
 839static struct page *follow_page_pte(struct vm_area_struct *vma,
 840		unsigned long address, pmd_t *pmd, unsigned int flags,
 841		struct dev_pagemap **pgmap)
 842{
 843	struct mm_struct *mm = vma->vm_mm;
 844	struct folio *folio;
 845	struct page *page;
 846	spinlock_t *ptl;
 847	pte_t *ptep, pte;
 848	int ret;
 849
 850	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
 851	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
 852			 (FOLL_PIN | FOLL_GET)))
 853		return ERR_PTR(-EINVAL);
 854
 855	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 856	if (!ptep)
 857		return no_page_table(vma, flags, address);
 858	pte = ptep_get(ptep);
 859	if (!pte_present(pte))
 860		goto no_page;
 861	if (pte_protnone(pte) && !gup_can_follow_protnone(vma, flags))
 862		goto no_page;
 863
 864	page = vm_normal_page(vma, address, pte);
 865
 866	/*
 867	 * We only care about anon pages in can_follow_write_pte() and don't
 868	 * have to worry about pte_devmap() because they are never anon.
 869	 */
 870	if ((flags & FOLL_WRITE) &&
 871	    !can_follow_write_pte(pte, page, vma, flags)) {
 872		page = NULL;
 873		goto out;
 874	}
 875
 876	if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
 877		/*
 878		 * Only return device mapping pages in the FOLL_GET or FOLL_PIN
 879		 * case since they are only valid while holding the pgmap
 880		 * reference.
 881		 */
 882		*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
 883		if (*pgmap)
 884			page = pte_page(pte);
 885		else
 886			goto no_page;
 887	} else if (unlikely(!page)) {
 888		if (flags & FOLL_DUMP) {
 889			/* Avoid special (like zero) pages in core dumps */
 890			page = ERR_PTR(-EFAULT);
 891			goto out;
 892		}
 893
 894		if (is_zero_pfn(pte_pfn(pte))) {
 895			page = pte_page(pte);
 896		} else {
 897			ret = follow_pfn_pte(vma, address, ptep, flags);
 898			page = ERR_PTR(ret);
 899			goto out;
 900		}
 901	}
 902	folio = page_folio(page);
 903
 904	if (!pte_write(pte) && gup_must_unshare(vma, flags, page)) {
 905		page = ERR_PTR(-EMLINK);
 906		goto out;
 907	}
 908
 909	VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
 910		       !PageAnonExclusive(page), page);
 911
 912	/* try_grab_folio() does nothing unless FOLL_GET or FOLL_PIN is set. */
 913	ret = try_grab_folio(folio, 1, flags);
 914	if (unlikely(ret)) {
 915		page = ERR_PTR(ret);
 916		goto out;
 917	}
 918
 919	/*
 920	 * We need to make the page accessible if and only if we are going
 921	 * to access its content (the FOLL_PIN case).  Please see
 922	 * Documentation/core-api/pin_user_pages.rst for details.
 923	 */
 924	if (flags & FOLL_PIN) {
 925		ret = arch_make_folio_accessible(folio);
 926		if (ret) {
 927			unpin_user_page(page);
 928			page = ERR_PTR(ret);
 929			goto out;
 930		}
 931	}
 932	if (flags & FOLL_TOUCH) {
 933		if ((flags & FOLL_WRITE) &&
 934		    !pte_dirty(pte) && !folio_test_dirty(folio))
 935			folio_mark_dirty(folio);
 936		/*
 937		 * pte_mkyoung() would be more correct here, but atomic care
 938		 * is needed to avoid losing the dirty bit: it is easier to use
 939		 * folio_mark_accessed().
 940		 */
 941		folio_mark_accessed(folio);
 942	}
 943out:
 944	pte_unmap_unlock(ptep, ptl);
 945	return page;
 946no_page:
 947	pte_unmap_unlock(ptep, ptl);
 948	if (!pte_none(pte))
 949		return NULL;
 950	return no_page_table(vma, flags, address);
 951}
 952
 953static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 954				    unsigned long address, pud_t *pudp,
 955				    unsigned int flags,
 956				    struct follow_page_context *ctx)
 957{
 958	pmd_t *pmd, pmdval;
 959	spinlock_t *ptl;
 960	struct page *page;
 961	struct mm_struct *mm = vma->vm_mm;
 962
 963	pmd = pmd_offset(pudp, address);
 964	pmdval = pmdp_get_lockless(pmd);
 965	if (pmd_none(pmdval))
 966		return no_page_table(vma, flags, address);
 967	if (!pmd_present(pmdval))
 968		return no_page_table(vma, flags, address);
 969	if (pmd_devmap(pmdval)) {
 970		ptl = pmd_lock(mm, pmd);
 971		page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
 972		spin_unlock(ptl);
 973		if (page)
 974			return page;
 975		return no_page_table(vma, flags, address);
 976	}
 977	if (likely(!pmd_leaf(pmdval)))
 978		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 979
 980	if (pmd_protnone(pmdval) && !gup_can_follow_protnone(vma, flags))
 981		return no_page_table(vma, flags, address);
 982
 983	ptl = pmd_lock(mm, pmd);
 984	pmdval = *pmd;
 985	if (unlikely(!pmd_present(pmdval))) {
 986		spin_unlock(ptl);
 987		return no_page_table(vma, flags, address);
 988	}
 989	if (unlikely(!pmd_leaf(pmdval))) {
 990		spin_unlock(ptl);
 991		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 992	}
 993	if (pmd_trans_huge(pmdval) && (flags & FOLL_SPLIT_PMD)) {
 994		spin_unlock(ptl);
 995		split_huge_pmd(vma, pmd, address);
 996		/* If pmd was left empty, stuff a page table in there quickly */
 997		return pte_alloc(mm, pmd) ? ERR_PTR(-ENOMEM) :
 998			follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 999	}
1000	page = follow_huge_pmd(vma, address, pmd, flags, ctx);
1001	spin_unlock(ptl);
1002	return page;
1003}
1004
1005static struct page *follow_pud_mask(struct vm_area_struct *vma,
1006				    unsigned long address, p4d_t *p4dp,
1007				    unsigned int flags,
1008				    struct follow_page_context *ctx)
1009{
1010	pud_t *pudp, pud;
1011	spinlock_t *ptl;
1012	struct page *page;
1013	struct mm_struct *mm = vma->vm_mm;
1014
1015	pudp = pud_offset(p4dp, address);
1016	pud = READ_ONCE(*pudp);
1017	if (!pud_present(pud))
1018		return no_page_table(vma, flags, address);
1019	if (pud_leaf(pud)) {
1020		ptl = pud_lock(mm, pudp);
1021		page = follow_huge_pud(vma, address, pudp, flags, ctx);
1022		spin_unlock(ptl);
1023		if (page)
1024			return page;
1025		return no_page_table(vma, flags, address);
1026	}
1027	if (unlikely(pud_bad(pud)))
1028		return no_page_table(vma, flags, address);
1029
1030	return follow_pmd_mask(vma, address, pudp, flags, ctx);
1031}
1032
1033static struct page *follow_p4d_mask(struct vm_area_struct *vma,
1034				    unsigned long address, pgd_t *pgdp,
1035				    unsigned int flags,
1036				    struct follow_page_context *ctx)
1037{
1038	p4d_t *p4dp, p4d;
1039
1040	p4dp = p4d_offset(pgdp, address);
1041	p4d = READ_ONCE(*p4dp);
1042	BUILD_BUG_ON(p4d_leaf(p4d));
1043
1044	if (!p4d_present(p4d) || p4d_bad(p4d))
1045		return no_page_table(vma, flags, address);
1046
1047	return follow_pud_mask(vma, address, p4dp, flags, ctx);
1048}
1049
1050/**
1051 * follow_page_mask - look up a page descriptor from a user-virtual address
1052 * @vma: vm_area_struct mapping @address
1053 * @address: virtual address to look up
1054 * @flags: flags modifying lookup behaviour
1055 * @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
1056 *       pointer to output page_mask
1057 *
1058 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
1059 *
1060 * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
1061 * the device's dev_pagemap metadata to avoid repeating expensive lookups.
1062 *
1063 * When getting an anonymous page and the caller has to trigger unsharing
1064 * of a shared anonymous page first, -EMLINK is returned. The caller should
1065 * trigger a fault with FAULT_FLAG_UNSHARE set. Note that unsharing is only
1066 * relevant with FOLL_PIN and !FOLL_WRITE.
1067 *
1068 * On output, the @ctx->page_mask is set according to the size of the page.
1069 *
1070 * Return: the mapped (struct page *), %NULL if no mapping exists, or
1071 * an error pointer if there is a mapping to something not represented
1072 * by a page descriptor (see also vm_normal_page()).
1073 */
1074static struct page *follow_page_mask(struct vm_area_struct *vma,
1075			      unsigned long address, unsigned int flags,
1076			      struct follow_page_context *ctx)
1077{
1078	pgd_t *pgd;
1079	struct mm_struct *mm = vma->vm_mm;
1080	struct page *page;
1081
1082	vma_pgtable_walk_begin(vma);
1083
1084	ctx->page_mask = 0;
1085	pgd = pgd_offset(mm, address);
1086
1087	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
1088		page = no_page_table(vma, flags, address);
1089	else
1090		page = follow_p4d_mask(vma, address, pgd, flags, ctx);
1091
1092	vma_pgtable_walk_end(vma);
1093
1094	return page;
1095}
1096
1097static int get_gate_page(struct mm_struct *mm, unsigned long address,
1098		unsigned int gup_flags, struct vm_area_struct **vma,
1099		struct page **page)
1100{
1101	pgd_t *pgd;
1102	p4d_t *p4d;
1103	pud_t *pud;
1104	pmd_t *pmd;
1105	pte_t *pte;
1106	pte_t entry;
1107	int ret = -EFAULT;
1108
1109	/* user gate pages are read-only */
1110	if (gup_flags & FOLL_WRITE)
1111		return -EFAULT;
1112	if (address > TASK_SIZE)
1113		pgd = pgd_offset_k(address);
1114	else
1115		pgd = pgd_offset_gate(mm, address);
1116	if (pgd_none(*pgd))
1117		return -EFAULT;
1118	p4d = p4d_offset(pgd, address);
1119	if (p4d_none(*p4d))
1120		return -EFAULT;
1121	pud = pud_offset(p4d, address);
1122	if (pud_none(*pud))
1123		return -EFAULT;
1124	pmd = pmd_offset(pud, address);
1125	if (!pmd_present(*pmd))
1126		return -EFAULT;
1127	pte = pte_offset_map(pmd, address);
1128	if (!pte)
1129		return -EFAULT;
1130	entry = ptep_get(pte);
1131	if (pte_none(entry))
1132		goto unmap;
1133	*vma = get_gate_vma(mm);
1134	if (!page)
1135		goto out;
1136	*page = vm_normal_page(*vma, address, entry);
1137	if (!*page) {
1138		if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(entry)))
1139			goto unmap;
1140		*page = pte_page(entry);
1141	}
1142	ret = try_grab_folio(page_folio(*page), 1, gup_flags);
1143	if (unlikely(ret))
1144		goto unmap;
1145out:
1146	ret = 0;
1147unmap:
1148	pte_unmap(pte);
1149	return ret;
1150}
1151
1152/*
1153 * mmap_lock must be held on entry.  If @flags has FOLL_UNLOCKABLE but not
1154 * FOLL_NOWAIT, the mmap_lock may be released.  If it is, *@locked will be set
1155 * to 0 and -EBUSY returned.
1156 */
1157static int faultin_page(struct vm_area_struct *vma,
1158		unsigned long address, unsigned int flags, bool unshare,
1159		int *locked)
1160{
1161	unsigned int fault_flags = 0;
1162	vm_fault_t ret;
1163
1164	if (flags & FOLL_NOFAULT)
1165		return -EFAULT;
1166	if (flags & FOLL_WRITE)
1167		fault_flags |= FAULT_FLAG_WRITE;
1168	if (flags & FOLL_REMOTE)
1169		fault_flags |= FAULT_FLAG_REMOTE;
1170	if (flags & FOLL_UNLOCKABLE) {
1171		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1172		/*
1173		 * FAULT_FLAG_INTERRUPTIBLE is opt-in. GUP callers must set
1174		 * FOLL_INTERRUPTIBLE to enable FAULT_FLAG_INTERRUPTIBLE.
1175		 * That's because some callers may not be prepared to
1176		 * handle early exits caused by non-fatal signals.
1177		 */
1178		if (flags & FOLL_INTERRUPTIBLE)
1179			fault_flags |= FAULT_FLAG_INTERRUPTIBLE;
1180	}
1181	if (flags & FOLL_NOWAIT)
1182		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
1183	if (flags & FOLL_TRIED) {
1184		/*
1185		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
1186		 * can co-exist
1187		 */
1188		fault_flags |= FAULT_FLAG_TRIED;
1189	}
1190	if (unshare) {
1191		fault_flags |= FAULT_FLAG_UNSHARE;
1192		/* FAULT_FLAG_WRITE and FAULT_FLAG_UNSHARE are incompatible */
1193		VM_BUG_ON(fault_flags & FAULT_FLAG_WRITE);
1194	}
1195
1196	ret = handle_mm_fault(vma, address, fault_flags, NULL);
1197
1198	if (ret & VM_FAULT_COMPLETED) {
1199		/*
1200		 * With FAULT_FLAG_RETRY_NOWAIT we'll never release the
1201		 * mmap lock in the page fault handler. Sanity check this.
1202		 */
1203		WARN_ON_ONCE(fault_flags & FAULT_FLAG_RETRY_NOWAIT);
1204		*locked = 0;
1205
1206		/*
1207		 * We should do the same as VM_FAULT_RETRY, but let's not
1208		 * return -EBUSY since that's not reflecting the reality of
1209		 * what has happened - we've just fully completed a page
1210		 * fault, with the mmap lock released.  Use -EAGAIN to show
1211		 * that we want to take the mmap lock _again_.
1212		 */
1213		return -EAGAIN;
1214	}
1215
1216	if (ret & VM_FAULT_ERROR) {
1217		int err = vm_fault_to_errno(ret, flags);
1218
1219		if (err)
1220			return err;
1221		BUG();
1222	}
1223
1224	if (ret & VM_FAULT_RETRY) {
1225		if (!(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
1226			*locked = 0;
1227		return -EBUSY;
1228	}
1229
1230	return 0;
1231}
1232
1233/*
1234 * Writing to file-backed mappings which require folio dirty tracking using GUP
1235 * is a fundamentally broken operation, as kernel write access to GUP mappings
1236 * do not adhere to the semantics expected by a file system.
1237 *
1238 * Consider the following scenario:-
1239 *
1240 * 1. A folio is written to via GUP which write-faults the memory, notifying
1241 *    the file system and dirtying the folio.
1242 * 2. Later, writeback is triggered, resulting in the folio being cleaned and
1243 *    the PTE being marked read-only.
1244 * 3. The GUP caller writes to the folio, as it is mapped read/write via the
1245 *    direct mapping.
1246 * 4. The GUP caller, now done with the page, unpins it and sets it dirty
1247 *    (though it does not have to).
1248 *
1249 * This results in both data being written to a folio without writenotify, and
1250 * the folio being dirtied unexpectedly (if the caller decides to do so).
1251 */
1252static bool writable_file_mapping_allowed(struct vm_area_struct *vma,
1253					  unsigned long gup_flags)
1254{
1255	/*
1256	 * If we aren't pinning then no problematic write can occur. A long term
1257	 * pin is the most egregious case so this is the case we disallow.
1258	 */
1259	if ((gup_flags & (FOLL_PIN | FOLL_LONGTERM)) !=
1260	    (FOLL_PIN | FOLL_LONGTERM))
1261		return true;
1262
1263	/*
1264	 * If the VMA does not require dirty tracking then no problematic write
1265	 * can occur either.
1266	 */
1267	return !vma_needs_dirty_tracking(vma);
1268}
1269
1270static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
1271{
1272	vm_flags_t vm_flags = vma->vm_flags;
1273	int write = (gup_flags & FOLL_WRITE);
1274	int foreign = (gup_flags & FOLL_REMOTE);
1275	bool vma_anon = vma_is_anonymous(vma);
1276
1277	if (vm_flags & (VM_IO | VM_PFNMAP))
1278		return -EFAULT;
1279
1280	if ((gup_flags & FOLL_ANON) && !vma_anon)
1281		return -EFAULT;
1282
1283	if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
1284		return -EOPNOTSUPP;
1285
1286	if (vma_is_secretmem(vma))
1287		return -EFAULT;
1288
1289	if (write) {
1290		if (!vma_anon &&
1291		    !writable_file_mapping_allowed(vma, gup_flags))
1292			return -EFAULT;
1293
1294		if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) {
1295			if (!(gup_flags & FOLL_FORCE))
1296				return -EFAULT;
1297			/* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
1298			if (is_vm_hugetlb_page(vma))
1299				return -EFAULT;
1300			/*
1301			 * We used to let the write,force case do COW in a
1302			 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
1303			 * set a breakpoint in a read-only mapping of an
1304			 * executable, without corrupting the file (yet only
1305			 * when that file had been opened for writing!).
1306			 * Anon pages in shared mappings are surprising: now
1307			 * just reject it.
1308			 */
1309			if (!is_cow_mapping(vm_flags))
1310				return -EFAULT;
1311		}
1312	} else if (!(vm_flags & VM_READ)) {
1313		if (!(gup_flags & FOLL_FORCE))
1314			return -EFAULT;
1315		/*
1316		 * Is there actually any vma we can reach here which does not
1317		 * have VM_MAYREAD set?
1318		 */
1319		if (!(vm_flags & VM_MAYREAD))
1320			return -EFAULT;
1321	}
1322	/*
1323	 * gups are always data accesses, not instruction
1324	 * fetches, so execute=false here
1325	 */
1326	if (!arch_vma_access_permitted(vma, write, false, foreign))
1327		return -EFAULT;
1328	return 0;
1329}
1330
1331/*
1332 * This is "vma_lookup()", but with a warning if we would have
1333 * historically expanded the stack in the GUP code.
1334 */
1335static struct vm_area_struct *gup_vma_lookup(struct mm_struct *mm,
1336	 unsigned long addr)
1337{
1338#ifdef CONFIG_STACK_GROWSUP
1339	return vma_lookup(mm, addr);
1340#else
1341	static volatile unsigned long next_warn;
1342	struct vm_area_struct *vma;
1343	unsigned long now, next;
1344
1345	vma = find_vma(mm, addr);
1346	if (!vma || (addr >= vma->vm_start))
1347		return vma;
1348
1349	/* Only warn for half-way relevant accesses */
1350	if (!(vma->vm_flags & VM_GROWSDOWN))
1351		return NULL;
1352	if (vma->vm_start - addr > 65536)
1353		return NULL;
1354
1355	/* Let's not warn more than once an hour.. */
1356	now = jiffies; next = next_warn;
1357	if (next && time_before(now, next))
1358		return NULL;
1359	next_warn = now + 60*60*HZ;
1360
1361	/* Let people know things may have changed. */
1362	pr_warn("GUP no longer grows the stack in %s (%d): %lx-%lx (%lx)\n",
1363		current->comm, task_pid_nr(current),
1364		vma->vm_start, vma->vm_end, addr);
1365	dump_stack();
1366	return NULL;
1367#endif
1368}
1369
1370/**
1371 * __get_user_pages() - pin user pages in memory
1372 * @mm:		mm_struct of target mm
1373 * @start:	starting user address
1374 * @nr_pages:	number of pages from start to pin
1375 * @gup_flags:	flags modifying pin behaviour
1376 * @pages:	array that receives pointers to the pages pinned.
1377 *		Should be at least nr_pages long. Or NULL, if caller
1378 *		only intends to ensure the pages are faulted in.
1379 * @locked:     whether we're still with the mmap_lock held
1380 *
1381 * Returns either number of pages pinned (which may be less than the
1382 * number requested), or an error. Details about the return value:
1383 *
1384 * -- If nr_pages is 0, returns 0.
1385 * -- If nr_pages is >0, but no pages were pinned, returns -errno.
1386 * -- If nr_pages is >0, and some pages were pinned, returns the number of
1387 *    pages pinned. Again, this may be less than nr_pages.
1388 * -- 0 return value is possible when the fault would need to be retried.
1389 *
1390 * The caller is responsible for releasing returned @pages, via put_page().
1391 *
1392 * Must be called with mmap_lock held.  It may be released.  See below.
1393 *
1394 * __get_user_pages walks a process's page tables and takes a reference to
1395 * each struct page that each user address corresponds to at a given
1396 * instant. That is, it takes the page that would be accessed if a user
1397 * thread accesses the given user virtual address at that instant.
1398 *
1399 * This does not guarantee that the page exists in the user mappings when
1400 * __get_user_pages returns, and there may even be a completely different
1401 * page there in some cases (eg. if mmapped pagecache has been invalidated
1402 * and subsequently re-faulted). However it does guarantee that the page
1403 * won't be freed completely. And mostly callers simply care that the page
1404 * contains data that was valid *at some point in time*. Typically, an IO
1405 * or similar operation cannot guarantee anything stronger anyway because
1406 * locks can't be held over the syscall boundary.
1407 *
1408 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
1409 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
1410 * appropriate) must be called after the page is finished with, and
1411 * before put_page is called.
1412 *
1413 * If FOLL_UNLOCKABLE is set without FOLL_NOWAIT then the mmap_lock may
1414 * be released. If this happens *@locked will be set to 0 on return.
1415 *
1416 * A caller using such a combination of @gup_flags must therefore hold the
1417 * mmap_lock for reading only, and recognize when it's been released. Otherwise,
1418 * it must be held for either reading or writing and will not be released.
1419 *
1420 * In most cases, get_user_pages or get_user_pages_fast should be used
1421 * instead of __get_user_pages. __get_user_pages should be used only if
1422 * you need some special @gup_flags.
1423 */
1424static long __get_user_pages(struct mm_struct *mm,
1425		unsigned long start, unsigned long nr_pages,
1426		unsigned int gup_flags, struct page **pages,
1427		int *locked)
1428{
1429	long ret = 0, i = 0;
1430	struct vm_area_struct *vma = NULL;
1431	struct follow_page_context ctx = { NULL };
1432
1433	if (!nr_pages)
1434		return 0;
1435
1436	start = untagged_addr_remote(mm, start);
1437
1438	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
1439
1440	do {
1441		struct page *page;
1442		unsigned int page_increm;
1443
1444		/* first iteration or cross vma bound */
1445		if (!vma || start >= vma->vm_end) {
1446			/*
1447			 * MADV_POPULATE_(READ|WRITE) wants to handle VMA
1448			 * lookups+error reporting differently.
1449			 */
1450			if (gup_flags & FOLL_MADV_POPULATE) {
1451				vma = vma_lookup(mm, start);
1452				if (!vma) {
1453					ret = -ENOMEM;
1454					goto out;
1455				}
1456				if (check_vma_flags(vma, gup_flags)) {
1457					ret = -EINVAL;
1458					goto out;
1459				}
1460				goto retry;
1461			}
1462			vma = gup_vma_lookup(mm, start);
1463			if (!vma && in_gate_area(mm, start)) {
1464				ret = get_gate_page(mm, start & PAGE_MASK,
1465						gup_flags, &vma,
1466						pages ? &page : NULL);
1467				if (ret)
1468					goto out;
1469				ctx.page_mask = 0;
1470				goto next_page;
1471			}
1472
1473			if (!vma) {
1474				ret = -EFAULT;
1475				goto out;
1476			}
1477			ret = check_vma_flags(vma, gup_flags);
1478			if (ret)
1479				goto out;
1480		}
1481retry:
1482		/*
1483		 * If we have a pending SIGKILL, don't keep faulting pages and
1484		 * potentially allocating memory.
1485		 */
1486		if (fatal_signal_pending(current)) {
1487			ret = -EINTR;
1488			goto out;
1489		}
1490		cond_resched();
1491
1492		page = follow_page_mask(vma, start, gup_flags, &ctx);
1493		if (!page || PTR_ERR(page) == -EMLINK) {
1494			ret = faultin_page(vma, start, gup_flags,
1495					   PTR_ERR(page) == -EMLINK, locked);
1496			switch (ret) {
1497			case 0:
1498				goto retry;
1499			case -EBUSY:
1500			case -EAGAIN:
1501				ret = 0;
1502				fallthrough;
1503			case -EFAULT:
1504			case -ENOMEM:
1505			case -EHWPOISON:
1506				goto out;
1507			}
1508			BUG();
1509		} else if (PTR_ERR(page) == -EEXIST) {
1510			/*
1511			 * Proper page table entry exists, but no corresponding
1512			 * struct page. If the caller expects **pages to be
1513			 * filled in, bail out now, because that can't be done
1514			 * for this page.
1515			 */
1516			if (pages) {
1517				ret = PTR_ERR(page);
1518				goto out;
1519			}
1520		} else if (IS_ERR(page)) {
1521			ret = PTR_ERR(page);
1522			goto out;
1523		}
1524next_page:
1525		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
1526		if (page_increm > nr_pages)
1527			page_increm = nr_pages;
1528
1529		if (pages) {
1530			struct page *subpage;
1531			unsigned int j;
1532
1533			/*
1534			 * This must be a large folio (and doesn't need to
1535			 * be the whole folio; it can be part of it), do
1536			 * the refcount work for all the subpages too.
1537			 *
1538			 * NOTE: here the page may not be the head page
1539			 * e.g. when start addr is not thp-size aligned.
1540			 * try_grab_folio() should have taken care of tail
1541			 * pages.
1542			 */
1543			if (page_increm > 1) {
1544				struct folio *folio = page_folio(page);
1545
1546				/*
1547				 * Since we already hold refcount on the
1548				 * large folio, this should never fail.
1549				 */
1550				if (try_grab_folio(folio, page_increm - 1,
1551						   gup_flags)) {
1552					/*
1553					 * Release the 1st page ref if the
1554					 * folio is problematic, fail hard.
1555					 */
1556					gup_put_folio(folio, 1, gup_flags);
1557					ret = -EFAULT;
1558					goto out;
1559				}
1560			}
1561
1562			for (j = 0; j < page_increm; j++) {
1563				subpage = nth_page(page, j);
1564				pages[i + j] = subpage;
1565				flush_anon_page(vma, subpage, start + j * PAGE_SIZE);
1566				flush_dcache_page(subpage);
1567			}
1568		}
1569
1570		i += page_increm;
1571		start += page_increm * PAGE_SIZE;
1572		nr_pages -= page_increm;
1573	} while (nr_pages);
1574out:
1575	if (ctx.pgmap)
1576		put_dev_pagemap(ctx.pgmap);
1577	return i ? i : ret;
1578}
1579
1580static bool vma_permits_fault(struct vm_area_struct *vma,
1581			      unsigned int fault_flags)
1582{
1583	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
1584	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
1585	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
1586
1587	if (!(vm_flags & vma->vm_flags))
1588		return false;
1589
1590	/*
1591	 * The architecture might have a hardware protection
1592	 * mechanism other than read/write that can deny access.
1593	 *
1594	 * gup always represents data access, not instruction
1595	 * fetches, so execute=false here:
1596	 */
1597	if (!arch_vma_access_permitted(vma, write, false, foreign))
1598		return false;
1599
1600	return true;
1601}
1602
1603/**
1604 * fixup_user_fault() - manually resolve a user page fault
1605 * @mm:		mm_struct of target mm
1606 * @address:	user address
1607 * @fault_flags:flags to pass down to handle_mm_fault()
1608 * @unlocked:	did we unlock the mmap_lock while retrying, maybe NULL if caller
1609 *		does not allow retry. If NULL, the caller must guarantee
1610 *		that fault_flags does not contain FAULT_FLAG_ALLOW_RETRY.
1611 *
1612 * This is meant to be called in the specific scenario where for locking reasons
1613 * we try to access user memory in atomic context (within a pagefault_disable()
1614 * section), this returns -EFAULT, and we want to resolve the user fault before
1615 * trying again.
1616 *
1617 * Typically this is meant to be used by the futex code.
1618 *
1619 * The main difference with get_user_pages() is that this function will
1620 * unconditionally call handle_mm_fault() which will in turn perform all the
1621 * necessary SW fixup of the dirty and young bits in the PTE, while
1622 * get_user_pages() only guarantees to update these in the struct page.
1623 *
1624 * This is important for some architectures where those bits also gate the
1625 * access permission to the page because they are maintained in software.  On
1626 * such architectures, gup() will not be enough to make a subsequent access
1627 * succeed.
1628 *
1629 * This function will not return with an unlocked mmap_lock. So it has not the
1630 * same semantics wrt the @mm->mmap_lock as does filemap_fault().
1631 */
1632int fixup_user_fault(struct mm_struct *mm,
1633		     unsigned long address, unsigned int fault_flags,
1634		     bool *unlocked)
1635{
1636	struct vm_area_struct *vma;
1637	vm_fault_t ret;
1638
1639	address = untagged_addr_remote(mm, address);
1640
1641	if (unlocked)
1642		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1643
1644retry:
1645	vma = gup_vma_lookup(mm, address);
1646	if (!vma)
1647		return -EFAULT;
1648
1649	if (!vma_permits_fault(vma, fault_flags))
1650		return -EFAULT;
1651
1652	if ((fault_flags & FAULT_FLAG_KILLABLE) &&
1653	    fatal_signal_pending(current))
1654		return -EINTR;
1655
1656	ret = handle_mm_fault(vma, address, fault_flags, NULL);
1657
1658	if (ret & VM_FAULT_COMPLETED) {
1659		/*
1660		 * NOTE: it's a pity that we need to retake the lock here
1661		 * to pair with the unlock() in the callers. Ideally we
1662		 * could tell the callers so they do not need to unlock.
1663		 */
1664		mmap_read_lock(mm);
1665		*unlocked = true;
1666		return 0;
1667	}
1668
1669	if (ret & VM_FAULT_ERROR) {
1670		int err = vm_fault_to_errno(ret, 0);
1671
1672		if (err)
1673			return err;
1674		BUG();
1675	}
1676
1677	if (ret & VM_FAULT_RETRY) {
1678		mmap_read_lock(mm);
1679		*unlocked = true;
1680		fault_flags |= FAULT_FLAG_TRIED;
1681		goto retry;
1682	}
1683
1684	return 0;
1685}
1686EXPORT_SYMBOL_GPL(fixup_user_fault);
1687
1688/*
1689 * GUP always responds to fatal signals.  When FOLL_INTERRUPTIBLE is
1690 * specified, it'll also respond to generic signals.  The caller of GUP
1691 * that has FOLL_INTERRUPTIBLE should take care of the GUP interruption.
1692 */
1693static bool gup_signal_pending(unsigned int flags)
1694{
1695	if (fatal_signal_pending(current))
1696		return true;
1697
1698	if (!(flags & FOLL_INTERRUPTIBLE))
1699		return false;
1700
1701	return signal_pending(current);
1702}
1703
1704/*
1705 * Locking: (*locked == 1) means that the mmap_lock has already been acquired by
1706 * the caller. This function may drop the mmap_lock. If it does so, then it will
1707 * set (*locked = 0).
1708 *
1709 * (*locked == 0) means that the caller expects this function to acquire and
1710 * drop the mmap_lock. Therefore, the value of *locked will still be zero when
1711 * the function returns, even though it may have changed temporarily during
1712 * function execution.
1713 *
1714 * Please note that this function, unlike __get_user_pages(), will not return 0
1715 * for nr_pages > 0, unless FOLL_NOWAIT is used.
1716 */
1717static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
1718						unsigned long start,
1719						unsigned long nr_pages,
1720						struct page **pages,
1721						int *locked,
1722						unsigned int flags)
1723{
1724	long ret, pages_done;
1725	bool must_unlock = false;
1726
1727	if (!nr_pages)
1728		return 0;
1729
1730	/*
1731	 * The internal caller expects GUP to manage the lock internally and the
1732	 * lock must be released when this returns.
1733	 */
1734	if (!*locked) {
1735		if (mmap_read_lock_killable(mm))
1736			return -EAGAIN;
1737		must_unlock = true;
1738		*locked = 1;
1739	}
1740	else
1741		mmap_assert_locked(mm);
1742
1743	if (flags & FOLL_PIN)
1744		mm_set_has_pinned_flag(&mm->flags);
1745
1746	/*
1747	 * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior
1748	 * is to set FOLL_GET if the caller wants pages[] filled in (but has
1749	 * carelessly failed to specify FOLL_GET), so keep doing that, but only
1750	 * for FOLL_GET, not for the newer FOLL_PIN.
1751	 *
1752	 * FOLL_PIN always expects pages to be non-null, but no need to assert
1753	 * that here, as any failures will be obvious enough.
1754	 */
1755	if (pages && !(flags & FOLL_PIN))
1756		flags |= FOLL_GET;
1757
1758	pages_done = 0;
1759	for (;;) {
1760		ret = __get_user_pages(mm, start, nr_pages, flags, pages,
1761				       locked);
1762		if (!(flags & FOLL_UNLOCKABLE)) {
1763			/* VM_FAULT_RETRY couldn't trigger, bypass */
1764			pages_done = ret;
1765			break;
1766		}
1767
1768		/* VM_FAULT_RETRY or VM_FAULT_COMPLETED cannot return errors */
1769		if (!*locked) {
1770			BUG_ON(ret < 0);
1771			BUG_ON(ret >= nr_pages);
1772		}
1773
1774		if (ret > 0) {
1775			nr_pages -= ret;
1776			pages_done += ret;
1777			if (!nr_pages)
1778				break;
1779		}
1780		if (*locked) {
1781			/*
1782			 * VM_FAULT_RETRY didn't trigger or it was a
1783			 * FOLL_NOWAIT.
1784			 */
1785			if (!pages_done)
1786				pages_done = ret;
1787			break;
1788		}
1789		/*
1790		 * VM_FAULT_RETRY triggered, so seek to the faulting offset.
1791		 * For the prefault case (!pages) we only update counts.
1792		 */
1793		if (likely(pages))
1794			pages += ret;
1795		start += ret << PAGE_SHIFT;
1796
1797		/* The lock was temporarily dropped, so we must unlock later */
1798		must_unlock = true;
1799
1800retry:
1801		/*
1802		 * Repeat on the address that fired VM_FAULT_RETRY
1803		 * with both FAULT_FLAG_ALLOW_RETRY and
1804		 * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
1805		 * by fatal signals of even common signals, depending on
1806		 * the caller's request. So we need to check it before we
1807		 * start trying again otherwise it can loop forever.
1808		 */
1809		if (gup_signal_pending(flags)) {
1810			if (!pages_done)
1811				pages_done = -EINTR;
1812			break;
1813		}
1814
1815		ret = mmap_read_lock_killable(mm);
1816		if (ret) {
1817			BUG_ON(ret > 0);
1818			if (!pages_done)
1819				pages_done = ret;
1820			break;
1821		}
1822
1823		*locked = 1;
1824		ret = __get_user_pages(mm, start, 1, flags | FOLL_TRIED,
1825				       pages, locked);
1826		if (!*locked) {
1827			/* Continue to retry until we succeeded */
1828			BUG_ON(ret != 0);
1829			goto retry;
1830		}
1831		if (ret != 1) {
1832			BUG_ON(ret > 1);
1833			if (!pages_done)
1834				pages_done = ret;
1835			break;
1836		}
1837		nr_pages--;
1838		pages_done++;
1839		if (!nr_pages)
1840			break;
1841		if (likely(pages))
1842			pages++;
1843		start += PAGE_SIZE;
1844	}
1845	if (must_unlock && *locked) {
1846		/*
1847		 * We either temporarily dropped the lock, or the caller
1848		 * requested that we both acquire and drop the lock. Either way,
1849		 * we must now unlock, and notify the caller of that state.
1850		 */
1851		mmap_read_unlock(mm);
1852		*locked = 0;
1853	}
1854
1855	/*
1856	 * Failing to pin anything implies something has gone wrong (except when
1857	 * FOLL_NOWAIT is specified).
1858	 */
1859	if (WARN_ON_ONCE(pages_done == 0 && !(flags & FOLL_NOWAIT)))
1860		return -EFAULT;
1861
1862	return pages_done;
1863}
1864
1865/**
1866 * populate_vma_page_range() -  populate a range of pages in the vma.
1867 * @vma:   target vma
1868 * @start: start address
1869 * @end:   end address
1870 * @locked: whether the mmap_lock is still held
1871 *
1872 * This takes care of mlocking the pages too if VM_LOCKED is set.
1873 *
1874 * Return either number of pages pinned in the vma, or a negative error
1875 * code on error.
1876 *
1877 * vma->vm_mm->mmap_lock must be held.
1878 *
1879 * If @locked is NULL, it may be held for read or write and will
1880 * be unperturbed.
1881 *
1882 * If @locked is non-NULL, it must held for read only and may be
1883 * released.  If it's released, *@locked will be set to 0.
1884 */
1885long populate_vma_page_range(struct vm_area_struct *vma,
1886		unsigned long start, unsigned long end, int *locked)
1887{
1888	struct mm_struct *mm = vma->vm_mm;
1889	unsigned long nr_pages = (end - start) / PAGE_SIZE;
1890	int local_locked = 1;
1891	int gup_flags;
1892	long ret;
1893
1894	VM_BUG_ON(!PAGE_ALIGNED(start));
1895	VM_BUG_ON(!PAGE_ALIGNED(end));
1896	VM_BUG_ON_VMA(start < vma->vm_start, vma);
1897	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
1898	mmap_assert_locked(mm);
1899
1900	/*
1901	 * Rightly or wrongly, the VM_LOCKONFAULT case has never used
1902	 * faultin_page() to break COW, so it has no work to do here.
1903	 */
1904	if (vma->vm_flags & VM_LOCKONFAULT)
1905		return nr_pages;
1906
1907	/* ... similarly, we've never faulted in PROT_NONE pages */
1908	if (!vma_is_accessible(vma))
1909		return -EFAULT;
1910
1911	gup_flags = FOLL_TOUCH;
1912	/*
1913	 * We want to touch writable mappings with a write fault in order
1914	 * to break COW, except for shared mappings because these don't COW
1915	 * and we would not want to dirty them for nothing.
1916	 *
1917	 * Otherwise, do a read fault, and use FOLL_FORCE in case it's not
1918	 * readable (ie write-only or executable).
1919	 */
1920	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
1921		gup_flags |= FOLL_WRITE;
1922	else
1923		gup_flags |= FOLL_FORCE;
1924
1925	if (locked)
1926		gup_flags |= FOLL_UNLOCKABLE;
1927
1928	/*
1929	 * We made sure addr is within a VMA, so the following will
1930	 * not result in a stack expansion that recurses back here.
1931	 */
1932	ret = __get_user_pages(mm, start, nr_pages, gup_flags,
1933			       NULL, locked ? locked : &local_locked);
1934	lru_add_drain();
1935	return ret;
1936}
1937
1938/*
1939 * faultin_page_range() - populate (prefault) page tables inside the
1940 *			  given range readable/writable
1941 *
1942 * This takes care of mlocking the pages, too, if VM_LOCKED is set.
1943 *
1944 * @mm: the mm to populate page tables in
1945 * @start: start address
1946 * @end: end address
1947 * @write: whether to prefault readable or writable
1948 * @locked: whether the mmap_lock is still held
1949 *
1950 * Returns either number of processed pages in the MM, or a negative error
1951 * code on error (see __get_user_pages()). Note that this function reports
1952 * errors related to VMAs, such as incompatible mappings, as expected by
1953 * MADV_POPULATE_(READ|WRITE).
1954 *
1955 * The range must be page-aligned.
1956 *
1957 * mm->mmap_lock must be held. If it's released, *@locked will be set to 0.
1958 */
1959long faultin_page_range(struct mm_struct *mm, unsigned long start,
1960			unsigned long end, bool write, int *locked)
1961{
1962	unsigned long nr_pages = (end - start) / PAGE_SIZE;
1963	int gup_flags;
1964	long ret;
1965
1966	VM_BUG_ON(!PAGE_ALIGNED(start));
1967	VM_BUG_ON(!PAGE_ALIGNED(end));
1968	mmap_assert_locked(mm);
1969
1970	/*
1971	 * FOLL_TOUCH: Mark page accessed and thereby young; will also mark
1972	 *	       the page dirty with FOLL_WRITE -- which doesn't make a
1973	 *	       difference with !FOLL_FORCE, because the page is writable
1974	 *	       in the page table.
1975	 * FOLL_HWPOISON: Return -EHWPOISON instead of -EFAULT when we hit
1976	 *		  a poisoned page.
1977	 * !FOLL_FORCE: Require proper access permissions.
1978	 */
1979	gup_flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_UNLOCKABLE |
1980		    FOLL_MADV_POPULATE;
1981	if (write)
1982		gup_flags |= FOLL_WRITE;
1983
1984	ret = __get_user_pages_locked(mm, start, nr_pages, NULL, locked,
1985				      gup_flags);
1986	lru_add_drain();
1987	return ret;
1988}
1989
1990/*
1991 * __mm_populate - populate and/or mlock pages within a range of address space.
1992 *
1993 * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
1994 * flags. VMAs must be already marked with the desired vm_flags, and
1995 * mmap_lock must not be held.
1996 */
1997int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
1998{
1999	struct mm_struct *mm = current->mm;
2000	unsigned long end, nstart, nend;
2001	struct vm_area_struct *vma = NULL;
2002	int locked = 0;
2003	long ret = 0;
2004
2005	end = start + len;
2006
2007	for (nstart = start; nstart < end; nstart = nend) {
2008		/*
2009		 * We want to fault in pages for [nstart; end) address range.
2010		 * Find first corresponding VMA.
2011		 */
2012		if (!locked) {
2013			locked = 1;
2014			mmap_read_lock(mm);
2015			vma = find_vma_intersection(mm, nstart, end);
2016		} else if (nstart >= vma->vm_end)
2017			vma = find_vma_intersection(mm, vma->vm_end, end);
2018
2019		if (!vma)
2020			break;
2021		/*
2022		 * Set [nstart; nend) to intersection of desired address
2023		 * range with the first VMA. Also, skip undesirable VMA types.
2024		 */
2025		nend = min(end, vma->vm_end);
2026		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
2027			continue;
2028		if (nstart < vma->vm_start)
2029			nstart = vma->vm_start;
2030		/*
2031		 * Now fault in a range of pages. populate_vma_page_range()
2032		 * double checks the vma flags, so that it won't mlock pages
2033		 * if the vma was already munlocked.
2034		 */
2035		ret = populate_vma_page_range(vma, nstart, nend, &locked);
2036		if (ret < 0) {
2037			if (ignore_errors) {
2038				ret = 0;
2039				continue;	/* continue at next VMA */
2040			}
2041			break;
2042		}
2043		nend = nstart + ret * PAGE_SIZE;
2044		ret = 0;
2045	}
2046	if (locked)
2047		mmap_read_unlock(mm);
2048	return ret;	/* 0 or negative error code */
2049}
2050#else /* CONFIG_MMU */
2051static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
2052		unsigned long nr_pages, struct page **pages,
2053		int *locked, unsigned int foll_flags)
2054{
2055	struct vm_area_struct *vma;
2056	bool must_unlock = false;
2057	unsigned long vm_flags;
2058	long i;
2059
2060	if (!nr_pages)
2061		return 0;
2062
2063	/*
2064	 * The internal caller expects GUP to manage the lock internally and the
2065	 * lock must be released when this returns.
2066	 */
2067	if (!*locked) {
2068		if (mmap_read_lock_killable(mm))
2069			return -EAGAIN;
2070		must_unlock = true;
2071		*locked = 1;
2072	}
2073
2074	/* calculate required read or write permissions.
2075	 * If FOLL_FORCE is set, we only require the "MAY" flags.
2076	 */
2077	vm_flags  = (foll_flags & FOLL_WRITE) ?
2078			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
2079	vm_flags &= (foll_flags & FOLL_FORCE) ?
2080			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
2081
2082	for (i = 0; i < nr_pages; i++) {
2083		vma = find_vma(mm, start);
2084		if (!vma)
2085			break;
2086
2087		/* protect what we can, including chardevs */
2088		if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
2089		    !(vm_flags & vma->vm_flags))
2090			break;
2091
2092		if (pages) {
2093			pages[i] = virt_to_page((void *)start);
2094			if (pages[i])
2095				get_page(pages[i]);
2096		}
2097
2098		start = (start + PAGE_SIZE) & PAGE_MASK;
2099	}
2100
2101	if (must_unlock && *locked) {
2102		mmap_read_unlock(mm);
2103		*locked = 0;
2104	}
2105
2106	return i ? : -EFAULT;
2107}
2108#endif /* !CONFIG_MMU */
2109
2110/**
2111 * fault_in_writeable - fault in userspace address range for writing
2112 * @uaddr: start of address range
2113 * @size: size of address range
2114 *
2115 * Returns the number of bytes not faulted in (like copy_to_user() and
2116 * copy_from_user()).
2117 */
2118size_t fault_in_writeable(char __user *uaddr, size_t size)
2119{
2120	char __user *start = uaddr, *end;
2121
2122	if (unlikely(size == 0))
2123		return 0;
2124	if (!user_write_access_begin(uaddr, size))
2125		return size;
2126	if (!PAGE_ALIGNED(uaddr)) {
2127		unsafe_put_user(0, uaddr, out);
2128		uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);
2129	}
2130	end = (char __user *)PAGE_ALIGN((unsigned long)start + size);
2131	if (unlikely(end < start))
2132		end = NULL;
2133	while (uaddr != end) {
2134		unsafe_put_user(0, uaddr, out);
2135		uaddr += PAGE_SIZE;
2136	}
2137
2138out:
2139	user_write_access_end();
2140	if (size > uaddr - start)
2141		return size - (uaddr - start);
2142	return 0;
2143}
2144EXPORT_SYMBOL(fault_in_writeable);
2145
2146/**
2147 * fault_in_subpage_writeable - fault in an address range for writing
2148 * @uaddr: start of address range
2149 * @size: size of address range
2150 *
2151 * Fault in a user address range for writing while checking for permissions at
2152 * sub-page granularity (e.g. arm64 MTE). This function should be used when
2153 * the caller cannot guarantee forward progress of a copy_to_user() loop.
2154 *
2155 * Returns the number of bytes not faulted in (like copy_to_user() and
2156 * copy_from_user()).
2157 */
2158size_t fault_in_subpage_writeable(char __user *uaddr, size_t size)
2159{
2160	size_t faulted_in;
2161
2162	/*
2163	 * Attempt faulting in at page granularity first for page table
2164	 * permission checking. The arch-specific probe_subpage_writeable()
2165	 * functions may not check for this.
2166	 */
2167	faulted_in = size - fault_in_writeable(uaddr, size);
2168	if (faulted_in)
2169		faulted_in -= probe_subpage_writeable(uaddr, faulted_in);
2170
2171	return size - faulted_in;
2172}
2173EXPORT_SYMBOL(fault_in_subpage_writeable);
2174
2175/*
2176 * fault_in_safe_writeable - fault in an address range for writing
2177 * @uaddr: start of address range
2178 * @size: length of address range
2179 *
2180 * Faults in an address range for writing.  This is primarily useful when we
2181 * already know that some or all of the pages in the address range aren't in
2182 * memory.
2183 *
2184 * Unlike fault_in_writeable(), this function is non-destructive.
2185 *
2186 * Note that we don't pin or otherwise hold the pages referenced that we fault
2187 * in.  There's no guarantee that they'll stay in memory for any duration of
2188 * time.
2189 *
2190 * Returns the number of bytes not faulted in, like copy_to_user() and
2191 * copy_from_user().
2192 */
2193size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
2194{
2195	unsigned long start = (unsigned long)uaddr, end;
2196	struct mm_struct *mm = current->mm;
2197	bool unlocked = false;
2198
2199	if (unlikely(size == 0))
2200		return 0;
2201	end = PAGE_ALIGN(start + size);
2202	if (end < start)
2203		end = 0;
2204
2205	mmap_read_lock(mm);
2206	do {
2207		if (fixup_user_fault(mm, start, FAULT_FLAG_WRITE, &unlocked))
2208			break;
2209		start = (start + PAGE_SIZE) & PAGE_MASK;
2210	} while (start != end);
2211	mmap_read_unlock(mm);
2212
2213	if (size > (unsigned long)uaddr - start)
2214		return size - ((unsigned long)uaddr - start);
2215	return 0;
2216}
2217EXPORT_SYMBOL(fault_in_safe_writeable);
2218
2219/**
2220 * fault_in_readable - fault in userspace address range for reading
2221 * @uaddr: start of user address range
2222 * @size: size of user address range
2223 *
2224 * Returns the number of bytes not faulted in (like copy_to_user() and
2225 * copy_from_user()).
2226 */
2227size_t fault_in_readable(const char __user *uaddr, size_t size)
2228{
2229	const char __user *start = uaddr, *end;
2230	volatile char c;
2231
2232	if (unlikely(size == 0))
2233		return 0;
2234	if (!user_read_access_begin(uaddr, size))
2235		return size;
2236	if (!PAGE_ALIGNED(uaddr)) {
2237		unsafe_get_user(c, uaddr, out);
2238		uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
2239	}
2240	end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
2241	if (unlikely(end < start))
2242		end = NULL;
2243	while (uaddr != end) {
2244		unsafe_get_user(c, uaddr, out);
2245		uaddr += PAGE_SIZE;
2246	}
2247
2248out:
2249	user_read_access_end();
2250	(void)c;
2251	if (size > uaddr - start)
2252		return size - (uaddr - start);
2253	return 0;
2254}
2255EXPORT_SYMBOL(fault_in_readable);
2256
2257/**
2258 * get_dump_page() - pin user page in memory while writing it to core dump
2259 * @addr: user address
2260 *
2261 * Returns struct page pointer of user page pinned for dump,
2262 * to be freed afterwards by put_page().
2263 *
2264 * Returns NULL on any kind of failure - a hole must then be inserted into
2265 * the corefile, to preserve alignment with its headers; and also returns
2266 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
2267 * allowing a hole to be left in the corefile to save disk space.
2268 *
2269 * Called without mmap_lock (takes and releases the mmap_lock by itself).
2270 */
2271#ifdef CONFIG_ELF_CORE
2272struct page *get_dump_page(unsigned long addr)
2273{
2274	struct page *page;
2275	int locked = 0;
2276	int ret;
2277
2278	ret = __get_user_pages_locked(current->mm, addr, 1, &page, &locked,
2279				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
2280	return (ret == 1) ? page : NULL;
2281}
2282#endif /* CONFIG_ELF_CORE */
2283
2284#ifdef CONFIG_MIGRATION
2285
2286/*
2287 * An array of either pages or folios ("pofs"). Although it may seem tempting to
2288 * avoid this complication, by simply interpreting a list of folios as a list of
2289 * pages, that approach won't work in the longer term, because eventually the
2290 * layouts of struct page and struct folio will become completely different.
2291 * Furthermore, this pof approach avoids excessive page_folio() calls.
2292 */
2293struct pages_or_folios {
2294	union {
2295		struct page **pages;
2296		struct folio **folios;
2297		void **entries;
2298	};
2299	bool has_folios;
2300	long nr_entries;
2301};
2302
2303static struct folio *pofs_get_folio(struct pages_or_folios *pofs, long i)
2304{
2305	if (pofs->has_folios)
2306		return pofs->folios[i];
2307	return page_folio(pofs->pages[i]);
2308}
2309
2310static void pofs_clear_entry(struct pages_or_folios *pofs, long i)
2311{
2312	pofs->entries[i] = NULL;
2313}
2314
2315static void pofs_unpin(struct pages_or_folios *pofs)
2316{
2317	if (pofs->has_folios)
2318		unpin_folios(pofs->folios, pofs->nr_entries);
2319	else
2320		unpin_user_pages(pofs->pages, pofs->nr_entries);
2321}
2322
2323/*
2324 * Returns the number of collected folios. Return value is always >= 0.
2325 */
2326static void collect_longterm_unpinnable_folios(
2327		struct list_head *movable_folio_list,
2328		struct pages_or_folios *pofs)
2329{
2330	struct folio *prev_folio = NULL;
2331	bool drain_allow = true;
2332	unsigned long i;
2333
2334	for (i = 0; i < pofs->nr_entries; i++) {
2335		struct folio *folio = pofs_get_folio(pofs, i);
2336
2337		if (folio == prev_folio)
2338			continue;
2339		prev_folio = folio;
2340
2341		if (folio_is_longterm_pinnable(folio))
2342			continue;
2343
2344		if (folio_is_device_coherent(folio))
2345			continue;
2346
2347		if (folio_test_hugetlb(folio)) {
2348			isolate_hugetlb(folio, movable_folio_list);
2349			continue;
2350		}
2351
2352		if (!folio_test_lru(folio) && drain_allow) {
2353			lru_add_drain_all();
2354			drain_allow = false;
2355		}
2356
2357		if (!folio_isolate_lru(folio))
2358			continue;
2359
2360		list_add_tail(&folio->lru, movable_folio_list);
2361		node_stat_mod_folio(folio,
2362				    NR_ISOLATED_ANON + folio_is_file_lru(folio),
2363				    folio_nr_pages(folio));
2364	}
2365}
2366
2367/*
2368 * Unpins all folios and migrates device coherent folios and movable_folio_list.
2369 * Returns -EAGAIN if all folios were successfully migrated or -errno for
2370 * failure (or partial success).
2371 */
2372static int
2373migrate_longterm_unpinnable_folios(struct list_head *movable_folio_list,
2374				   struct pages_or_folios *pofs)
2375{
2376	int ret;
2377	unsigned long i;
2378
2379	for (i = 0; i < pofs->nr_entries; i++) {
2380		struct folio *folio = pofs_get_folio(pofs, i);
2381
2382		if (folio_is_device_coherent(folio)) {
2383			/*
2384			 * Migration will fail if the folio is pinned, so
2385			 * convert the pin on the source folio to a normal
2386			 * reference.
2387			 */
2388			pofs_clear_entry(pofs, i);
2389			folio_get(folio);
2390			gup_put_folio(folio, 1, FOLL_PIN);
2391
2392			if (migrate_device_coherent_folio(folio)) {
2393				ret = -EBUSY;
2394				goto err;
2395			}
2396
2397			continue;
2398		}
2399
2400		/*
2401		 * We can't migrate folios with unexpected references, so drop
2402		 * the reference obtained by __get_user_pages_locked().
2403		 * Migrating folios have been added to movable_folio_list after
2404		 * calling folio_isolate_lru() which takes a reference so the
2405		 * folio won't be freed if it's migrating.
2406		 */
2407		unpin_folio(folio);
2408		pofs_clear_entry(pofs, i);
2409	}
2410
2411	if (!list_empty(movable_folio_list)) {
2412		struct migration_target_control mtc = {
2413			.nid = NUMA_NO_NODE,
2414			.gfp_mask = GFP_USER | __GFP_NOWARN,
2415			.reason = MR_LONGTERM_PIN,
2416		};
2417
2418		if (migrate_pages(movable_folio_list, alloc_migration_target,
2419				  NULL, (unsigned long)&mtc, MIGRATE_SYNC,
2420				  MR_LONGTERM_PIN, NULL)) {
2421			ret = -ENOMEM;
2422			goto err;
2423		}
2424	}
2425
2426	putback_movable_pages(movable_folio_list);
2427
2428	return -EAGAIN;
2429
2430err:
2431	pofs_unpin(pofs);
2432	putback_movable_pages(movable_folio_list);
2433
2434	return ret;
2435}
2436
2437static long
2438check_and_migrate_movable_pages_or_folios(struct pages_or_folios *pofs)
2439{
2440	LIST_HEAD(movable_folio_list);
2441
2442	collect_longterm_unpinnable_folios(&movable_folio_list, pofs);
2443	if (list_empty(&movable_folio_list))
2444		return 0;
2445
2446	return migrate_longterm_unpinnable_folios(&movable_folio_list, pofs);
2447}
2448
2449/*
2450 * Check whether all folios are *allowed* to be pinned indefinitely (long term).
2451 * Rather confusingly, all folios in the range are required to be pinned via
2452 * FOLL_PIN, before calling this routine.
2453 *
2454 * Return values:
2455 *
2456 * 0: if everything is OK and all folios in the range are allowed to be pinned,
2457 * then this routine leaves all folios pinned and returns zero for success.
2458 *
2459 * -EAGAIN: if any folios in the range are not allowed to be pinned, then this
2460 * routine will migrate those folios away, unpin all the folios in the range. If
2461 * migration of the entire set of folios succeeds, then -EAGAIN is returned. The
2462 * caller should re-pin the entire range with FOLL_PIN and then call this
2463 * routine again.
2464 *
2465 * -ENOMEM, or any other -errno: if an error *other* than -EAGAIN occurs, this
2466 * indicates a migration failure. The caller should give up, and propagate the
2467 * error back up the call stack. The caller does not need to unpin any folios in
2468 * that case, because this routine will do the unpinning.
2469 */
2470static long check_and_migrate_movable_folios(unsigned long nr_folios,
2471					     struct folio **folios)
2472{
2473	struct pages_or_folios pofs = {
2474		.folios = folios,
2475		.has_folios = true,
2476		.nr_entries = nr_folios,
2477	};
2478
2479	return check_and_migrate_movable_pages_or_folios(&pofs);
2480}
2481
2482/*
2483 * Return values and behavior are the same as those for
2484 * check_and_migrate_movable_folios().
2485 */
2486static long check_and_migrate_movable_pages(unsigned long nr_pages,
2487					    struct page **pages)
2488{
2489	struct pages_or_folios pofs = {
2490		.pages = pages,
2491		.has_folios = false,
2492		.nr_entries = nr_pages,
2493	};
2494
2495	return check_and_migrate_movable_pages_or_folios(&pofs);
2496}
2497#else
2498static long check_and_migrate_movable_pages(unsigned long nr_pages,
2499					    struct page **pages)
2500{
2501	return 0;
2502}
2503
2504static long check_and_migrate_movable_folios(unsigned long nr_folios,
2505					     struct folio **folios)
2506{
2507	return 0;
2508}
2509#endif /* CONFIG_MIGRATION */
2510
2511/*
2512 * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
2513 * allows us to process the FOLL_LONGTERM flag.
2514 */
2515static long __gup_longterm_locked(struct mm_struct *mm,
2516				  unsigned long start,
2517				  unsigned long nr_pages,
2518				  struct page **pages,
2519				  int *locked,
2520				  unsigned int gup_flags)
2521{
2522	unsigned int flags;
2523	long rc, nr_pinned_pages;
2524
2525	if (!(gup_flags & FOLL_LONGTERM))
2526		return __get_user_pages_locked(mm, start, nr_pages, pages,
2527					       locked, gup_flags);
2528
2529	flags = memalloc_pin_save();
2530	do {
2531		nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages,
2532							  pages, locked,
2533							  gup_flags);
2534		if (nr_pinned_pages <= 0) {
2535			rc = nr_pinned_pages;
2536			break;
2537		}
2538
2539		/* FOLL_LONGTERM implies FOLL_PIN */
2540		rc = check_and_migrate_movable_pages(nr_pinned_pages, pages);
2541	} while (rc == -EAGAIN);
2542	memalloc_pin_restore(flags);
2543	return rc ? rc : nr_pinned_pages;
2544}
2545
2546/*
2547 * Check that the given flags are valid for the exported gup/pup interface, and
2548 * update them with the required flags that the caller must have set.
2549 */
2550static bool is_valid_gup_args(struct page **pages, int *locked,
2551			      unsigned int *gup_flags_p, unsigned int to_set)
2552{
2553	unsigned int gup_flags = *gup_flags_p;
2554
2555	/*
2556	 * These flags not allowed to be specified externally to the gup
2557	 * interfaces:
2558	 * - FOLL_TOUCH/FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
2559	 * - FOLL_REMOTE is internal only, set in (get|pin)_user_pages_remote()
2560	 * - FOLL_UNLOCKABLE is internal only and used if locked is !NULL
2561	 */
2562	if (WARN_ON_ONCE(gup_flags & INTERNAL_GUP_FLAGS))
2563		return false;
2564
2565	gup_flags |= to_set;
2566	if (locked) {
2567		/* At the external interface locked must be set */
2568		if (WARN_ON_ONCE(*locked != 1))
2569			return false;
2570
2571		gup_flags |= FOLL_UNLOCKABLE;
2572	}
2573
2574	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
2575	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
2576			 (FOLL_PIN | FOLL_GET)))
2577		return false;
2578
2579	/* LONGTERM can only be specified when pinning */
2580	if (WARN_ON_ONCE(!(gup_flags & FOLL_PIN) && (gup_flags & FOLL_LONGTERM)))
2581		return false;
2582
2583	/* Pages input must be given if using GET/PIN */
2584	if (WARN_ON_ONCE((gup_flags & (FOLL_GET | FOLL_PIN)) && !pages))
2585		return false;
2586
2587	/* We want to allow the pgmap to be hot-unplugged at all times */
2588	if (WARN_ON_ONCE((gup_flags & FOLL_LONGTERM) &&
2589			 (gup_flags & FOLL_PCI_P2PDMA)))
2590		return false;
2591
2592	*gup_flags_p = gup_flags;
2593	return true;
2594}
2595
2596#ifdef CONFIG_MMU
2597/**
2598 * get_user_pages_remote() - pin user pages in memory
2599 * @mm:		mm_struct of target mm
2600 * @start:	starting user address
2601 * @nr_pages:	number of pages from start to pin
2602 * @gup_flags:	flags modifying lookup behaviour
2603 * @pages:	array that receives pointers to the pages pinned.
2604 *		Should be at least nr_pages long. Or NULL, if caller
2605 *		only intends to ensure the pages are faulted in.
2606 * @locked:	pointer to lock flag indicating whether lock is held and
2607 *		subsequently whether VM_FAULT_RETRY functionality can be
2608 *		utilised. Lock must initially be held.
2609 *
2610 * Returns either number of pages pinned (which may be less than the
2611 * number requested), or an error. Details about the return value:
2612 *
2613 * -- If nr_pages is 0, returns 0.
2614 * -- If nr_pages is >0, but no pages were pinned, returns -errno.
2615 * -- If nr_pages is >0, and some pages were pinned, returns the number of
2616 *    pages pinned. Again, this may be less than nr_pages.
2617 *
2618 * The caller is responsible for releasing returned @pages, via put_page().
2619 *
2620 * Must be called with mmap_lock held for read or write.
2621 *
2622 * get_user_pages_remote walks a process's page tables and takes a reference
2623 * to each struct page that each user address corresponds to at a given
2624 * instant. That is, it takes the page that would be accessed if a user
2625 * thread accesses the given user virtual address at that instant.
2626 *
2627 * This does not guarantee that the page exists in the user mappings when
2628 * get_user_pages_remote returns, and there may even be a completely different
2629 * page there in some cases (eg. if mmapped pagecache has been invalidated
2630 * and subsequently re-faulted). However it does guarantee that the page
2631 * won't be freed completely. And mostly callers simply care that the page
2632 * contains data that was valid *at some point in time*. Typically, an IO
2633 * or similar operation cannot guarantee anything stronger anyway because
2634 * locks can't be held over the syscall boundary.
2635 *
2636 * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
2637 * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
2638 * be called after the page is finished with, and before put_page is called.
2639 *
2640 * get_user_pages_remote is typically used for fewer-copy IO operations,
2641 * to get a handle on the memory by some means other than accesses
2642 * via the user virtual addresses. The pages may be submitted for
2643 * DMA to devices or accessed via their kernel linear mapping (via the
2644 * kmap APIs). Care should be taken to use the correct cache flushing APIs.
2645 *
2646 * See also get_user_pages_fast, for performance critical applications.
2647 *
2648 * get_user_pages_remote should be phased out in favor of
2649 * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
2650 * should use get_user_pages_remote because it cannot pass
2651 * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
2652 */
2653long get_user_pages_remote(struct mm_struct *mm,
2654		unsigned long start, unsigned long nr_pages,
2655		unsigned int gup_flags, struct page **pages,
2656		int *locked)
2657{
2658	int local_locked = 1;
2659
2660	if (!is_valid_gup_args(pages, locked, &gup_flags,
2661			       FOLL_TOUCH | FOLL_REMOTE))
2662		return -EINVAL;
2663
2664	return __get_user_pages_locked(mm, start, nr_pages, pages,
2665				       locked ? locked : &local_locked,
2666				       gup_flags);
2667}
2668EXPORT_SYMBOL(get_user_pages_remote);
2669
2670#else /* CONFIG_MMU */
2671long get_user_pages_remote(struct mm_struct *mm,
2672			   unsigned long start, unsigned long nr_pages,
2673			   unsigned int gup_flags, struct page **pages,
2674			   int *locked)
2675{
2676	return 0;
2677}
2678#endif /* !CONFIG_MMU */
2679
2680/**
2681 * get_user_pages() - pin user pages in memory
2682 * @start:      starting user address
2683 * @nr_pages:   number of pages from start to pin
2684 * @gup_flags:  flags modifying lookup behaviour
2685 * @pages:      array that receives pointers to the pages pinned.
2686 *              Should be at least nr_pages long. Or NULL, if caller
2687 *              only intends to ensure the pages are faulted in.
2688 *
2689 * This is the same as get_user_pages_remote(), just with a less-flexible
2690 * calling convention where we assume that the mm being operated on belongs to
2691 * the current task, and doesn't allow passing of a locked parameter.  We also
2692 * obviously don't pass FOLL_REMOTE in here.
2693 */
2694long get_user_pages(unsigned long start, unsigned long nr_pages,
2695		    unsigned int gup_flags, struct page **pages)
2696{
2697	int locked = 1;
2698
2699	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_TOUCH))
2700		return -EINVAL;
2701
2702	return __get_user_pages_locked(current->mm, start, nr_pages, pages,
2703				       &locked, gup_flags);
2704}
2705EXPORT_SYMBOL(get_user_pages);
2706
2707/*
2708 * get_user_pages_unlocked() is suitable to replace the form:
2709 *
2710 *      mmap_read_lock(mm);
2711 *      get_user_pages(mm, ..., pages, NULL);
2712 *      mmap_read_unlock(mm);
2713 *
2714 *  with:
2715 *
2716 *      get_user_pages_unlocked(mm, ..., pages);
2717 *
2718 * It is functionally equivalent to get_user_pages_fast so
2719 * get_user_pages_fast should be used instead if specific gup_flags
2720 * (e.g. FOLL_FORCE) are not required.
2721 */
2722long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
2723			     struct page **pages, unsigned int gup_flags)
2724{
2725	int locked = 0;
2726
2727	if (!is_valid_gup_args(pages, NULL, &gup_flags,
2728			       FOLL_TOUCH | FOLL_UNLOCKABLE))
2729		return -EINVAL;
2730
2731	return __get_user_pages_locked(current->mm, start, nr_pages, pages,
2732				       &locked, gup_flags);
2733}
2734EXPORT_SYMBOL(get_user_pages_unlocked);
2735
2736/*
2737 * GUP-fast
2738 *
2739 * get_user_pages_fast attempts to pin user pages by walking the page
2740 * tables directly and avoids taking locks. Thus the walker needs to be
2741 * protected from page table pages being freed from under it, and should
2742 * block any THP splits.
2743 *
2744 * One way to achieve this is to have the walker disable interrupts, and
2745 * rely on IPIs from the TLB flushing code blocking before the page table
2746 * pages are freed. This is unsuitable for architectures that do not need
2747 * to broadcast an IPI when invalidating TLBs.
2748 *
2749 * Another way to achieve this is to batch up page table containing pages
2750 * belonging to more than one mm_user, then rcu_sched a callback to free those
2751 * pages. Disabling interrupts will allow the gup_fast() walker to both block
2752 * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
2753 * (which is a relatively rare event). The code below adopts this strategy.
2754 *
2755 * Before activating this code, please be aware that the following assumptions
2756 * are currently made:
2757 *
2758 *  *) Either MMU_GATHER_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
2759 *  free pages containing page tables or TLB flushing requires IPI broadcast.
2760 *
2761 *  *) ptes can be read atomically by the architecture.
2762 *
2763 *  *) access_ok is sufficient to validate userspace address ranges.
2764 *
2765 * The last two assumptions can be relaxed by the addition of helper functions.
2766 *
2767 * This code is based heavily on the PowerPC implementation by Nick Piggin.
2768 */
2769#ifdef CONFIG_HAVE_GUP_FAST
2770/*
2771 * Used in the GUP-fast path to determine whether GUP is permitted to work on
2772 * a specific folio.
2773 *
2774 * This call assumes the caller has pinned the folio, that the lowest page table
2775 * level still points to this folio, and that interrupts have been disabled.
2776 *
2777 * GUP-fast must reject all secretmem folios.
2778 *
2779 * Writing to pinned file-backed dirty tracked folios is inherently problematic
2780 * (see comment describing the writable_file_mapping_allowed() function). We
2781 * therefore try to avoid the most egregious case of a long-term mapping doing
2782 * so.
2783 *
2784 * This function cannot be as thorough as that one as the VMA is not available
2785 * in the fast path, so instead we whitelist known good cases and if in doubt,
2786 * fall back to the slow path.
2787 */
2788static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
2789{
2790	bool reject_file_backed = false;
2791	struct address_space *mapping;
2792	bool check_secretmem = false;
2793	unsigned long mapping_flags;
2794
2795	/*
2796	 * If we aren't pinning then no problematic write can occur. A long term
2797	 * pin is the most egregious case so this is the one we disallow.
2798	 */
2799	if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) ==
2800	    (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE))
2801		reject_file_backed = true;
2802
2803	/* We hold a folio reference, so we can safely access folio fields. */
2804
2805	/* secretmem folios are always order-0 folios. */
2806	if (IS_ENABLED(CONFIG_SECRETMEM) && !folio_test_large(folio))
2807		check_secretmem = true;
2808
2809	if (!reject_file_backed && !check_secretmem)
2810		return true;
2811
2812	if (WARN_ON_ONCE(folio_test_slab(folio)))
2813		return false;
2814
2815	/* hugetlb neither requires dirty-tracking nor can be secretmem. */
2816	if (folio_test_hugetlb(folio))
2817		return true;
2818
2819	/*
2820	 * GUP-fast disables IRQs. When IRQS are disabled, RCU grace periods
2821	 * cannot proceed, which means no actions performed under RCU can
2822	 * proceed either.
2823	 *
2824	 * inodes and thus their mappings are freed under RCU, which means the
2825	 * mapping cannot be freed beneath us and thus we can safely dereference
2826	 * it.
2827	 */
2828	lockdep_assert_irqs_disabled();
2829
2830	/*
2831	 * However, there may be operations which _alter_ the mapping, so ensure
2832	 * we read it once and only once.
2833	 */
2834	mapping = READ_ONCE(folio->mapping);
2835
2836	/*
2837	 * The mapping may have been truncated, in any case we cannot determine
2838	 * if this mapping is safe - fall back to slow path to determine how to
2839	 * proceed.
2840	 */
2841	if (!mapping)
2842		return false;
2843
2844	/* Anonymous folios pose no problem. */
2845	mapping_flags = (unsigned long)mapping & PAGE_MAPPING_FLAGS;
2846	if (mapping_flags)
2847		return mapping_flags & PAGE_MAPPING_ANON;
2848
2849	/*
2850	 * At this point, we know the mapping is non-null and points to an
2851	 * address_space object.
2852	 */
2853	if (check_secretmem && secretmem_mapping(mapping))
2854		return false;
2855	/* The only remaining allowed file system is shmem. */
2856	return !reject_file_backed || shmem_mapping(mapping);
2857}
2858
2859static void __maybe_unused gup_fast_undo_dev_pagemap(int *nr, int nr_start,
2860		unsigned int flags, struct page **pages)
2861{
2862	while ((*nr) - nr_start) {
2863		struct folio *folio = page_folio(pages[--(*nr)]);
2864
2865		folio_clear_referenced(folio);
2866		gup_put_folio(folio, 1, flags);
2867	}
2868}
2869
2870#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
2871/*
2872 * GUP-fast relies on pte change detection to avoid concurrent pgtable
2873 * operations.
2874 *
2875 * To pin the page, GUP-fast needs to do below in order:
2876 * (1) pin the page (by prefetching pte), then (2) check pte not changed.
2877 *
2878 * For the rest of pgtable operations where pgtable updates can be racy
2879 * with GUP-fast, we need to do (1) clear pte, then (2) check whether page
2880 * is pinned.
2881 *
2882 * Above will work for all pte-level operations, including THP split.
2883 *
2884 * For THP collapse, it's a bit more complicated because GUP-fast may be
2885 * walking a pgtable page that is being freed (pte is still valid but pmd
2886 * can be cleared already).  To avoid race in such condition, we need to
2887 * also check pmd here to make sure pmd doesn't change (corresponds to
2888 * pmdp_collapse_flush() in the THP collapse code path).
2889 */
2890static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
2891		unsigned long end, unsigned int flags, struct page **pages,
2892		int *nr)
2893{
2894	struct dev_pagemap *pgmap = NULL;
2895	int nr_start = *nr, ret = 0;
2896	pte_t *ptep, *ptem;
2897
2898	ptem = ptep = pte_offset_map(&pmd, addr);
2899	if (!ptep)
2900		return 0;
2901	do {
2902		pte_t pte = ptep_get_lockless(ptep);
2903		struct page *page;
2904		struct folio *folio;
2905
2906		/*
2907		 * Always fallback to ordinary GUP on PROT_NONE-mapped pages:
2908		 * pte_access_permitted() better should reject these pages
2909		 * either way: otherwise, GUP-fast might succeed in
2910		 * cases where ordinary GUP would fail due to VMA access
2911		 * permissions.
2912		 */
2913		if (pte_protnone(pte))
2914			goto pte_unmap;
2915
2916		if (!pte_access_permitted(pte, flags & FOLL_WRITE))
2917			goto pte_unmap;
2918
2919		if (pte_devmap(pte)) {
2920			if (unlikely(flags & FOLL_LONGTERM))
2921				goto pte_unmap;
2922
2923			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
2924			if (unlikely(!pgmap)) {
2925				gup_fast_undo_dev_pagemap(nr, nr_start, flags, pages);
2926				goto pte_unmap;
2927			}
2928		} else if (pte_special(pte))
2929			goto pte_unmap;
2930
2931		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
2932		page = pte_page(pte);
2933
2934		folio = try_grab_folio_fast(page, 1, flags);
2935		if (!folio)
2936			goto pte_unmap;
2937
2938		if (unlikely(pmd_val(pmd) != pmd_val(*pmdp)) ||
2939		    unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) {
2940			gup_put_folio(folio, 1, flags);
2941			goto pte_unmap;
2942		}
2943
2944		if (!gup_fast_folio_allowed(folio, flags)) {
2945			gup_put_folio(folio, 1, flags);
2946			goto pte_unmap;
2947		}
2948
2949		if (!pte_write(pte) && gup_must_unshare(NULL, flags, page)) {
2950			gup_put_folio(folio, 1, flags);
2951			goto pte_unmap;
2952		}
2953
2954		/*
2955		 * We need to make the page accessible if and only if we are
2956		 * going to access its content (the FOLL_PIN case).  Please
2957		 * see Documentation/core-api/pin_user_pages.rst for
2958		 * details.
2959		 */
2960		if (flags & FOLL_PIN) {
2961			ret = arch_make_folio_accessible(folio);
2962			if (ret) {
2963				gup_put_folio(folio, 1, flags);
2964				goto pte_unmap;
2965			}
2966		}
2967		folio_set_referenced(folio);
2968		pages[*nr] = page;
2969		(*nr)++;
2970	} while (ptep++, addr += PAGE_SIZE, addr != end);
2971
2972	ret = 1;
2973
2974pte_unmap:
2975	if (pgmap)
2976		put_dev_pagemap(pgmap);
2977	pte_unmap(ptem);
2978	return ret;
2979}
2980#else
2981
2982/*
2983 * If we can't determine whether or not a pte is special, then fail immediately
2984 * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
2985 * to be special.
2986 *
2987 * For a futex to be placed on a THP tail page, get_futex_key requires a
2988 * get_user_pages_fast_only implementation that can pin pages. Thus it's still
2989 * useful to have gup_fast_pmd_leaf even if we can't operate on ptes.
2990 */
2991static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
2992		unsigned long end, unsigned int flags, struct page **pages,
2993		int *nr)
2994{
2995	return 0;
2996}
2997#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
2998
2999#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
3000static int gup_fast_devmap_leaf(unsigned long pfn, unsigned long addr,
3001	unsigned long end, unsigned int flags, struct page **pages, int *nr)
3002{
3003	int nr_start = *nr;
3004	struct dev_pagemap *pgmap = NULL;
3005
3006	do {
3007		struct folio *folio;
3008		struct page *page = pfn_to_page(pfn);
3009
3010		pgmap = get_dev_pagemap(pfn, pgmap);
3011		if (unlikely(!pgmap)) {
3012			gup_fast_undo_dev_pagemap(nr, nr_start, flags, pages);
3013			break;
3014		}
3015
3016		if (!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)) {
3017			gup_fast_undo_dev_pagemap(nr, nr_start, flags, pages);
3018			break;
3019		}
3020
3021		folio = try_grab_folio_fast(page, 1, flags);
3022		if (!folio) {
3023			gup_fast_undo_dev_pagemap(nr, nr_start, flags, pages);
3024			break;
3025		}
3026		folio_set_referenced(folio);
3027		pages[*nr] = page;
3028		(*nr)++;
3029		pfn++;
3030	} while (addr += PAGE_SIZE, addr != end);
3031
3032	put_dev_pagemap(pgmap);
3033	return addr == end;
3034}
3035
3036static int gup_fast_devmap_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
3037		unsigned long end, unsigned int flags, struct page **pages,
3038		int *nr)
3039{
3040	unsigned long fault_pfn;
3041	int nr_start = *nr;
3042
3043	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
3044	if (!gup_fast_devmap_leaf(fault_pfn, addr, end, flags, pages, nr))
3045		return 0;
3046
3047	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
3048		gup_fast_undo_dev_pagemap(nr, nr_start, flags, pages);
3049		return 0;
3050	}
3051	return 1;
3052}
3053
3054static int gup_fast_devmap_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
3055		unsigned long end, unsigned int flags, struct page **pages,
3056		int *nr)
3057{
3058	unsigned long fault_pfn;
3059	int nr_start = *nr;
3060
3061	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
3062	if (!gup_fast_devmap_leaf(fault_pfn, addr, end, flags, pages, nr))
3063		return 0;
3064
3065	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
3066		gup_fast_undo_dev_pagemap(nr, nr_start, flags, pages);
3067		return 0;
3068	}
3069	return 1;
3070}
3071#else
3072static int gup_fast_devmap_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
3073		unsigned long end, unsigned int flags, struct page **pages,
3074		int *nr)
3075{
3076	BUILD_BUG();
3077	return 0;
3078}
3079
3080static int gup_fast_devmap_pud_leaf(pud_t pud, pud_t *pudp, unsigned long addr,
3081		unsigned long end, unsigned int flags, struct page **pages,
3082		int *nr)
3083{
3084	BUILD_BUG();
3085	return 0;
3086}
3087#endif
3088
3089static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
3090		unsigned long end, unsigned int flags, struct page **pages,
3091		int *nr)
3092{
3093	struct page *page;
3094	struct folio *folio;
3095	int refs;
3096
3097	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
3098		return 0;
3099
3100	if (pmd_special(orig))
3101		return 0;
3102
3103	if (pmd_devmap(orig)) {
3104		if (unlikely(flags & FOLL_LONGTERM))
3105			return 0;
3106		return gup_fast_devmap_pmd_leaf(orig, pmdp, addr, end, flags,
3107					        pages, nr);
3108	}
3109
3110	page = pmd_page(orig);
3111	refs = record_subpages(page, PMD_SIZE, addr, end, pages + *nr);
3112
3113	folio = try_grab_folio_fast(page, refs, flags);
3114	if (!folio)
3115		return 0;
3116
3117	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
3118		gup_put_folio(folio, refs, flags);
3119		return 0;
3120	}
3121
3122	if (!gup_fast_folio_allowed(folio, flags)) {
3123		gup_put_folio(folio, refs, flags);
3124		return 0;
3125	}
3126	if (!pmd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
3127		gup_put_folio(folio, refs, flags);
3128		return 0;
3129	}
3130
3131	*nr += refs;
3132	folio_set_referenced(folio);
3133	return 1;
3134}
3135
3136static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
3137		unsigned long end, unsigned int flags, struct page **pages,
3138		int *nr)
3139{
3140	struct page *page;
3141	struct folio *folio;
3142	int refs;
3143
3144	if (!pud_access_permitted(orig, flags & FOLL_WRITE))
3145		return 0;
3146
3147	if (pud_special(orig))
3148		return 0;
3149
3150	if (pud_devmap(orig)) {
3151		if (unlikely(flags & FOLL_LONGTERM))
3152			return 0;
3153		return gup_fast_devmap_pud_leaf(orig, pudp, addr, end, flags,
3154					        pages, nr);
3155	}
3156
3157	page = pud_page(orig);
3158	refs = record_subpages(page, PUD_SIZE, addr, end, pages + *nr);
3159
3160	folio = try_grab_folio_fast(page, refs, flags);
3161	if (!folio)
3162		return 0;
3163
3164	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
3165		gup_put_folio(folio, refs, flags);
3166		return 0;
3167	}
3168
3169	if (!gup_fast_folio_allowed(folio, flags)) {
3170		gup_put_folio(folio, refs, flags);
3171		return 0;
3172	}
3173
3174	if (!pud_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
3175		gup_put_folio(folio, refs, flags);
3176		return 0;
3177	}
3178
3179	*nr += refs;
3180	folio_set_referenced(folio);
3181	return 1;
3182}
3183
3184static int gup_fast_pgd_leaf(pgd_t orig, pgd_t *pgdp, unsigned long addr,
3185		unsigned long end, unsigned int flags, struct page **pages,
3186		int *nr)
3187{
3188	int refs;
3189	struct page *page;
3190	struct folio *folio;
3191
3192	if (!pgd_access_permitted(orig, flags & FOLL_WRITE))
3193		return 0;
3194
3195	BUILD_BUG_ON(pgd_devmap(orig));
3196
3197	page = pgd_page(orig);
3198	refs = record_subpages(page, PGDIR_SIZE, addr, end, pages + *nr);
3199
3200	folio = try_grab_folio_fast(page, refs, flags);
3201	if (!folio)
3202		return 0;
3203
3204	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
3205		gup_put_folio(folio, refs, flags);
3206		return 0;
3207	}
3208
3209	if (!pgd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
3210		gup_put_folio(folio, refs, flags);
3211		return 0;
3212	}
3213
3214	if (!gup_fast_folio_allowed(folio, flags)) {
3215		gup_put_folio(folio, refs, flags);
3216		return 0;
3217	}
3218
3219	*nr += refs;
3220	folio_set_referenced(folio);
3221	return 1;
3222}
3223
3224static int gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
3225		unsigned long end, unsigned int flags, struct page **pages,
3226		int *nr)
3227{
3228	unsigned long next;
3229	pmd_t *pmdp;
3230
3231	pmdp = pmd_offset_lockless(pudp, pud, addr);
3232	do {
3233		pmd_t pmd = pmdp_get_lockless(pmdp);
3234
3235		next = pmd_addr_end(addr, end);
3236		if (!pmd_present(pmd))
3237			return 0;
3238
3239		if (unlikely(pmd_leaf(pmd))) {
3240			/* See gup_fast_pte_range() */
3241			if (pmd_protnone(pmd))
3242				return 0;
3243
3244			if (!gup_fast_pmd_leaf(pmd, pmdp, addr, next, flags,
3245				pages, nr))
3246				return 0;
3247
3248		} else if (!gup_fast_pte_range(pmd, pmdp, addr, next, flags,
3249					       pages, nr))
3250			return 0;
3251	} while (pmdp++, addr = next, addr != end);
3252
3253	return 1;
3254}
3255
3256static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr,
3257		unsigned long end, unsigned int flags, struct page **pages,
3258		int *nr)
3259{
3260	unsigned long next;
3261	pud_t *pudp;
3262
3263	pudp = pud_offset_lockless(p4dp, p4d, addr);
3264	do {
3265		pud_t pud = READ_ONCE(*pudp);
3266
3267		next = pud_addr_end(addr, end);
3268		if (unlikely(!pud_present(pud)))
3269			return 0;
3270		if (unlikely(pud_leaf(pud))) {
3271			if (!gup_fast_pud_leaf(pud, pudp, addr, next, flags,
3272					       pages, nr))
3273				return 0;
3274		} else if (!gup_fast_pmd_range(pudp, pud, addr, next, flags,
3275					       pages, nr))
3276			return 0;
3277	} while (pudp++, addr = next, addr != end);
3278
3279	return 1;
3280}
3281
3282static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
3283		unsigned long end, unsigned int flags, struct page **pages,
3284		int *nr)
3285{
3286	unsigned long next;
3287	p4d_t *p4dp;
3288
3289	p4dp = p4d_offset_lockless(pgdp, pgd, addr);
3290	do {
3291		p4d_t p4d = READ_ONCE(*p4dp);
3292
3293		next = p4d_addr_end(addr, end);
3294		if (!p4d_present(p4d))
3295			return 0;
3296		BUILD_BUG_ON(p4d_leaf(p4d));
3297		if (!gup_fast_pud_range(p4dp, p4d, addr, next, flags,
3298					pages, nr))
3299			return 0;
3300	} while (p4dp++, addr = next, addr != end);
3301
3302	return 1;
3303}
3304
3305static void gup_fast_pgd_range(unsigned long addr, unsigned long end,
3306		unsigned int flags, struct page **pages, int *nr)
3307{
3308	unsigned long next;
3309	pgd_t *pgdp;
3310
3311	pgdp = pgd_offset(current->mm, addr);
3312	do {
3313		pgd_t pgd = READ_ONCE(*pgdp);
3314
3315		next = pgd_addr_end(addr, end);
3316		if (pgd_none(pgd))
3317			return;
3318		if (unlikely(pgd_leaf(pgd))) {
3319			if (!gup_fast_pgd_leaf(pgd, pgdp, addr, next, flags,
3320					       pages, nr))
3321				return;
3322		} else if (!gup_fast_p4d_range(pgdp, pgd, addr, next, flags,
3323					       pages, nr))
3324			return;
3325	} while (pgdp++, addr = next, addr != end);
3326}
3327#else
3328static inline void gup_fast_pgd_range(unsigned long addr, unsigned long end,
3329		unsigned int flags, struct page **pages, int *nr)
3330{
3331}
3332#endif /* CONFIG_HAVE_GUP_FAST */
3333
3334#ifndef gup_fast_permitted
3335/*
3336 * Check if it's allowed to use get_user_pages_fast_only() for the range, or
3337 * we need to fall back to the slow version:
3338 */
3339static bool gup_fast_permitted(unsigned long start, unsigned long end)
3340{
3341	return true;
3342}
3343#endif
3344
3345static unsigned long gup_fast(unsigned long start, unsigned long end,
3346		unsigned int gup_flags, struct page **pages)
3347{
3348	unsigned long flags;
3349	int nr_pinned = 0;
3350	unsigned seq;
3351
3352	if (!IS_ENABLED(CONFIG_HAVE_GUP_FAST) ||
3353	    !gup_fast_permitted(start, end))
3354		return 0;
3355
3356	if (gup_flags & FOLL_PIN) {
3357		seq = raw_read_seqcount(&current->mm->write_protect_seq);
3358		if (seq & 1)
3359			return 0;
3360	}
3361
3362	/*
3363	 * Disable interrupts. The nested form is used, in order to allow full,
3364	 * general purpose use of this routine.
3365	 *
3366	 * With interrupts disabled, we block page table pages from being freed
3367	 * from under us. See struct mmu_table_batch comments in
3368	 * include/asm-generic/tlb.h for more details.
3369	 *
3370	 * We do not adopt an rcu_read_lock() here as we also want to block IPIs
3371	 * that come from THPs splitting.
3372	 */
3373	local_irq_save(flags);
3374	gup_fast_pgd_range(start, end, gup_flags, pages, &nr_pinned);
3375	local_irq_restore(flags);
3376
3377	/*
3378	 * When pinning pages for DMA there could be a concurrent write protect
3379	 * from fork() via copy_page_range(), in this case always fail GUP-fast.
3380	 */
3381	if (gup_flags & FOLL_PIN) {
3382		if (read_seqcount_retry(&current->mm->write_protect_seq, seq)) {
3383			gup_fast_unpin_user_pages(pages, nr_pinned);
3384			return 0;
3385		} else {
3386			sanity_check_pinned_pages(pages, nr_pinned);
3387		}
3388	}
3389	return nr_pinned;
3390}
3391
3392static int gup_fast_fallback(unsigned long start, unsigned long nr_pages,
3393		unsigned int gup_flags, struct page **pages)
3394{
3395	unsigned long len, end;
3396	unsigned long nr_pinned;
3397	int locked = 0;
3398	int ret;
3399
3400	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
3401				       FOLL_FORCE | FOLL_PIN | FOLL_GET |
3402				       FOLL_FAST_ONLY | FOLL_NOFAULT |
3403				       FOLL_PCI_P2PDMA | FOLL_HONOR_NUMA_FAULT)))
3404		return -EINVAL;
3405
3406	if (gup_flags & FOLL_PIN)
3407		mm_set_has_pinned_flag(&current->mm->flags);
3408
3409	if (!(gup_flags & FOLL_FAST_ONLY))
3410		might_lock_read(&current->mm->mmap_lock);
3411
3412	start = untagged_addr(start) & PAGE_MASK;
3413	len = nr_pages << PAGE_SHIFT;
3414	if (check_add_overflow(start, len, &end))
3415		return -EOVERFLOW;
3416	if (end > TASK_SIZE_MAX)
3417		return -EFAULT;
3418	if (unlikely(!access_ok((void __user *)start, len)))
3419		return -EFAULT;
3420
3421	nr_pinned = gup_fast(start, end, gup_flags, pages);
3422	if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
3423		return nr_pinned;
3424
3425	/* Slow path: try to get the remaining pages with get_user_pages */
3426	start += nr_pinned << PAGE_SHIFT;
3427	pages += nr_pinned;
3428	ret = __gup_longterm_locked(current->mm, start, nr_pages - nr_pinned,
3429				    pages, &locked,
3430				    gup_flags | FOLL_TOUCH | FOLL_UNLOCKABLE);
3431	if (ret < 0) {
3432		/*
3433		 * The caller has to unpin the pages we already pinned so
3434		 * returning -errno is not an option
3435		 */
3436		if (nr_pinned)
3437			return nr_pinned;
3438		return ret;
3439	}
3440	return ret + nr_pinned;
3441}
3442
3443/**
3444 * get_user_pages_fast_only() - pin user pages in memory
3445 * @start:      starting user address
3446 * @nr_pages:   number of pages from start to pin
3447 * @gup_flags:  flags modifying pin behaviour
3448 * @pages:      array that receives pointers to the pages pinned.
3449 *              Should be at least nr_pages long.
3450 *
3451 * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
3452 * the regular GUP.
3453 *
3454 * If the architecture does not support this function, simply return with no
3455 * pages pinned.
3456 *
3457 * Careful, careful! COW breaking can go either way, so a non-write
3458 * access can get ambiguous page results. If you call this function without
3459 * 'write' set, you'd better be sure that you're ok with that ambiguity.
3460 */
3461int get_user_pages_fast_only(unsigned long start, int nr_pages,
3462			     unsigned int gup_flags, struct page **pages)
3463{
3464	/*
3465	 * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
3466	 * because gup fast is always a "pin with a +1 page refcount" request.
3467	 *
3468	 * FOLL_FAST_ONLY is required in order to match the API description of
3469	 * this routine: no fall back to regular ("slow") GUP.
3470	 */
3471	if (!is_valid_gup_args(pages, NULL, &gup_flags,
3472			       FOLL_GET | FOLL_FAST_ONLY))
3473		return -EINVAL;
3474
3475	return gup_fast_fallback(start, nr_pages, gup_flags, pages);
3476}
3477EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
3478
3479/**
3480 * get_user_pages_fast() - pin user pages in memory
3481 * @start:      starting user address
3482 * @nr_pages:   number of pages from start to pin
3483 * @gup_flags:  flags modifying pin behaviour
3484 * @pages:      array that receives pointers to the pages pinned.
3485 *              Should be at least nr_pages long.
3486 *
3487 * Attempt to pin user pages in memory without taking mm->mmap_lock.
3488 * If not successful, it will fall back to taking the lock and
3489 * calling get_user_pages().
3490 *
3491 * Returns number of pages pinned. This may be fewer than the number requested.
3492 * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
3493 * -errno.
3494 */
3495int get_user_pages_fast(unsigned long start, int nr_pages,
3496			unsigned int gup_flags, struct page **pages)
3497{
3498	/*
3499	 * The caller may or may not have explicitly set FOLL_GET; either way is
3500	 * OK. However, internally (within mm/gup.c), gup fast variants must set
3501	 * FOLL_GET, because gup fast is always a "pin with a +1 page refcount"
3502	 * request.
3503	 */
3504	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_GET))
3505		return -EINVAL;
3506	return gup_fast_fallback(start, nr_pages, gup_flags, pages);
3507}
3508EXPORT_SYMBOL_GPL(get_user_pages_fast);
3509
3510/**
3511 * pin_user_pages_fast() - pin user pages in memory without taking locks
3512 *
3513 * @start:      starting user address
3514 * @nr_pages:   number of pages from start to pin
3515 * @gup_flags:  flags modifying pin behaviour
3516 * @pages:      array that receives pointers to the pages pinned.
3517 *              Should be at least nr_pages long.
3518 *
3519 * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
3520 * get_user_pages_fast() for documentation on the function arguments, because
3521 * the arguments here are identical.
3522 *
3523 * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
3524 * see Documentation/core-api/pin_user_pages.rst for further details.
3525 *
3526 * Note that if a zero_page is amongst the returned pages, it will not have
3527 * pins in it and unpin_user_page() will not remove pins from it.
3528 */
3529int pin_user_pages_fast(unsigned long start, int nr_pages,
3530			unsigned int gup_flags, struct page **pages)
3531{
3532	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_PIN))
3533		return -EINVAL;
3534	return gup_fast_fallback(start, nr_pages, gup_flags, pages);
3535}
3536EXPORT_SYMBOL_GPL(pin_user_pages_fast);
3537
3538/**
3539 * pin_user_pages_remote() - pin pages of a remote process
3540 *
3541 * @mm:		mm_struct of target mm
3542 * @start:	starting user address
3543 * @nr_pages:	number of pages from start to pin
3544 * @gup_flags:	flags modifying lookup behaviour
3545 * @pages:	array that receives pointers to the pages pinned.
3546 *		Should be at least nr_pages long.
3547 * @locked:	pointer to lock flag indicating whether lock is held and
3548 *		subsequently whether VM_FAULT_RETRY functionality can be
3549 *		utilised. Lock must initially be held.
3550 *
3551 * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See
3552 * get_user_pages_remote() for documentation on the function arguments, because
3553 * the arguments here are identical.
3554 *
3555 * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
3556 * see Documentation/core-api/pin_user_pages.rst for details.
3557 *
3558 * Note that if a zero_page is amongst the returned pages, it will not have
3559 * pins in it and unpin_user_page*() will not remove pins from it.
3560 */
3561long pin_user_pages_remote(struct mm_struct *mm,
3562			   unsigned long start, unsigned long nr_pages,
3563			   unsigned int gup_flags, struct page **pages,
3564			   int *locked)
3565{
3566	int local_locked = 1;
3567
3568	if (!is_valid_gup_args(pages, locked, &gup_flags,
3569			       FOLL_PIN | FOLL_TOUCH | FOLL_REMOTE))
3570		return 0;
3571	return __gup_longterm_locked(mm, start, nr_pages, pages,
3572				     locked ? locked : &local_locked,
3573				     gup_flags);
3574}
3575EXPORT_SYMBOL(pin_user_pages_remote);
3576
3577/**
3578 * pin_user_pages() - pin user pages in memory for use by other devices
3579 *
3580 * @start:	starting user address
3581 * @nr_pages:	number of pages from start to pin
3582 * @gup_flags:	flags modifying lookup behaviour
3583 * @pages:	array that receives pointers to the pages pinned.
3584 *		Should be at least nr_pages long.
3585 *
3586 * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and
3587 * FOLL_PIN is set.
3588 *
3589 * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
3590 * see Documentation/core-api/pin_user_pages.rst for details.
3591 *
3592 * Note that if a zero_page is amongst the returned pages, it will not have
3593 * pins in it and unpin_user_page*() will not remove pins from it.
3594 */
3595long pin_user_pages(unsigned long start, unsigned long nr_pages,
3596		    unsigned int gup_flags, struct page **pages)
3597{
3598	int locked = 1;
3599
3600	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_PIN))
3601		return 0;
3602	return __gup_longterm_locked(current->mm, start, nr_pages,
3603				     pages, &locked, gup_flags);
3604}
3605EXPORT_SYMBOL(pin_user_pages);
3606
3607/*
3608 * pin_user_pages_unlocked() is the FOLL_PIN variant of
3609 * get_user_pages_unlocked(). Behavior is the same, except that this one sets
3610 * FOLL_PIN and rejects FOLL_GET.
3611 *
3612 * Note that if a zero_page is amongst the returned pages, it will not have
3613 * pins in it and unpin_user_page*() will not remove pins from it.
3614 */
3615long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
3616			     struct page **pages, unsigned int gup_flags)
3617{
3618	int locked = 0;
3619
3620	if (!is_valid_gup_args(pages, NULL, &gup_flags,
3621			       FOLL_PIN | FOLL_TOUCH | FOLL_UNLOCKABLE))
3622		return 0;
3623
3624	return __gup_longterm_locked(current->mm, start, nr_pages, pages,
3625				     &locked, gup_flags);
3626}
3627EXPORT_SYMBOL(pin_user_pages_unlocked);
3628
3629/**
3630 * memfd_pin_folios() - pin folios associated with a memfd
3631 * @memfd:      the memfd whose folios are to be pinned
3632 * @start:      the first memfd offset
3633 * @end:        the last memfd offset (inclusive)
3634 * @folios:     array that receives pointers to the folios pinned
3635 * @max_folios: maximum number of entries in @folios
3636 * @offset:     the offset into the first folio
3637 *
3638 * Attempt to pin folios associated with a memfd in the contiguous range
3639 * [start, end]. Given that a memfd is either backed by shmem or hugetlb,
3640 * the folios can either be found in the page cache or need to be allocated
3641 * if necessary. Once the folios are located, they are all pinned via
3642 * FOLL_PIN and @offset is populatedwith the offset into the first folio.
3643 * And, eventually, these pinned folios must be released either using
3644 * unpin_folios() or unpin_folio().
3645 *
3646 * It must be noted that the folios may be pinned for an indefinite amount
3647 * of time. And, in most cases, the duration of time they may stay pinned
3648 * would be controlled by the userspace. This behavior is effectively the
3649 * same as using FOLL_LONGTERM with other GUP APIs.
3650 *
3651 * Returns number of folios pinned, which could be less than @max_folios
3652 * as it depends on the folio sizes that cover the range [start, end].
3653 * If no folios were pinned, it returns -errno.
3654 */
3655long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
3656		      struct folio **folios, unsigned int max_folios,
3657		      pgoff_t *offset)
3658{
3659	unsigned int flags, nr_folios, nr_found;
3660	unsigned int i, pgshift = PAGE_SHIFT;
3661	pgoff_t start_idx, end_idx, next_idx;
3662	struct folio *folio = NULL;
3663	struct folio_batch fbatch;
3664	struct hstate *h;
3665	long ret = -EINVAL;
3666
3667	if (start < 0 || start > end || !max_folios)
3668		return -EINVAL;
3669
3670	if (!memfd)
3671		return -EINVAL;
3672
3673	if (!shmem_file(memfd) && !is_file_hugepages(memfd))
3674		return -EINVAL;
3675
3676	if (end >= i_size_read(file_inode(memfd)))
3677		return -EINVAL;
3678
3679	if (is_file_hugepages(memfd)) {
3680		h = hstate_file(memfd);
3681		pgshift = huge_page_shift(h);
3682	}
3683
3684	flags = memalloc_pin_save();
3685	do {
3686		nr_folios = 0;
3687		start_idx = start >> pgshift;
3688		end_idx = end >> pgshift;
3689		if (is_file_hugepages(memfd)) {
3690			start_idx <<= huge_page_order(h);
3691			end_idx <<= huge_page_order(h);
3692		}
3693
3694		folio_batch_init(&fbatch);
3695		while (start_idx <= end_idx && nr_folios < max_folios) {
3696			/*
3697			 * In most cases, we should be able to find the folios
3698			 * in the page cache. If we cannot find them for some
3699			 * reason, we try to allocate them and add them to the
3700			 * page cache.
3701			 */
3702			nr_found = filemap_get_folios_contig(memfd->f_mapping,
3703							     &start_idx,
3704							     end_idx,
3705							     &fbatch);
3706			if (folio) {
3707				folio_put(folio);
3708				folio = NULL;
3709			}
3710
3711			next_idx = 0;
3712			for (i = 0; i < nr_found; i++) {
3713				/*
3714				 * As there can be multiple entries for a
3715				 * given folio in the batch returned by
3716				 * filemap_get_folios_contig(), the below
3717				 * check is to ensure that we pin and return a
3718				 * unique set of folios between start and end.
3719				 */
3720				if (next_idx &&
3721				    next_idx != folio_index(fbatch.folios[i]))
3722					continue;
3723
3724				folio = page_folio(&fbatch.folios[i]->page);
3725
3726				if (try_grab_folio(folio, 1, FOLL_PIN)) {
3727					folio_batch_release(&fbatch);
3728					ret = -EINVAL;
3729					goto err;
3730				}
3731
3732				if (nr_folios == 0)
3733					*offset = offset_in_folio(folio, start);
3734
3735				folios[nr_folios] = folio;
3736				next_idx = folio_next_index(folio);
3737				if (++nr_folios == max_folios)
3738					break;
3739			}
3740
3741			folio = NULL;
3742			folio_batch_release(&fbatch);
3743			if (!nr_found) {
3744				folio = memfd_alloc_folio(memfd, start_idx);
3745				if (IS_ERR(folio)) {
3746					ret = PTR_ERR(folio);
3747					if (ret != -EEXIST)
3748						goto err;
3749					folio = NULL;
3750				}
3751			}
3752		}
3753
3754		ret = check_and_migrate_movable_folios(nr_folios, folios);
3755	} while (ret == -EAGAIN);
3756
3757	memalloc_pin_restore(flags);
3758	return ret ? ret : nr_folios;
3759err:
3760	memalloc_pin_restore(flags);
3761	unpin_folios(folios, nr_folios);
3762
3763	return ret;
3764}
3765EXPORT_SYMBOL_GPL(memfd_pin_folios);
3766
3767/**
3768 * folio_add_pins() - add pins to an already-pinned folio
3769 * @folio: the folio to add more pins to
3770 * @pins: number of pins to add
3771 *
3772 * Try to add more pins to an already-pinned folio. The semantics
3773 * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot
3774 * be changed.
3775 *
3776 * This function is helpful when having obtained a pin on a large folio
3777 * using memfd_pin_folios(), but wanting to logically unpin parts
3778 * (e.g., individual pages) of the folio later, for example, using
3779 * unpin_user_page_range_dirty_lock().
3780 *
3781 * This is not the right interface to initially pin a folio.
3782 */
3783int folio_add_pins(struct folio *folio, unsigned int pins)
3784{
3785	VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio));
3786
3787	return try_grab_folio(folio, pins, FOLL_PIN);
3788}
3789EXPORT_SYMBOL_GPL(folio_add_pins);