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/memremap.h>
   9#include <linux/pagemap.h>
  10#include <linux/rmap.h>
  11#include <linux/swap.h>
  12#include <linux/swapops.h>
  13
  14#include <linux/sched/signal.h>
  15#include <linux/rwsem.h>
  16#include <linux/hugetlb.h>
  17#include <linux/migrate.h>
  18#include <linux/mm_inline.h>
  19#include <linux/sched/mm.h>
  20
  21#include <asm/mmu_context.h>
  22#include <asm/tlbflush.h>
  23
  24#include "internal.h"
  25
  26struct follow_page_context {
  27	struct dev_pagemap *pgmap;
  28	unsigned int page_mask;
  29};
  30
  31static void hpage_pincount_add(struct page *page, int refs)
  32{
  33	VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
  34	VM_BUG_ON_PAGE(page != compound_head(page), page);
  35
  36	atomic_add(refs, compound_pincount_ptr(page));
  37}
  38
  39static void hpage_pincount_sub(struct page *page, int refs)
  40{
  41	VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
  42	VM_BUG_ON_PAGE(page != compound_head(page), page);
  43
  44	atomic_sub(refs, compound_pincount_ptr(page));
  45}
  46
  47/*
  48 * Return the compound head page with ref appropriately incremented,
  49 * or NULL if that failed.
  50 */
  51static inline struct page *try_get_compound_head(struct page *page, int refs)
  52{
  53	struct page *head = compound_head(page);
  54
  55	if (WARN_ON_ONCE(page_ref_count(head) < 0))
  56		return NULL;
  57	if (unlikely(!page_cache_add_speculative(head, refs)))
  58		return NULL;
  59	return head;
  60}
  61
  62/*
  63 * try_grab_compound_head() - attempt to elevate a page's refcount, by a
  64 * flags-dependent amount.
  65 *
  66 * "grab" names in this file mean, "look at flags to decide whether to use
  67 * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
  68 *
  69 * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the
  70 * same time. (That's true throughout the get_user_pages*() and
  71 * pin_user_pages*() APIs.) Cases:
  72 *
  73 *    FOLL_GET: page's refcount will be incremented by 1.
  74 *    FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.
  75 *
  76 * Return: head page (with refcount appropriately incremented) for success, or
  77 * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's
  78 * considered failure, and furthermore, a likely bug in the caller, so a warning
  79 * is also emitted.
  80 */
  81static __maybe_unused struct page *try_grab_compound_head(struct page *page,
  82							  int refs,
  83							  unsigned int flags)
  84{
  85	if (flags & FOLL_GET)
  86		return try_get_compound_head(page, refs);
  87	else if (flags & FOLL_PIN) {
  88		int orig_refs = refs;
  89
  90		/*
  91		 * Can't do FOLL_LONGTERM + FOLL_PIN with CMA in the gup fast
  92		 * path, so fail and let the caller fall back to the slow path.
  93		 */
  94		if (unlikely(flags & FOLL_LONGTERM) &&
  95				is_migrate_cma_page(page))
  96			return NULL;
  97
  98		/*
  99		 * When pinning a compound page of order > 1 (which is what
 100		 * hpage_pincount_available() checks for), use an exact count to
 101		 * track it, via hpage_pincount_add/_sub().
 102		 *
 103		 * However, be sure to *also* increment the normal page refcount
 104		 * field at least once, so that the page really is pinned.
 105		 */
 106		if (!hpage_pincount_available(page))
 107			refs *= GUP_PIN_COUNTING_BIAS;
 108
 109		page = try_get_compound_head(page, refs);
 110		if (!page)
 111			return NULL;
 112
 113		if (hpage_pincount_available(page))
 114			hpage_pincount_add(page, refs);
 115
 116		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED,
 117				    orig_refs);
 118
 119		return page;
 120	}
 121
 122	WARN_ON_ONCE(1);
 123	return NULL;
 124}
 125
 126/**
 127 * try_grab_page() - elevate a page's refcount by a flag-dependent amount
 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 page's refcount.
 133 *
 134 * @page:    pointer to page to be grabbed
 135 * @flags:   gup flags: these are the FOLL_* flag values.
 136 *
 137 * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
 138 * time. Cases:
 139 *
 140 *    FOLL_GET: page's refcount will be incremented by 1.
 141 *    FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.
 142 *
 143 * Return: true for success, or if no action was required (if neither FOLL_PIN
 144 * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or
 145 * FOLL_PIN was set, but the page could not be grabbed.
 146 */
 147bool __must_check try_grab_page(struct page *page, unsigned int flags)
 148{
 149	WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN));
 150
 151	if (flags & FOLL_GET)
 152		return try_get_page(page);
 153	else if (flags & FOLL_PIN) {
 154		int refs = 1;
 155
 156		page = compound_head(page);
 157
 158		if (WARN_ON_ONCE(page_ref_count(page) <= 0))
 159			return false;
 160
 161		if (hpage_pincount_available(page))
 162			hpage_pincount_add(page, 1);
 163		else
 164			refs = GUP_PIN_COUNTING_BIAS;
 165
 166		/*
 167		 * Similar to try_grab_compound_head(): even if using the
 168		 * hpage_pincount_add/_sub() routines, be sure to
 169		 * *also* increment the normal page refcount field at least
 170		 * once, so that the page really is pinned.
 171		 */
 172		page_ref_add(page, refs);
 173
 174		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
 175	}
 176
 177	return true;
 178}
 179
 180#ifdef CONFIG_DEV_PAGEMAP_OPS
 181static bool __unpin_devmap_managed_user_page(struct page *page)
 182{
 183	int count, refs = 1;
 184
 185	if (!page_is_devmap_managed(page))
 186		return false;
 187
 188	if (hpage_pincount_available(page))
 189		hpage_pincount_sub(page, 1);
 190	else
 191		refs = GUP_PIN_COUNTING_BIAS;
 192
 193	count = page_ref_sub_return(page, refs);
 194
 195	mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
 196	/*
 197	 * devmap page refcounts are 1-based, rather than 0-based: if
 198	 * refcount is 1, then the page is free and the refcount is
 199	 * stable because nobody holds a reference on the page.
 200	 */
 201	if (count == 1)
 202		free_devmap_managed_page(page);
 203	else if (!count)
 204		__put_page(page);
 205
 206	return true;
 207}
 208#else
 209static bool __unpin_devmap_managed_user_page(struct page *page)
 210{
 211	return false;
 212}
 213#endif /* CONFIG_DEV_PAGEMAP_OPS */
 214
 215/**
 216 * unpin_user_page() - release a dma-pinned page
 217 * @page:            pointer to page to be released
 218 *
 219 * Pages that were pinned via pin_user_pages*() must be released via either
 220 * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so
 221 * that such pages can be separately tracked and uniquely handled. In
 222 * particular, interactions with RDMA and filesystems need special handling.
 223 */
 224void unpin_user_page(struct page *page)
 225{
 226	int refs = 1;
 227
 228	page = compound_head(page);
 229
 230	/*
 231	 * For devmap managed pages we need to catch refcount transition from
 232	 * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
 233	 * page is free and we need to inform the device driver through
 234	 * callback. See include/linux/memremap.h and HMM for details.
 235	 */
 236	if (__unpin_devmap_managed_user_page(page))
 237		return;
 238
 239	if (hpage_pincount_available(page))
 240		hpage_pincount_sub(page, 1);
 241	else
 242		refs = GUP_PIN_COUNTING_BIAS;
 243
 244	if (page_ref_sub_and_test(page, refs))
 245		__put_page(page);
 246
 247	mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
 248}
 249EXPORT_SYMBOL(unpin_user_page);
 250
 251/**
 252 * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
 253 * @pages:  array of pages to be maybe marked dirty, and definitely released.
 254 * @npages: number of pages in the @pages array.
 255 * @make_dirty: whether to mark the pages dirty
 256 *
 257 * "gup-pinned page" refers to a page that has had one of the get_user_pages()
 258 * variants called on that page.
 259 *
 260 * For each page in the @pages array, make that page (or its head page, if a
 261 * compound page) dirty, if @make_dirty is true, and if the page was previously
 262 * listed as clean. In any case, releases all pages using unpin_user_page(),
 263 * possibly via unpin_user_pages(), for the non-dirty case.
 264 *
 265 * Please see the unpin_user_page() documentation for details.
 266 *
 267 * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
 268 * required, then the caller should a) verify that this is really correct,
 269 * because _lock() is usually required, and b) hand code it:
 270 * set_page_dirty_lock(), unpin_user_page().
 271 *
 272 */
 273void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 274				 bool make_dirty)
 275{
 276	unsigned long index;
 277
 278	/*
 279	 * TODO: this can be optimized for huge pages: if a series of pages is
 280	 * physically contiguous and part of the same compound page, then a
 281	 * single operation to the head page should suffice.
 282	 */
 283
 284	if (!make_dirty) {
 285		unpin_user_pages(pages, npages);
 286		return;
 287	}
 288
 289	for (index = 0; index < npages; index++) {
 290		struct page *page = compound_head(pages[index]);
 291		/*
 292		 * Checking PageDirty at this point may race with
 293		 * clear_page_dirty_for_io(), but that's OK. Two key
 294		 * cases:
 295		 *
 296		 * 1) This code sees the page as already dirty, so it
 297		 * skips the call to set_page_dirty(). That could happen
 298		 * because clear_page_dirty_for_io() called
 299		 * page_mkclean(), followed by set_page_dirty().
 300		 * However, now the page is going to get written back,
 301		 * which meets the original intention of setting it
 302		 * dirty, so all is well: clear_page_dirty_for_io() goes
 303		 * on to call TestClearPageDirty(), and write the page
 304		 * back.
 305		 *
 306		 * 2) This code sees the page as clean, so it calls
 307		 * set_page_dirty(). The page stays dirty, despite being
 308		 * written back, so it gets written back again in the
 309		 * next writeback cycle. This is harmless.
 310		 */
 311		if (!PageDirty(page))
 312			set_page_dirty_lock(page);
 313		unpin_user_page(page);
 314	}
 315}
 316EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
 317
 318/**
 319 * unpin_user_pages() - release an array of gup-pinned pages.
 320 * @pages:  array of pages to be marked dirty and released.
 321 * @npages: number of pages in the @pages array.
 322 *
 323 * For each page in the @pages array, release the page using unpin_user_page().
 324 *
 325 * Please see the unpin_user_page() documentation for details.
 326 */
 327void unpin_user_pages(struct page **pages, unsigned long npages)
 328{
 329	unsigned long index;
 330
 331	/*
 332	 * TODO: this can be optimized for huge pages: if a series of pages is
 333	 * physically contiguous and part of the same compound page, then a
 334	 * single operation to the head page should suffice.
 335	 */
 336	for (index = 0; index < npages; index++)
 337		unpin_user_page(pages[index]);
 338}
 339EXPORT_SYMBOL(unpin_user_pages);
 340
 341#ifdef CONFIG_MMU
 342static struct page *no_page_table(struct vm_area_struct *vma,
 343		unsigned int flags)
 344{
 345	/*
 346	 * When core dumping an enormous anonymous area that nobody
 347	 * has touched so far, we don't want to allocate unnecessary pages or
 348	 * page tables.  Return error instead of NULL to skip handle_mm_fault,
 349	 * then get_dump_page() will return NULL to leave a hole in the dump.
 350	 * But we can only make this optimization where a hole would surely
 351	 * be zero-filled if handle_mm_fault() actually did handle it.
 352	 */
 353	if ((flags & FOLL_DUMP) &&
 354			(vma_is_anonymous(vma) || !vma->vm_ops->fault))
 355		return ERR_PTR(-EFAULT);
 356	return NULL;
 357}
 358
 359static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
 360		pte_t *pte, unsigned int flags)
 361{
 362	/* No page to get reference */
 363	if (flags & FOLL_GET)
 364		return -EFAULT;
 365
 366	if (flags & FOLL_TOUCH) {
 367		pte_t entry = *pte;
 368
 369		if (flags & FOLL_WRITE)
 370			entry = pte_mkdirty(entry);
 371		entry = pte_mkyoung(entry);
 372
 373		if (!pte_same(*pte, entry)) {
 374			set_pte_at(vma->vm_mm, address, pte, entry);
 375			update_mmu_cache(vma, address, pte);
 376		}
 377	}
 378
 379	/* Proper page table entry exists, but no corresponding struct page */
 380	return -EEXIST;
 381}
 382
 383/*
 384 * FOLL_FORCE can write to even unwritable pte's, but only
 385 * after we've gone through a COW cycle and they are dirty.
 386 */
 387static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
 388{
 389	return pte_write(pte) ||
 390		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
 391}
 392
 393static struct page *follow_page_pte(struct vm_area_struct *vma,
 394		unsigned long address, pmd_t *pmd, unsigned int flags,
 395		struct dev_pagemap **pgmap)
 396{
 397	struct mm_struct *mm = vma->vm_mm;
 398	struct page *page;
 399	spinlock_t *ptl;
 400	pte_t *ptep, pte;
 401	int ret;
 402
 403	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
 404	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
 405			 (FOLL_PIN | FOLL_GET)))
 406		return ERR_PTR(-EINVAL);
 407retry:
 408	if (unlikely(pmd_bad(*pmd)))
 409		return no_page_table(vma, flags);
 410
 411	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 412	pte = *ptep;
 413	if (!pte_present(pte)) {
 414		swp_entry_t entry;
 415		/*
 416		 * KSM's break_ksm() relies upon recognizing a ksm page
 417		 * even while it is being migrated, so for that case we
 418		 * need migration_entry_wait().
 419		 */
 420		if (likely(!(flags & FOLL_MIGRATION)))
 421			goto no_page;
 422		if (pte_none(pte))
 423			goto no_page;
 424		entry = pte_to_swp_entry(pte);
 425		if (!is_migration_entry(entry))
 426			goto no_page;
 427		pte_unmap_unlock(ptep, ptl);
 428		migration_entry_wait(mm, pmd, address);
 429		goto retry;
 430	}
 431	if ((flags & FOLL_NUMA) && pte_protnone(pte))
 432		goto no_page;
 433	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
 434		pte_unmap_unlock(ptep, ptl);
 435		return NULL;
 436	}
 437
 438	page = vm_normal_page(vma, address, pte);
 439	if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
 440		/*
 441		 * Only return device mapping pages in the FOLL_GET or FOLL_PIN
 442		 * case since they are only valid while holding the pgmap
 443		 * reference.
 444		 */
 445		*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
 446		if (*pgmap)
 447			page = pte_page(pte);
 448		else
 449			goto no_page;
 450	} else if (unlikely(!page)) {
 451		if (flags & FOLL_DUMP) {
 452			/* Avoid special (like zero) pages in core dumps */
 453			page = ERR_PTR(-EFAULT);
 454			goto out;
 455		}
 456
 457		if (is_zero_pfn(pte_pfn(pte))) {
 458			page = pte_page(pte);
 459		} else {
 460			ret = follow_pfn_pte(vma, address, ptep, flags);
 461			page = ERR_PTR(ret);
 462			goto out;
 463		}
 464	}
 465
 466	if (flags & FOLL_SPLIT && PageTransCompound(page)) {
 467		get_page(page);
 468		pte_unmap_unlock(ptep, ptl);
 469		lock_page(page);
 470		ret = split_huge_page(page);
 471		unlock_page(page);
 472		put_page(page);
 473		if (ret)
 474			return ERR_PTR(ret);
 475		goto retry;
 476	}
 477
 478	/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
 479	if (unlikely(!try_grab_page(page, flags))) {
 480		page = ERR_PTR(-ENOMEM);
 481		goto out;
 482	}
 483	/*
 484	 * We need to make the page accessible if and only if we are going
 485	 * to access its content (the FOLL_PIN case).  Please see
 486	 * Documentation/core-api/pin_user_pages.rst for details.
 487	 */
 488	if (flags & FOLL_PIN) {
 489		ret = arch_make_page_accessible(page);
 490		if (ret) {
 491			unpin_user_page(page);
 492			page = ERR_PTR(ret);
 493			goto out;
 494		}
 495	}
 496	if (flags & FOLL_TOUCH) {
 497		if ((flags & FOLL_WRITE) &&
 498		    !pte_dirty(pte) && !PageDirty(page))
 499			set_page_dirty(page);
 500		/*
 501		 * pte_mkyoung() would be more correct here, but atomic care
 502		 * is needed to avoid losing the dirty bit: it is easier to use
 503		 * mark_page_accessed().
 504		 */
 505		mark_page_accessed(page);
 506	}
 507	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
 508		/* Do not mlock pte-mapped THP */
 509		if (PageTransCompound(page))
 510			goto out;
 511
 512		/*
 513		 * The preliminary mapping check is mainly to avoid the
 514		 * pointless overhead of lock_page on the ZERO_PAGE
 515		 * which might bounce very badly if there is contention.
 516		 *
 517		 * If the page is already locked, we don't need to
 518		 * handle it now - vmscan will handle it later if and
 519		 * when it attempts to reclaim the page.
 520		 */
 521		if (page->mapping && trylock_page(page)) {
 522			lru_add_drain();  /* push cached pages to LRU */
 523			/*
 524			 * Because we lock page here, and migration is
 525			 * blocked by the pte's page reference, and we
 526			 * know the page is still mapped, we don't even
 527			 * need to check for file-cache page truncation.
 528			 */
 529			mlock_vma_page(page);
 530			unlock_page(page);
 531		}
 532	}
 533out:
 534	pte_unmap_unlock(ptep, ptl);
 535	return page;
 536no_page:
 537	pte_unmap_unlock(ptep, ptl);
 538	if (!pte_none(pte))
 539		return NULL;
 540	return no_page_table(vma, flags);
 541}
 542
 543static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 544				    unsigned long address, pud_t *pudp,
 545				    unsigned int flags,
 546				    struct follow_page_context *ctx)
 547{
 548	pmd_t *pmd, pmdval;
 549	spinlock_t *ptl;
 550	struct page *page;
 551	struct mm_struct *mm = vma->vm_mm;
 552
 553	pmd = pmd_offset(pudp, address);
 554	/*
 555	 * The READ_ONCE() will stabilize the pmdval in a register or
 556	 * on the stack so that it will stop changing under the code.
 557	 */
 558	pmdval = READ_ONCE(*pmd);
 559	if (pmd_none(pmdval))
 560		return no_page_table(vma, flags);
 561	if (pmd_huge(pmdval) && is_vm_hugetlb_page(vma)) {
 562		page = follow_huge_pmd(mm, address, pmd, flags);
 563		if (page)
 564			return page;
 565		return no_page_table(vma, flags);
 566	}
 567	if (is_hugepd(__hugepd(pmd_val(pmdval)))) {
 568		page = follow_huge_pd(vma, address,
 569				      __hugepd(pmd_val(pmdval)), flags,
 570				      PMD_SHIFT);
 571		if (page)
 572			return page;
 573		return no_page_table(vma, flags);
 574	}
 575retry:
 576	if (!pmd_present(pmdval)) {
 577		if (likely(!(flags & FOLL_MIGRATION)))
 578			return no_page_table(vma, flags);
 579		VM_BUG_ON(thp_migration_supported() &&
 580				  !is_pmd_migration_entry(pmdval));
 581		if (is_pmd_migration_entry(pmdval))
 582			pmd_migration_entry_wait(mm, pmd);
 583		pmdval = READ_ONCE(*pmd);
 584		/*
 585		 * MADV_DONTNEED may convert the pmd to null because
 586		 * mmap_lock is held in read mode
 587		 */
 588		if (pmd_none(pmdval))
 589			return no_page_table(vma, flags);
 590		goto retry;
 591	}
 592	if (pmd_devmap(pmdval)) {
 593		ptl = pmd_lock(mm, pmd);
 594		page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
 595		spin_unlock(ptl);
 596		if (page)
 597			return page;
 598	}
 599	if (likely(!pmd_trans_huge(pmdval)))
 600		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 601
 602	if ((flags & FOLL_NUMA) && pmd_protnone(pmdval))
 603		return no_page_table(vma, flags);
 604
 605retry_locked:
 606	ptl = pmd_lock(mm, pmd);
 607	if (unlikely(pmd_none(*pmd))) {
 608		spin_unlock(ptl);
 609		return no_page_table(vma, flags);
 610	}
 611	if (unlikely(!pmd_present(*pmd))) {
 612		spin_unlock(ptl);
 613		if (likely(!(flags & FOLL_MIGRATION)))
 614			return no_page_table(vma, flags);
 615		pmd_migration_entry_wait(mm, pmd);
 616		goto retry_locked;
 617	}
 618	if (unlikely(!pmd_trans_huge(*pmd))) {
 619		spin_unlock(ptl);
 620		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 621	}
 622	if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) {
 623		int ret;
 624		page = pmd_page(*pmd);
 625		if (is_huge_zero_page(page)) {
 626			spin_unlock(ptl);
 627			ret = 0;
 628			split_huge_pmd(vma, pmd, address);
 629			if (pmd_trans_unstable(pmd))
 630				ret = -EBUSY;
 631		} else if (flags & FOLL_SPLIT) {
 632			if (unlikely(!try_get_page(page))) {
 633				spin_unlock(ptl);
 634				return ERR_PTR(-ENOMEM);
 635			}
 636			spin_unlock(ptl);
 637			lock_page(page);
 638			ret = split_huge_page(page);
 639			unlock_page(page);
 640			put_page(page);
 641			if (pmd_none(*pmd))
 642				return no_page_table(vma, flags);
 643		} else {  /* flags & FOLL_SPLIT_PMD */
 644			spin_unlock(ptl);
 645			split_huge_pmd(vma, pmd, address);
 646			ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;
 647		}
 648
 649		return ret ? ERR_PTR(ret) :
 650			follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 651	}
 652	page = follow_trans_huge_pmd(vma, address, pmd, flags);
 653	spin_unlock(ptl);
 654	ctx->page_mask = HPAGE_PMD_NR - 1;
 655	return page;
 656}
 657
 658static struct page *follow_pud_mask(struct vm_area_struct *vma,
 659				    unsigned long address, p4d_t *p4dp,
 660				    unsigned int flags,
 661				    struct follow_page_context *ctx)
 662{
 663	pud_t *pud;
 664	spinlock_t *ptl;
 665	struct page *page;
 666	struct mm_struct *mm = vma->vm_mm;
 667
 668	pud = pud_offset(p4dp, address);
 669	if (pud_none(*pud))
 670		return no_page_table(vma, flags);
 671	if (pud_huge(*pud) && is_vm_hugetlb_page(vma)) {
 672		page = follow_huge_pud(mm, address, pud, flags);
 673		if (page)
 674			return page;
 675		return no_page_table(vma, flags);
 676	}
 677	if (is_hugepd(__hugepd(pud_val(*pud)))) {
 678		page = follow_huge_pd(vma, address,
 679				      __hugepd(pud_val(*pud)), flags,
 680				      PUD_SHIFT);
 681		if (page)
 682			return page;
 683		return no_page_table(vma, flags);
 684	}
 685	if (pud_devmap(*pud)) {
 686		ptl = pud_lock(mm, pud);
 687		page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
 688		spin_unlock(ptl);
 689		if (page)
 690			return page;
 691	}
 692	if (unlikely(pud_bad(*pud)))
 693		return no_page_table(vma, flags);
 694
 695	return follow_pmd_mask(vma, address, pud, flags, ctx);
 696}
 697
 698static struct page *follow_p4d_mask(struct vm_area_struct *vma,
 699				    unsigned long address, pgd_t *pgdp,
 700				    unsigned int flags,
 701				    struct follow_page_context *ctx)
 702{
 703	p4d_t *p4d;
 704	struct page *page;
 705
 706	p4d = p4d_offset(pgdp, address);
 707	if (p4d_none(*p4d))
 708		return no_page_table(vma, flags);
 709	BUILD_BUG_ON(p4d_huge(*p4d));
 710	if (unlikely(p4d_bad(*p4d)))
 711		return no_page_table(vma, flags);
 712
 713	if (is_hugepd(__hugepd(p4d_val(*p4d)))) {
 714		page = follow_huge_pd(vma, address,
 715				      __hugepd(p4d_val(*p4d)), flags,
 716				      P4D_SHIFT);
 717		if (page)
 718			return page;
 719		return no_page_table(vma, flags);
 720	}
 721	return follow_pud_mask(vma, address, p4d, flags, ctx);
 722}
 723
 724/**
 725 * follow_page_mask - look up a page descriptor from a user-virtual address
 726 * @vma: vm_area_struct mapping @address
 727 * @address: virtual address to look up
 728 * @flags: flags modifying lookup behaviour
 729 * @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
 730 *       pointer to output page_mask
 731 *
 732 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 733 *
 734 * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
 735 * the device's dev_pagemap metadata to avoid repeating expensive lookups.
 736 *
 737 * On output, the @ctx->page_mask is set according to the size of the page.
 738 *
 739 * Return: the mapped (struct page *), %NULL if no mapping exists, or
 740 * an error pointer if there is a mapping to something not represented
 741 * by a page descriptor (see also vm_normal_page()).
 742 */
 743static struct page *follow_page_mask(struct vm_area_struct *vma,
 744			      unsigned long address, unsigned int flags,
 745			      struct follow_page_context *ctx)
 746{
 747	pgd_t *pgd;
 748	struct page *page;
 749	struct mm_struct *mm = vma->vm_mm;
 750
 751	ctx->page_mask = 0;
 752
 753	/* make this handle hugepd */
 754	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
 755	if (!IS_ERR(page)) {
 756		WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN));
 757		return page;
 758	}
 759
 760	pgd = pgd_offset(mm, address);
 761
 762	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
 763		return no_page_table(vma, flags);
 764
 765	if (pgd_huge(*pgd)) {
 766		page = follow_huge_pgd(mm, address, pgd, flags);
 767		if (page)
 768			return page;
 769		return no_page_table(vma, flags);
 770	}
 771	if (is_hugepd(__hugepd(pgd_val(*pgd)))) {
 772		page = follow_huge_pd(vma, address,
 773				      __hugepd(pgd_val(*pgd)), flags,
 774				      PGDIR_SHIFT);
 775		if (page)
 776			return page;
 777		return no_page_table(vma, flags);
 778	}
 779
 780	return follow_p4d_mask(vma, address, pgd, flags, ctx);
 781}
 782
 783struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 784			 unsigned int foll_flags)
 785{
 786	struct follow_page_context ctx = { NULL };
 787	struct page *page;
 788
 789	page = follow_page_mask(vma, address, foll_flags, &ctx);
 790	if (ctx.pgmap)
 791		put_dev_pagemap(ctx.pgmap);
 792	return page;
 793}
 794
 795static int get_gate_page(struct mm_struct *mm, unsigned long address,
 796		unsigned int gup_flags, struct vm_area_struct **vma,
 797		struct page **page)
 798{
 799	pgd_t *pgd;
 800	p4d_t *p4d;
 801	pud_t *pud;
 802	pmd_t *pmd;
 803	pte_t *pte;
 804	int ret = -EFAULT;
 805
 806	/* user gate pages are read-only */
 807	if (gup_flags & FOLL_WRITE)
 808		return -EFAULT;
 809	if (address > TASK_SIZE)
 810		pgd = pgd_offset_k(address);
 811	else
 812		pgd = pgd_offset_gate(mm, address);
 813	if (pgd_none(*pgd))
 814		return -EFAULT;
 815	p4d = p4d_offset(pgd, address);
 816	if (p4d_none(*p4d))
 817		return -EFAULT;
 818	pud = pud_offset(p4d, address);
 819	if (pud_none(*pud))
 820		return -EFAULT;
 821	pmd = pmd_offset(pud, address);
 822	if (!pmd_present(*pmd))
 823		return -EFAULT;
 824	VM_BUG_ON(pmd_trans_huge(*pmd));
 825	pte = pte_offset_map(pmd, address);
 826	if (pte_none(*pte))
 827		goto unmap;
 828	*vma = get_gate_vma(mm);
 829	if (!page)
 830		goto out;
 831	*page = vm_normal_page(*vma, address, *pte);
 832	if (!*page) {
 833		if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
 834			goto unmap;
 835		*page = pte_page(*pte);
 836	}
 837	if (unlikely(!try_grab_page(*page, gup_flags))) {
 838		ret = -ENOMEM;
 839		goto unmap;
 840	}
 841out:
 842	ret = 0;
 843unmap:
 844	pte_unmap(pte);
 845	return ret;
 846}
 847
 848/*
 849 * mmap_lock must be held on entry.  If @locked != NULL and *@flags
 850 * does not include FOLL_NOWAIT, the mmap_lock may be released.  If it
 851 * is, *@locked will be set to 0 and -EBUSY returned.
 852 */
 853static int faultin_page(struct vm_area_struct *vma,
 854		unsigned long address, unsigned int *flags, int *locked)
 855{
 856	unsigned int fault_flags = 0;
 857	vm_fault_t ret;
 858
 859	/* mlock all present pages, but do not fault in new pages */
 860	if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
 861		return -ENOENT;
 862	if (*flags & FOLL_WRITE)
 863		fault_flags |= FAULT_FLAG_WRITE;
 864	if (*flags & FOLL_REMOTE)
 865		fault_flags |= FAULT_FLAG_REMOTE;
 866	if (locked)
 867		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 868	if (*flags & FOLL_NOWAIT)
 869		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 870	if (*flags & FOLL_TRIED) {
 871		/*
 872		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
 873		 * can co-exist
 874		 */
 875		fault_flags |= FAULT_FLAG_TRIED;
 876	}
 877
 878	ret = handle_mm_fault(vma, address, fault_flags, NULL);
 879	if (ret & VM_FAULT_ERROR) {
 880		int err = vm_fault_to_errno(ret, *flags);
 881
 882		if (err)
 883			return err;
 884		BUG();
 885	}
 886
 887	if (ret & VM_FAULT_RETRY) {
 888		if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
 889			*locked = 0;
 890		return -EBUSY;
 891	}
 892
 893	/*
 894	 * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
 895	 * necessary, even if maybe_mkwrite decided not to set pte_write. We
 896	 * can thus safely do subsequent page lookups as if they were reads.
 897	 * But only do so when looping for pte_write is futile: in some cases
 898	 * userspace may also be wanting to write to the gotten user page,
 899	 * which a read fault here might prevent (a readonly page might get
 900	 * reCOWed by userspace write).
 901	 */
 902	if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
 903		*flags |= FOLL_COW;
 904	return 0;
 905}
 906
 907static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 908{
 909	vm_flags_t vm_flags = vma->vm_flags;
 910	int write = (gup_flags & FOLL_WRITE);
 911	int foreign = (gup_flags & FOLL_REMOTE);
 912
 913	if (vm_flags & (VM_IO | VM_PFNMAP))
 914		return -EFAULT;
 915
 916	if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
 917		return -EFAULT;
 918
 919	if (write) {
 920		if (!(vm_flags & VM_WRITE)) {
 921			if (!(gup_flags & FOLL_FORCE))
 922				return -EFAULT;
 923			/*
 924			 * We used to let the write,force case do COW in a
 925			 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
 926			 * set a breakpoint in a read-only mapping of an
 927			 * executable, without corrupting the file (yet only
 928			 * when that file had been opened for writing!).
 929			 * Anon pages in shared mappings are surprising: now
 930			 * just reject it.
 931			 */
 932			if (!is_cow_mapping(vm_flags))
 933				return -EFAULT;
 934		}
 935	} else if (!(vm_flags & VM_READ)) {
 936		if (!(gup_flags & FOLL_FORCE))
 937			return -EFAULT;
 938		/*
 939		 * Is there actually any vma we can reach here which does not
 940		 * have VM_MAYREAD set?
 941		 */
 942		if (!(vm_flags & VM_MAYREAD))
 943			return -EFAULT;
 944	}
 945	/*
 946	 * gups are always data accesses, not instruction
 947	 * fetches, so execute=false here
 948	 */
 949	if (!arch_vma_access_permitted(vma, write, false, foreign))
 950		return -EFAULT;
 951	return 0;
 952}
 953
 954/**
 955 * __get_user_pages() - pin user pages in memory
 956 * @mm:		mm_struct of target mm
 957 * @start:	starting user address
 958 * @nr_pages:	number of pages from start to pin
 959 * @gup_flags:	flags modifying pin behaviour
 960 * @pages:	array that receives pointers to the pages pinned.
 961 *		Should be at least nr_pages long. Or NULL, if caller
 962 *		only intends to ensure the pages are faulted in.
 963 * @vmas:	array of pointers to vmas corresponding to each page.
 964 *		Or NULL if the caller does not require them.
 965 * @locked:     whether we're still with the mmap_lock held
 966 *
 967 * Returns either number of pages pinned (which may be less than the
 968 * number requested), or an error. Details about the return value:
 969 *
 970 * -- If nr_pages is 0, returns 0.
 971 * -- If nr_pages is >0, but no pages were pinned, returns -errno.
 972 * -- If nr_pages is >0, and some pages were pinned, returns the number of
 973 *    pages pinned. Again, this may be less than nr_pages.
 974 * -- 0 return value is possible when the fault would need to be retried.
 975 *
 976 * The caller is responsible for releasing returned @pages, via put_page().
 977 *
 978 * @vmas are valid only as long as mmap_lock is held.
 979 *
 980 * Must be called with mmap_lock held.  It may be released.  See below.
 981 *
 982 * __get_user_pages walks a process's page tables and takes a reference to
 983 * each struct page that each user address corresponds to at a given
 984 * instant. That is, it takes the page that would be accessed if a user
 985 * thread accesses the given user virtual address at that instant.
 986 *
 987 * This does not guarantee that the page exists in the user mappings when
 988 * __get_user_pages returns, and there may even be a completely different
 989 * page there in some cases (eg. if mmapped pagecache has been invalidated
 990 * and subsequently re faulted). However it does guarantee that the page
 991 * won't be freed completely. And mostly callers simply care that the page
 992 * contains data that was valid *at some point in time*. Typically, an IO
 993 * or similar operation cannot guarantee anything stronger anyway because
 994 * locks can't be held over the syscall boundary.
 995 *
 996 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
 997 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
 998 * appropriate) must be called after the page is finished with, and
 999 * before put_page is called.
1000 *
1001 * If @locked != NULL, *@locked will be set to 0 when mmap_lock is
1002 * released by an up_read().  That can happen if @gup_flags does not
1003 * have FOLL_NOWAIT.
1004 *
1005 * A caller using such a combination of @locked and @gup_flags
1006 * must therefore hold the mmap_lock for reading only, and recognize
1007 * when it's been released.  Otherwise, it must be held for either
1008 * reading or writing and will not be released.
1009 *
1010 * In most cases, get_user_pages or get_user_pages_fast should be used
1011 * instead of __get_user_pages. __get_user_pages should be used only if
1012 * you need some special @gup_flags.
1013 */
1014static long __get_user_pages(struct mm_struct *mm,
1015		unsigned long start, unsigned long nr_pages,
1016		unsigned int gup_flags, struct page **pages,
1017		struct vm_area_struct **vmas, int *locked)
1018{
1019	long ret = 0, i = 0;
1020	struct vm_area_struct *vma = NULL;
1021	struct follow_page_context ctx = { NULL };
1022
1023	if (!nr_pages)
1024		return 0;
1025
1026	start = untagged_addr(start);
1027
1028	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
1029
1030	/*
1031	 * If FOLL_FORCE is set then do not force a full fault as the hinting
1032	 * fault information is unrelated to the reference behaviour of a task
1033	 * using the address space
1034	 */
1035	if (!(gup_flags & FOLL_FORCE))
1036		gup_flags |= FOLL_NUMA;
1037
1038	do {
1039		struct page *page;
1040		unsigned int foll_flags = gup_flags;
1041		unsigned int page_increm;
1042
1043		/* first iteration or cross vma bound */
1044		if (!vma || start >= vma->vm_end) {
1045			vma = find_extend_vma(mm, start);
1046			if (!vma && in_gate_area(mm, start)) {
1047				ret = get_gate_page(mm, start & PAGE_MASK,
1048						gup_flags, &vma,
1049						pages ? &pages[i] : NULL);
1050				if (ret)
1051					goto out;
1052				ctx.page_mask = 0;
1053				goto next_page;
1054			}
1055
1056			if (!vma || check_vma_flags(vma, gup_flags)) {
1057				ret = -EFAULT;
1058				goto out;
1059			}
1060			if (is_vm_hugetlb_page(vma)) {
1061				i = follow_hugetlb_page(mm, vma, pages, vmas,
1062						&start, &nr_pages, i,
1063						gup_flags, locked);
1064				if (locked && *locked == 0) {
1065					/*
1066					 * We've got a VM_FAULT_RETRY
1067					 * and we've lost mmap_lock.
1068					 * We must stop here.
1069					 */
1070					BUG_ON(gup_flags & FOLL_NOWAIT);
1071					BUG_ON(ret != 0);
1072					goto out;
1073				}
1074				continue;
1075			}
1076		}
1077retry:
1078		/*
1079		 * If we have a pending SIGKILL, don't keep faulting pages and
1080		 * potentially allocating memory.
1081		 */
1082		if (fatal_signal_pending(current)) {
1083			ret = -EINTR;
1084			goto out;
1085		}
1086		cond_resched();
1087
1088		page = follow_page_mask(vma, start, foll_flags, &ctx);
1089		if (!page) {
1090			ret = faultin_page(vma, start, &foll_flags, locked);
1091			switch (ret) {
1092			case 0:
1093				goto retry;
1094			case -EBUSY:
1095				ret = 0;
1096				fallthrough;
1097			case -EFAULT:
1098			case -ENOMEM:
1099			case -EHWPOISON:
1100				goto out;
1101			case -ENOENT:
1102				goto next_page;
1103			}
1104			BUG();
1105		} else if (PTR_ERR(page) == -EEXIST) {
1106			/*
1107			 * Proper page table entry exists, but no corresponding
1108			 * struct page.
1109			 */
1110			goto next_page;
1111		} else if (IS_ERR(page)) {
1112			ret = PTR_ERR(page);
1113			goto out;
1114		}
1115		if (pages) {
1116			pages[i] = page;
1117			flush_anon_page(vma, page, start);
1118			flush_dcache_page(page);
1119			ctx.page_mask = 0;
1120		}
1121next_page:
1122		if (vmas) {
1123			vmas[i] = vma;
1124			ctx.page_mask = 0;
1125		}
1126		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
1127		if (page_increm > nr_pages)
1128			page_increm = nr_pages;
1129		i += page_increm;
1130		start += page_increm * PAGE_SIZE;
1131		nr_pages -= page_increm;
1132	} while (nr_pages);
1133out:
1134	if (ctx.pgmap)
1135		put_dev_pagemap(ctx.pgmap);
1136	return i ? i : ret;
1137}
1138
1139static bool vma_permits_fault(struct vm_area_struct *vma,
1140			      unsigned int fault_flags)
1141{
1142	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
1143	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
1144	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
1145
1146	if (!(vm_flags & vma->vm_flags))
1147		return false;
1148
1149	/*
1150	 * The architecture might have a hardware protection
1151	 * mechanism other than read/write that can deny access.
1152	 *
1153	 * gup always represents data access, not instruction
1154	 * fetches, so execute=false here:
1155	 */
1156	if (!arch_vma_access_permitted(vma, write, false, foreign))
1157		return false;
1158
1159	return true;
1160}
1161
1162/**
1163 * fixup_user_fault() - manually resolve a user page fault
1164 * @mm:		mm_struct of target mm
1165 * @address:	user address
1166 * @fault_flags:flags to pass down to handle_mm_fault()
1167 * @unlocked:	did we unlock the mmap_lock while retrying, maybe NULL if caller
1168 *		does not allow retry. If NULL, the caller must guarantee
1169 *		that fault_flags does not contain FAULT_FLAG_ALLOW_RETRY.
1170 *
1171 * This is meant to be called in the specific scenario where for locking reasons
1172 * we try to access user memory in atomic context (within a pagefault_disable()
1173 * section), this returns -EFAULT, and we want to resolve the user fault before
1174 * trying again.
1175 *
1176 * Typically this is meant to be used by the futex code.
1177 *
1178 * The main difference with get_user_pages() is that this function will
1179 * unconditionally call handle_mm_fault() which will in turn perform all the
1180 * necessary SW fixup of the dirty and young bits in the PTE, while
1181 * get_user_pages() only guarantees to update these in the struct page.
1182 *
1183 * This is important for some architectures where those bits also gate the
1184 * access permission to the page because they are maintained in software.  On
1185 * such architectures, gup() will not be enough to make a subsequent access
1186 * succeed.
1187 *
1188 * This function will not return with an unlocked mmap_lock. So it has not the
1189 * same semantics wrt the @mm->mmap_lock as does filemap_fault().
1190 */
1191int fixup_user_fault(struct mm_struct *mm,
1192		     unsigned long address, unsigned int fault_flags,
1193		     bool *unlocked)
1194{
1195	struct vm_area_struct *vma;
1196	vm_fault_t ret, major = 0;
1197
1198	address = untagged_addr(address);
1199
1200	if (unlocked)
1201		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1202
1203retry:
1204	vma = find_extend_vma(mm, address);
1205	if (!vma || address < vma->vm_start)
1206		return -EFAULT;
1207
1208	if (!vma_permits_fault(vma, fault_flags))
1209		return -EFAULT;
1210
1211	if ((fault_flags & FAULT_FLAG_KILLABLE) &&
1212	    fatal_signal_pending(current))
1213		return -EINTR;
1214
1215	ret = handle_mm_fault(vma, address, fault_flags, NULL);
1216	major |= ret & VM_FAULT_MAJOR;
1217	if (ret & VM_FAULT_ERROR) {
1218		int err = vm_fault_to_errno(ret, 0);
1219
1220		if (err)
1221			return err;
1222		BUG();
1223	}
1224
1225	if (ret & VM_FAULT_RETRY) {
1226		mmap_read_lock(mm);
1227		*unlocked = true;
1228		fault_flags |= FAULT_FLAG_TRIED;
1229		goto retry;
1230	}
1231
1232	return 0;
1233}
1234EXPORT_SYMBOL_GPL(fixup_user_fault);
1235
1236/*
1237 * Please note that this function, unlike __get_user_pages will not
1238 * return 0 for nr_pages > 0 without FOLL_NOWAIT
1239 */
1240static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
1241						unsigned long start,
1242						unsigned long nr_pages,
1243						struct page **pages,
1244						struct vm_area_struct **vmas,
1245						int *locked,
1246						unsigned int flags)
1247{
1248	long ret, pages_done;
1249	bool lock_dropped;
1250
1251	if (locked) {
1252		/* if VM_FAULT_RETRY can be returned, vmas become invalid */
1253		BUG_ON(vmas);
1254		/* check caller initialized locked */
1255		BUG_ON(*locked != 1);
1256	}
1257
1258	if (flags & FOLL_PIN)
1259		atomic_set(&mm->has_pinned, 1);
1260
1261	/*
1262	 * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior
1263	 * is to set FOLL_GET if the caller wants pages[] filled in (but has
1264	 * carelessly failed to specify FOLL_GET), so keep doing that, but only
1265	 * for FOLL_GET, not for the newer FOLL_PIN.
1266	 *
1267	 * FOLL_PIN always expects pages to be non-null, but no need to assert
1268	 * that here, as any failures will be obvious enough.
1269	 */
1270	if (pages && !(flags & FOLL_PIN))
1271		flags |= FOLL_GET;
1272
1273	pages_done = 0;
1274	lock_dropped = false;
1275	for (;;) {
1276		ret = __get_user_pages(mm, start, nr_pages, flags, pages,
1277				       vmas, locked);
1278		if (!locked)
1279			/* VM_FAULT_RETRY couldn't trigger, bypass */
1280			return ret;
1281
1282		/* VM_FAULT_RETRY cannot return errors */
1283		if (!*locked) {
1284			BUG_ON(ret < 0);
1285			BUG_ON(ret >= nr_pages);
1286		}
1287
1288		if (ret > 0) {
1289			nr_pages -= ret;
1290			pages_done += ret;
1291			if (!nr_pages)
1292				break;
1293		}
1294		if (*locked) {
1295			/*
1296			 * VM_FAULT_RETRY didn't trigger or it was a
1297			 * FOLL_NOWAIT.
1298			 */
1299			if (!pages_done)
1300				pages_done = ret;
1301			break;
1302		}
1303		/*
1304		 * VM_FAULT_RETRY triggered, so seek to the faulting offset.
1305		 * For the prefault case (!pages) we only update counts.
1306		 */
1307		if (likely(pages))
1308			pages += ret;
1309		start += ret << PAGE_SHIFT;
1310		lock_dropped = true;
1311
1312retry:
1313		/*
1314		 * Repeat on the address that fired VM_FAULT_RETRY
1315		 * with both FAULT_FLAG_ALLOW_RETRY and
1316		 * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
1317		 * by fatal signals, so we need to check it before we
1318		 * start trying again otherwise it can loop forever.
1319		 */
1320
1321		if (fatal_signal_pending(current)) {
1322			if (!pages_done)
1323				pages_done = -EINTR;
1324			break;
1325		}
1326
1327		ret = mmap_read_lock_killable(mm);
1328		if (ret) {
1329			BUG_ON(ret > 0);
1330			if (!pages_done)
1331				pages_done = ret;
1332			break;
1333		}
1334
1335		*locked = 1;
1336		ret = __get_user_pages(mm, start, 1, flags | FOLL_TRIED,
1337				       pages, NULL, locked);
1338		if (!*locked) {
1339			/* Continue to retry until we succeeded */
1340			BUG_ON(ret != 0);
1341			goto retry;
1342		}
1343		if (ret != 1) {
1344			BUG_ON(ret > 1);
1345			if (!pages_done)
1346				pages_done = ret;
1347			break;
1348		}
1349		nr_pages--;
1350		pages_done++;
1351		if (!nr_pages)
1352			break;
1353		if (likely(pages))
1354			pages++;
1355		start += PAGE_SIZE;
1356	}
1357	if (lock_dropped && *locked) {
1358		/*
1359		 * We must let the caller know we temporarily dropped the lock
1360		 * and so the critical section protected by it was lost.
1361		 */
1362		mmap_read_unlock(mm);
1363		*locked = 0;
1364	}
1365	return pages_done;
1366}
1367
1368/**
1369 * populate_vma_page_range() -  populate a range of pages in the vma.
1370 * @vma:   target vma
1371 * @start: start address
1372 * @end:   end address
1373 * @locked: whether the mmap_lock is still held
1374 *
1375 * This takes care of mlocking the pages too if VM_LOCKED is set.
1376 *
1377 * Return either number of pages pinned in the vma, or a negative error
1378 * code on error.
1379 *
1380 * vma->vm_mm->mmap_lock must be held.
1381 *
1382 * If @locked is NULL, it may be held for read or write and will
1383 * be unperturbed.
1384 *
1385 * If @locked is non-NULL, it must held for read only and may be
1386 * released.  If it's released, *@locked will be set to 0.
1387 */
1388long populate_vma_page_range(struct vm_area_struct *vma,
1389		unsigned long start, unsigned long end, int *locked)
1390{
1391	struct mm_struct *mm = vma->vm_mm;
1392	unsigned long nr_pages = (end - start) / PAGE_SIZE;
1393	int gup_flags;
1394
1395	VM_BUG_ON(start & ~PAGE_MASK);
1396	VM_BUG_ON(end   & ~PAGE_MASK);
1397	VM_BUG_ON_VMA(start < vma->vm_start, vma);
1398	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
1399	mmap_assert_locked(mm);
1400
1401	gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
1402	if (vma->vm_flags & VM_LOCKONFAULT)
1403		gup_flags &= ~FOLL_POPULATE;
1404	/*
1405	 * We want to touch writable mappings with a write fault in order
1406	 * to break COW, except for shared mappings because these don't COW
1407	 * and we would not want to dirty them for nothing.
1408	 */
1409	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
1410		gup_flags |= FOLL_WRITE;
1411
1412	/*
1413	 * We want mlock to succeed for regions that have any permissions
1414	 * other than PROT_NONE.
1415	 */
1416	if (vma_is_accessible(vma))
1417		gup_flags |= FOLL_FORCE;
1418
1419	/*
1420	 * We made sure addr is within a VMA, so the following will
1421	 * not result in a stack expansion that recurses back here.
1422	 */
1423	return __get_user_pages(mm, start, nr_pages, gup_flags,
1424				NULL, NULL, locked);
1425}
1426
1427/*
1428 * __mm_populate - populate and/or mlock pages within a range of address space.
1429 *
1430 * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
1431 * flags. VMAs must be already marked with the desired vm_flags, and
1432 * mmap_lock must not be held.
1433 */
1434int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
1435{
1436	struct mm_struct *mm = current->mm;
1437	unsigned long end, nstart, nend;
1438	struct vm_area_struct *vma = NULL;
1439	int locked = 0;
1440	long ret = 0;
1441
1442	end = start + len;
1443
1444	for (nstart = start; nstart < end; nstart = nend) {
1445		/*
1446		 * We want to fault in pages for [nstart; end) address range.
1447		 * Find first corresponding VMA.
1448		 */
1449		if (!locked) {
1450			locked = 1;
1451			mmap_read_lock(mm);
1452			vma = find_vma(mm, nstart);
1453		} else if (nstart >= vma->vm_end)
1454			vma = vma->vm_next;
1455		if (!vma || vma->vm_start >= end)
1456			break;
1457		/*
1458		 * Set [nstart; nend) to intersection of desired address
1459		 * range with the first VMA. Also, skip undesirable VMA types.
1460		 */
1461		nend = min(end, vma->vm_end);
1462		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
1463			continue;
1464		if (nstart < vma->vm_start)
1465			nstart = vma->vm_start;
1466		/*
1467		 * Now fault in a range of pages. populate_vma_page_range()
1468		 * double checks the vma flags, so that it won't mlock pages
1469		 * if the vma was already munlocked.
1470		 */
1471		ret = populate_vma_page_range(vma, nstart, nend, &locked);
1472		if (ret < 0) {
1473			if (ignore_errors) {
1474				ret = 0;
1475				continue;	/* continue at next VMA */
1476			}
1477			break;
1478		}
1479		nend = nstart + ret * PAGE_SIZE;
1480		ret = 0;
1481	}
1482	if (locked)
1483		mmap_read_unlock(mm);
1484	return ret;	/* 0 or negative error code */
1485}
1486
1487/**
1488 * get_dump_page() - pin user page in memory while writing it to core dump
1489 * @addr: user address
1490 *
1491 * Returns struct page pointer of user page pinned for dump,
1492 * to be freed afterwards by put_page().
1493 *
1494 * Returns NULL on any kind of failure - a hole must then be inserted into
1495 * the corefile, to preserve alignment with its headers; and also returns
1496 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
1497 * allowing a hole to be left in the corefile to save diskspace.
1498 *
1499 * Called without mmap_lock, but after all other threads have been killed.
1500 */
1501#ifdef CONFIG_ELF_CORE
1502struct page *get_dump_page(unsigned long addr)
1503{
1504	struct vm_area_struct *vma;
1505	struct page *page;
1506
1507	if (__get_user_pages(current->mm, addr, 1,
1508			     FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
1509			     NULL) < 1)
1510		return NULL;
1511	flush_cache_page(vma, addr, page_to_pfn(page));
1512	return page;
1513}
1514#endif /* CONFIG_ELF_CORE */
1515#else /* CONFIG_MMU */
1516static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
1517		unsigned long nr_pages, struct page **pages,
1518		struct vm_area_struct **vmas, int *locked,
1519		unsigned int foll_flags)
1520{
1521	struct vm_area_struct *vma;
1522	unsigned long vm_flags;
1523	int i;
1524
1525	/* calculate required read or write permissions.
1526	 * If FOLL_FORCE is set, we only require the "MAY" flags.
1527	 */
1528	vm_flags  = (foll_flags & FOLL_WRITE) ?
1529			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
1530	vm_flags &= (foll_flags & FOLL_FORCE) ?
1531			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
1532
1533	for (i = 0; i < nr_pages; i++) {
1534		vma = find_vma(mm, start);
1535		if (!vma)
1536			goto finish_or_fault;
1537
1538		/* protect what we can, including chardevs */
1539		if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
1540		    !(vm_flags & vma->vm_flags))
1541			goto finish_or_fault;
1542
1543		if (pages) {
1544			pages[i] = virt_to_page(start);
1545			if (pages[i])
1546				get_page(pages[i]);
1547		}
1548		if (vmas)
1549			vmas[i] = vma;
1550		start = (start + PAGE_SIZE) & PAGE_MASK;
1551	}
1552
1553	return i;
1554
1555finish_or_fault:
1556	return i ? : -EFAULT;
1557}
1558#endif /* !CONFIG_MMU */
1559
1560#if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
1561static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
1562{
1563	long i;
1564	struct vm_area_struct *vma_prev = NULL;
1565
1566	for (i = 0; i < nr_pages; i++) {
1567		struct vm_area_struct *vma = vmas[i];
1568
1569		if (vma == vma_prev)
1570			continue;
1571
1572		vma_prev = vma;
1573
1574		if (vma_is_fsdax(vma))
1575			return true;
1576	}
1577	return false;
1578}
1579
1580#ifdef CONFIG_CMA
1581static long check_and_migrate_cma_pages(struct mm_struct *mm,
1582					unsigned long start,
1583					unsigned long nr_pages,
1584					struct page **pages,
1585					struct vm_area_struct **vmas,
1586					unsigned int gup_flags)
1587{
1588	unsigned long i;
1589	unsigned long step;
1590	bool drain_allow = true;
1591	bool migrate_allow = true;
1592	LIST_HEAD(cma_page_list);
1593	long ret = nr_pages;
1594	struct migration_target_control mtc = {
1595		.nid = NUMA_NO_NODE,
1596		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_NOWARN,
1597	};
1598
1599check_again:
1600	for (i = 0; i < nr_pages;) {
1601
1602		struct page *head = compound_head(pages[i]);
1603
1604		/*
1605		 * gup may start from a tail page. Advance step by the left
1606		 * part.
1607		 */
1608		step = compound_nr(head) - (pages[i] - head);
1609		/*
1610		 * If we get a page from the CMA zone, since we are going to
1611		 * be pinning these entries, we might as well move them out
1612		 * of the CMA zone if possible.
1613		 */
1614		if (is_migrate_cma_page(head)) {
1615			if (PageHuge(head))
1616				isolate_huge_page(head, &cma_page_list);
1617			else {
1618				if (!PageLRU(head) && drain_allow) {
1619					lru_add_drain_all();
1620					drain_allow = false;
1621				}
1622
1623				if (!isolate_lru_page(head)) {
1624					list_add_tail(&head->lru, &cma_page_list);
1625					mod_node_page_state(page_pgdat(head),
1626							    NR_ISOLATED_ANON +
1627							    page_is_file_lru(head),
1628							    thp_nr_pages(head));
1629				}
1630			}
1631		}
1632
1633		i += step;
1634	}
1635
1636	if (!list_empty(&cma_page_list)) {
1637		/*
1638		 * drop the above get_user_pages reference.
1639		 */
1640		for (i = 0; i < nr_pages; i++)
1641			put_page(pages[i]);
1642
1643		if (migrate_pages(&cma_page_list, alloc_migration_target, NULL,
1644			(unsigned long)&mtc, MIGRATE_SYNC, MR_CONTIG_RANGE)) {
1645			/*
1646			 * some of the pages failed migration. Do get_user_pages
1647			 * without migration.
1648			 */
1649			migrate_allow = false;
1650
1651			if (!list_empty(&cma_page_list))
1652				putback_movable_pages(&cma_page_list);
1653		}
1654		/*
1655		 * We did migrate all the pages, Try to get the page references
1656		 * again migrating any new CMA pages which we failed to isolate
1657		 * earlier.
1658		 */
1659		ret = __get_user_pages_locked(mm, start, nr_pages,
1660						   pages, vmas, NULL,
1661						   gup_flags);
1662
1663		if ((ret > 0) && migrate_allow) {
1664			nr_pages = ret;
1665			drain_allow = true;
1666			goto check_again;
1667		}
1668	}
1669
1670	return ret;
1671}
1672#else
1673static long check_and_migrate_cma_pages(struct mm_struct *mm,
1674					unsigned long start,
1675					unsigned long nr_pages,
1676					struct page **pages,
1677					struct vm_area_struct **vmas,
1678					unsigned int gup_flags)
1679{
1680	return nr_pages;
1681}
1682#endif /* CONFIG_CMA */
1683
1684/*
1685 * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
1686 * allows us to process the FOLL_LONGTERM flag.
1687 */
1688static long __gup_longterm_locked(struct mm_struct *mm,
1689				  unsigned long start,
1690				  unsigned long nr_pages,
1691				  struct page **pages,
1692				  struct vm_area_struct **vmas,
1693				  unsigned int gup_flags)
1694{
1695	struct vm_area_struct **vmas_tmp = vmas;
1696	unsigned long flags = 0;
1697	long rc, i;
1698
1699	if (gup_flags & FOLL_LONGTERM) {
1700		if (!pages)
1701			return -EINVAL;
1702
1703		if (!vmas_tmp) {
1704			vmas_tmp = kcalloc(nr_pages,
1705					   sizeof(struct vm_area_struct *),
1706					   GFP_KERNEL);
1707			if (!vmas_tmp)
1708				return -ENOMEM;
1709		}
1710		flags = memalloc_nocma_save();
1711	}
1712
1713	rc = __get_user_pages_locked(mm, start, nr_pages, pages,
1714				     vmas_tmp, NULL, gup_flags);
1715
1716	if (gup_flags & FOLL_LONGTERM) {
1717		if (rc < 0)
1718			goto out;
1719
1720		if (check_dax_vmas(vmas_tmp, rc)) {
1721			for (i = 0; i < rc; i++)
1722				put_page(pages[i]);
1723			rc = -EOPNOTSUPP;
1724			goto out;
1725		}
1726
1727		rc = check_and_migrate_cma_pages(mm, start, rc, pages,
1728						 vmas_tmp, gup_flags);
1729out:
1730		memalloc_nocma_restore(flags);
1731	}
1732
1733	if (vmas_tmp != vmas)
1734		kfree(vmas_tmp);
1735	return rc;
1736}
1737#else /* !CONFIG_FS_DAX && !CONFIG_CMA */
1738static __always_inline long __gup_longterm_locked(struct mm_struct *mm,
1739						  unsigned long start,
1740						  unsigned long nr_pages,
1741						  struct page **pages,
1742						  struct vm_area_struct **vmas,
1743						  unsigned int flags)
1744{
1745	return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
1746				       NULL, flags);
1747}
1748#endif /* CONFIG_FS_DAX || CONFIG_CMA */
1749
1750#ifdef CONFIG_MMU
1751static long __get_user_pages_remote(struct mm_struct *mm,
1752				    unsigned long start, unsigned long nr_pages,
1753				    unsigned int gup_flags, struct page **pages,
1754				    struct vm_area_struct **vmas, int *locked)
1755{
1756	/*
1757	 * Parts of FOLL_LONGTERM behavior are incompatible with
1758	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
1759	 * vmas. However, this only comes up if locked is set, and there are
1760	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
1761	 * allow what we can.
1762	 */
1763	if (gup_flags & FOLL_LONGTERM) {
1764		if (WARN_ON_ONCE(locked))
1765			return -EINVAL;
1766		/*
1767		 * This will check the vmas (even if our vmas arg is NULL)
1768		 * and return -ENOTSUPP if DAX isn't allowed in this case:
1769		 */
1770		return __gup_longterm_locked(mm, start, nr_pages, pages,
1771					     vmas, gup_flags | FOLL_TOUCH |
1772					     FOLL_REMOTE);
1773	}
1774
1775	return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
1776				       locked,
1777				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
1778}
1779
1780/**
1781 * get_user_pages_remote() - pin user pages in memory
1782 * @mm:		mm_struct of target mm
1783 * @start:	starting user address
1784 * @nr_pages:	number of pages from start to pin
1785 * @gup_flags:	flags modifying lookup behaviour
1786 * @pages:	array that receives pointers to the pages pinned.
1787 *		Should be at least nr_pages long. Or NULL, if caller
1788 *		only intends to ensure the pages are faulted in.
1789 * @vmas:	array of pointers to vmas corresponding to each page.
1790 *		Or NULL if the caller does not require them.
1791 * @locked:	pointer to lock flag indicating whether lock is held and
1792 *		subsequently whether VM_FAULT_RETRY functionality can be
1793 *		utilised. Lock must initially be held.
1794 *
1795 * Returns either number of pages pinned (which may be less than the
1796 * number requested), or an error. Details about the return value:
1797 *
1798 * -- If nr_pages is 0, returns 0.
1799 * -- If nr_pages is >0, but no pages were pinned, returns -errno.
1800 * -- If nr_pages is >0, and some pages were pinned, returns the number of
1801 *    pages pinned. Again, this may be less than nr_pages.
1802 *
1803 * The caller is responsible for releasing returned @pages, via put_page().
1804 *
1805 * @vmas are valid only as long as mmap_lock is held.
1806 *
1807 * Must be called with mmap_lock held for read or write.
1808 *
1809 * get_user_pages_remote walks a process's page tables and takes a reference
1810 * to each struct page that each user address corresponds to at a given
1811 * instant. That is, it takes the page that would be accessed if a user
1812 * thread accesses the given user virtual address at that instant.
1813 *
1814 * This does not guarantee that the page exists in the user mappings when
1815 * get_user_pages_remote returns, and there may even be a completely different
1816 * page there in some cases (eg. if mmapped pagecache has been invalidated
1817 * and subsequently re faulted). However it does guarantee that the page
1818 * won't be freed completely. And mostly callers simply care that the page
1819 * contains data that was valid *at some point in time*. Typically, an IO
1820 * or similar operation cannot guarantee anything stronger anyway because
1821 * locks can't be held over the syscall boundary.
1822 *
1823 * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
1824 * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
1825 * be called after the page is finished with, and before put_page is called.
1826 *
1827 * get_user_pages_remote is typically used for fewer-copy IO operations,
1828 * to get a handle on the memory by some means other than accesses
1829 * via the user virtual addresses. The pages may be submitted for
1830 * DMA to devices or accessed via their kernel linear mapping (via the
1831 * kmap APIs). Care should be taken to use the correct cache flushing APIs.
1832 *
1833 * See also get_user_pages_fast, for performance critical applications.
1834 *
1835 * get_user_pages_remote should be phased out in favor of
1836 * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
1837 * should use get_user_pages_remote because it cannot pass
1838 * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
1839 */
1840long get_user_pages_remote(struct mm_struct *mm,
1841		unsigned long start, unsigned long nr_pages,
1842		unsigned int gup_flags, struct page **pages,
1843		struct vm_area_struct **vmas, int *locked)
1844{
1845	/*
1846	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
1847	 * never directly by the caller, so enforce that with an assertion:
1848	 */
1849	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
1850		return -EINVAL;
1851
1852	return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
1853				       pages, vmas, locked);
1854}
1855EXPORT_SYMBOL(get_user_pages_remote);
1856
1857#else /* CONFIG_MMU */
1858long get_user_pages_remote(struct mm_struct *mm,
1859			   unsigned long start, unsigned long nr_pages,
1860			   unsigned int gup_flags, struct page **pages,
1861			   struct vm_area_struct **vmas, int *locked)
1862{
1863	return 0;
1864}
1865
1866static long __get_user_pages_remote(struct mm_struct *mm,
1867				    unsigned long start, unsigned long nr_pages,
1868				    unsigned int gup_flags, struct page **pages,
1869				    struct vm_area_struct **vmas, int *locked)
1870{
1871	return 0;
1872}
1873#endif /* !CONFIG_MMU */
1874
1875/**
1876 * get_user_pages() - pin user pages in memory
1877 * @start:      starting user address
1878 * @nr_pages:   number of pages from start to pin
1879 * @gup_flags:  flags modifying lookup behaviour
1880 * @pages:      array that receives pointers to the pages pinned.
1881 *              Should be at least nr_pages long. Or NULL, if caller
1882 *              only intends to ensure the pages are faulted in.
1883 * @vmas:       array of pointers to vmas corresponding to each page.
1884 *              Or NULL if the caller does not require them.
1885 *
1886 * This is the same as get_user_pages_remote(), just with a less-flexible
1887 * calling convention where we assume that the mm being operated on belongs to
1888 * the current task, and doesn't allow passing of a locked parameter.  We also
1889 * obviously don't pass FOLL_REMOTE in here.
1890 */
1891long get_user_pages(unsigned long start, unsigned long nr_pages,
1892		unsigned int gup_flags, struct page **pages,
1893		struct vm_area_struct **vmas)
1894{
1895	/*
1896	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
1897	 * never directly by the caller, so enforce that with an assertion:
1898	 */
1899	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
1900		return -EINVAL;
1901
1902	return __gup_longterm_locked(current->mm, start, nr_pages,
1903				     pages, vmas, gup_flags | FOLL_TOUCH);
1904}
1905EXPORT_SYMBOL(get_user_pages);
1906
1907/**
1908 * get_user_pages_locked() is suitable to replace the form:
1909 *
1910 *      mmap_read_lock(mm);
1911 *      do_something()
1912 *      get_user_pages(mm, ..., pages, NULL);
1913 *      mmap_read_unlock(mm);
1914 *
1915 *  to:
1916 *
1917 *      int locked = 1;
1918 *      mmap_read_lock(mm);
1919 *      do_something()
1920 *      get_user_pages_locked(mm, ..., pages, &locked);
1921 *      if (locked)
1922 *          mmap_read_unlock(mm);
1923 *
1924 * @start:      starting user address
1925 * @nr_pages:   number of pages from start to pin
1926 * @gup_flags:  flags modifying lookup behaviour
1927 * @pages:      array that receives pointers to the pages pinned.
1928 *              Should be at least nr_pages long. Or NULL, if caller
1929 *              only intends to ensure the pages are faulted in.
1930 * @locked:     pointer to lock flag indicating whether lock is held and
1931 *              subsequently whether VM_FAULT_RETRY functionality can be
1932 *              utilised. Lock must initially be held.
1933 *
1934 * We can leverage the VM_FAULT_RETRY functionality in the page fault
1935 * paths better by using either get_user_pages_locked() or
1936 * get_user_pages_unlocked().
1937 *
1938 */
1939long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
1940			   unsigned int gup_flags, struct page **pages,
1941			   int *locked)
1942{
1943	/*
1944	 * FIXME: Current FOLL_LONGTERM behavior is incompatible with
1945	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
1946	 * vmas.  As there are no users of this flag in this call we simply
1947	 * disallow this option for now.
1948	 */
1949	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
1950		return -EINVAL;
1951	/*
1952	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
1953	 * never directly by the caller, so enforce that:
1954	 */
1955	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
1956		return -EINVAL;
1957
1958	return __get_user_pages_locked(current->mm, start, nr_pages,
1959				       pages, NULL, locked,
1960				       gup_flags | FOLL_TOUCH);
1961}
1962EXPORT_SYMBOL(get_user_pages_locked);
1963
1964/*
1965 * get_user_pages_unlocked() is suitable to replace the form:
1966 *
1967 *      mmap_read_lock(mm);
1968 *      get_user_pages(mm, ..., pages, NULL);
1969 *      mmap_read_unlock(mm);
1970 *
1971 *  with:
1972 *
1973 *      get_user_pages_unlocked(mm, ..., pages);
1974 *
1975 * It is functionally equivalent to get_user_pages_fast so
1976 * get_user_pages_fast should be used instead if specific gup_flags
1977 * (e.g. FOLL_FORCE) are not required.
1978 */
1979long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
1980			     struct page **pages, unsigned int gup_flags)
1981{
1982	struct mm_struct *mm = current->mm;
1983	int locked = 1;
1984	long ret;
1985
1986	/*
1987	 * FIXME: Current FOLL_LONGTERM behavior is incompatible with
1988	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
1989	 * vmas.  As there are no users of this flag in this call we simply
1990	 * disallow this option for now.
1991	 */
1992	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
1993		return -EINVAL;
1994
1995	mmap_read_lock(mm);
1996	ret = __get_user_pages_locked(mm, start, nr_pages, pages, NULL,
1997				      &locked, gup_flags | FOLL_TOUCH);
1998	if (locked)
1999		mmap_read_unlock(mm);
2000	return ret;
2001}
2002EXPORT_SYMBOL(get_user_pages_unlocked);
2003
2004/*
2005 * Fast GUP
2006 *
2007 * get_user_pages_fast attempts to pin user pages by walking the page
2008 * tables directly and avoids taking locks. Thus the walker needs to be
2009 * protected from page table pages being freed from under it, and should
2010 * block any THP splits.
2011 *
2012 * One way to achieve this is to have the walker disable interrupts, and
2013 * rely on IPIs from the TLB flushing code blocking before the page table
2014 * pages are freed. This is unsuitable for architectures that do not need
2015 * to broadcast an IPI when invalidating TLBs.
2016 *
2017 * Another way to achieve this is to batch up page table containing pages
2018 * belonging to more than one mm_user, then rcu_sched a callback to free those
2019 * pages. Disabling interrupts will allow the fast_gup walker to both block
2020 * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
2021 * (which is a relatively rare event). The code below adopts this strategy.
2022 *
2023 * Before activating this code, please be aware that the following assumptions
2024 * are currently made:
2025 *
2026 *  *) Either MMU_GATHER_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
2027 *  free pages containing page tables or TLB flushing requires IPI broadcast.
2028 *
2029 *  *) ptes can be read atomically by the architecture.
2030 *
2031 *  *) access_ok is sufficient to validate userspace address ranges.
2032 *
2033 * The last two assumptions can be relaxed by the addition of helper functions.
2034 *
2035 * This code is based heavily on the PowerPC implementation by Nick Piggin.
2036 */
2037#ifdef CONFIG_HAVE_FAST_GUP
2038
2039static void put_compound_head(struct page *page, int refs, unsigned int flags)
2040{
2041	if (flags & FOLL_PIN) {
2042		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
2043				    refs);
2044
2045		if (hpage_pincount_available(page))
2046			hpage_pincount_sub(page, refs);
2047		else
2048			refs *= GUP_PIN_COUNTING_BIAS;
2049	}
2050
2051	VM_BUG_ON_PAGE(page_ref_count(page) < refs, page);
2052	/*
2053	 * Calling put_page() for each ref is unnecessarily slow. Only the last
2054	 * ref needs a put_page().
2055	 */
2056	if (refs > 1)
2057		page_ref_sub(page, refs - 1);
2058	put_page(page);
2059}
2060
2061#ifdef CONFIG_GUP_GET_PTE_LOW_HIGH
2062
2063/*
2064 * WARNING: only to be used in the get_user_pages_fast() implementation.
2065 *
2066 * With get_user_pages_fast(), we walk down the pagetables without taking any
2067 * locks.  For this we would like to load the pointers atomically, but sometimes
2068 * that is not possible (e.g. without expensive cmpxchg8b on x86_32 PAE).  What
2069 * we do have is the guarantee that a PTE will only either go from not present
2070 * to present, or present to not present or both -- it will not switch to a
2071 * completely different present page without a TLB flush in between; something
2072 * that we are blocking by holding interrupts off.
2073 *
2074 * Setting ptes from not present to present goes:
2075 *
2076 *   ptep->pte_high = h;
2077 *   smp_wmb();
2078 *   ptep->pte_low = l;
2079 *
2080 * And present to not present goes:
2081 *
2082 *   ptep->pte_low = 0;
2083 *   smp_wmb();
2084 *   ptep->pte_high = 0;
2085 *
2086 * We must ensure here that the load of pte_low sees 'l' IFF pte_high sees 'h'.
2087 * We load pte_high *after* loading pte_low, which ensures we don't see an older
2088 * value of pte_high.  *Then* we recheck pte_low, which ensures that we haven't
2089 * picked up a changed pte high. We might have gotten rubbish values from
2090 * pte_low and pte_high, but we are guaranteed that pte_low will not have the
2091 * present bit set *unless* it is 'l'. Because get_user_pages_fast() only
2092 * operates on present ptes we're safe.
2093 */
2094static inline pte_t gup_get_pte(pte_t *ptep)
2095{
2096	pte_t pte;
2097
2098	do {
2099		pte.pte_low = ptep->pte_low;
2100		smp_rmb();
2101		pte.pte_high = ptep->pte_high;
2102		smp_rmb();
2103	} while (unlikely(pte.pte_low != ptep->pte_low));
2104
2105	return pte;
2106}
2107#else /* CONFIG_GUP_GET_PTE_LOW_HIGH */
2108/*
2109 * We require that the PTE can be read atomically.
2110 */
2111static inline pte_t gup_get_pte(pte_t *ptep)
2112{
2113	return ptep_get(ptep);
2114}
2115#endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */
2116
2117static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
2118					    unsigned int flags,
2119					    struct page **pages)
2120{
2121	while ((*nr) - nr_start) {
2122		struct page *page = pages[--(*nr)];
2123
2124		ClearPageReferenced(page);
2125		if (flags & FOLL_PIN)
2126			unpin_user_page(page);
2127		else
2128			put_page(page);
2129	}
2130}
2131
2132#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
2133static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
2134			 unsigned int flags, struct page **pages, int *nr)
2135{
2136	struct dev_pagemap *pgmap = NULL;
2137	int nr_start = *nr, ret = 0;
2138	pte_t *ptep, *ptem;
2139
2140	ptem = ptep = pte_offset_map(&pmd, addr);
2141	do {
2142		pte_t pte = gup_get_pte(ptep);
2143		struct page *head, *page;
2144
2145		/*
2146		 * Similar to the PMD case below, NUMA hinting must take slow
2147		 * path using the pte_protnone check.
2148		 */
2149		if (pte_protnone(pte))
2150			goto pte_unmap;
2151
2152		if (!pte_access_permitted(pte, flags & FOLL_WRITE))
2153			goto pte_unmap;
2154
2155		if (pte_devmap(pte)) {
2156			if (unlikely(flags & FOLL_LONGTERM))
2157				goto pte_unmap;
2158
2159			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
2160			if (unlikely(!pgmap)) {
2161				undo_dev_pagemap(nr, nr_start, flags, pages);
2162				goto pte_unmap;
2163			}
2164		} else if (pte_special(pte))
2165			goto pte_unmap;
2166
2167		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
2168		page = pte_page(pte);
2169
2170		head = try_grab_compound_head(page, 1, flags);
2171		if (!head)
2172			goto pte_unmap;
2173
2174		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
2175			put_compound_head(head, 1, flags);
2176			goto pte_unmap;
2177		}
2178
2179		VM_BUG_ON_PAGE(compound_head(page) != head, page);
2180
2181		/*
2182		 * We need to make the page accessible if and only if we are
2183		 * going to access its content (the FOLL_PIN case).  Please
2184		 * see Documentation/core-api/pin_user_pages.rst for
2185		 * details.
2186		 */
2187		if (flags & FOLL_PIN) {
2188			ret = arch_make_page_accessible(page);
2189			if (ret) {
2190				unpin_user_page(page);
2191				goto pte_unmap;
2192			}
2193		}
2194		SetPageReferenced(page);
2195		pages[*nr] = page;
2196		(*nr)++;
2197
2198	} while (ptep++, addr += PAGE_SIZE, addr != end);
2199
2200	ret = 1;
2201
2202pte_unmap:
2203	if (pgmap)
2204		put_dev_pagemap(pgmap);
2205	pte_unmap(ptem);
2206	return ret;
2207}
2208#else
2209
2210/*
2211 * If we can't determine whether or not a pte is special, then fail immediately
2212 * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
2213 * to be special.
2214 *
2215 * For a futex to be placed on a THP tail page, get_futex_key requires a
2216 * get_user_pages_fast_only implementation that can pin pages. Thus it's still
2217 * useful to have gup_huge_pmd even if we can't operate on ptes.
2218 */
2219static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
2220			 unsigned int flags, struct page **pages, int *nr)
2221{
2222	return 0;
2223}
2224#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
2225
2226#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
2227static int __gup_device_huge(unsigned long pfn, unsigned long addr,
2228			     unsigned long end, unsigned int flags,
2229			     struct page **pages, int *nr)
2230{
2231	int nr_start = *nr;
2232	struct dev_pagemap *pgmap = NULL;
2233
2234	do {
2235		struct page *page = pfn_to_page(pfn);
2236
2237		pgmap = get_dev_pagemap(pfn, pgmap);
2238		if (unlikely(!pgmap)) {
2239			undo_dev_pagemap(nr, nr_start, flags, pages);
2240			return 0;
2241		}
2242		SetPageReferenced(page);
2243		pages[*nr] = page;
2244		if (unlikely(!try_grab_page(page, flags))) {
2245			undo_dev_pagemap(nr, nr_start, flags, pages);
2246			return 0;
2247		}
2248		(*nr)++;
2249		pfn++;
2250	} while (addr += PAGE_SIZE, addr != end);
2251
2252	if (pgmap)
2253		put_dev_pagemap(pgmap);
2254	return 1;
2255}
2256
2257static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
2258				 unsigned long end, unsigned int flags,
2259				 struct page **pages, int *nr)
2260{
2261	unsigned long fault_pfn;
2262	int nr_start = *nr;
2263
2264	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
2265	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
2266		return 0;
2267
2268	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
2269		undo_dev_pagemap(nr, nr_start, flags, pages);
2270		return 0;
2271	}
2272	return 1;
2273}
2274
2275static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
2276				 unsigned long end, unsigned int flags,
2277				 struct page **pages, int *nr)
2278{
2279	unsigned long fault_pfn;
2280	int nr_start = *nr;
2281
2282	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
2283	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
2284		return 0;
2285
2286	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
2287		undo_dev_pagemap(nr, nr_start, flags, pages);
2288		return 0;
2289	}
2290	return 1;
2291}
2292#else
2293static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
2294				 unsigned long end, unsigned int flags,
2295				 struct page **pages, int *nr)
2296{
2297	BUILD_BUG();
2298	return 0;
2299}
2300
2301static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
2302				 unsigned long end, unsigned int flags,
2303				 struct page **pages, int *nr)
2304{
2305	BUILD_BUG();
2306	return 0;
2307}
2308#endif
2309
2310static int record_subpages(struct page *page, unsigned long addr,
2311			   unsigned long end, struct page **pages)
2312{
2313	int nr;
2314
2315	for (nr = 0; addr != end; addr += PAGE_SIZE)
2316		pages[nr++] = page++;
2317
2318	return nr;
2319}
2320
2321#ifdef CONFIG_ARCH_HAS_HUGEPD
2322static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
2323				      unsigned long sz)
2324{
2325	unsigned long __boundary = (addr + sz) & ~(sz-1);
2326	return (__boundary - 1 < end - 1) ? __boundary : end;
2327}
2328
2329static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
2330		       unsigned long end, unsigned int flags,
2331		       struct page **pages, int *nr)
2332{
2333	unsigned long pte_end;
2334	struct page *head, *page;
2335	pte_t pte;
2336	int refs;
2337
2338	pte_end = (addr + sz) & ~(sz-1);
2339	if (pte_end < end)
2340		end = pte_end;
2341
2342	pte = huge_ptep_get(ptep);
2343
2344	if (!pte_access_permitted(pte, flags & FOLL_WRITE))
2345		return 0;
2346
2347	/* hugepages are never "special" */
2348	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
2349
2350	head = pte_page(pte);
2351	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
2352	refs = record_subpages(page, addr, end, pages + *nr);
2353
2354	head = try_grab_compound_head(head, refs, flags);
2355	if (!head)
2356		return 0;
2357
2358	if (unlikely(pte_val(pte) != pte_val(*ptep))) {
2359		put_compound_head(head, refs, flags);
2360		return 0;
2361	}
2362
2363	*nr += refs;
2364	SetPageReferenced(head);
2365	return 1;
2366}
2367
2368static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
2369		unsigned int pdshift, unsigned long end, unsigned int flags,
2370		struct page **pages, int *nr)
2371{
2372	pte_t *ptep;
2373	unsigned long sz = 1UL << hugepd_shift(hugepd);
2374	unsigned long next;
2375
2376	ptep = hugepte_offset(hugepd, addr, pdshift);
2377	do {
2378		next = hugepte_addr_end(addr, end, sz);
2379		if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
2380			return 0;
2381	} while (ptep++, addr = next, addr != end);
2382
2383	return 1;
2384}
2385#else
2386static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
2387		unsigned int pdshift, unsigned long end, unsigned int flags,
2388		struct page **pages, int *nr)
2389{
2390	return 0;
2391}
2392#endif /* CONFIG_ARCH_HAS_HUGEPD */
2393
2394static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
2395			unsigned long end, unsigned int flags,
2396			struct page **pages, int *nr)
2397{
2398	struct page *head, *page;
2399	int refs;
2400
2401	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
2402		return 0;
2403
2404	if (pmd_devmap(orig)) {
2405		if (unlikely(flags & FOLL_LONGTERM))
2406			return 0;
2407		return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
2408					     pages, nr);
2409	}
2410
2411	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
2412	refs = record_subpages(page, addr, end, pages + *nr);
2413
2414	head = try_grab_compound_head(pmd_page(orig), refs, flags);
2415	if (!head)
2416		return 0;
2417
2418	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
2419		put_compound_head(head, refs, flags);
2420		return 0;
2421	}
2422
2423	*nr += refs;
2424	SetPageReferenced(head);
2425	return 1;
2426}
2427
2428static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
2429			unsigned long end, unsigned int flags,
2430			struct page **pages, int *nr)
2431{
2432	struct page *head, *page;
2433	int refs;
2434
2435	if (!pud_access_permitted(orig, flags & FOLL_WRITE))
2436		return 0;
2437
2438	if (pud_devmap(orig)) {
2439		if (unlikely(flags & FOLL_LONGTERM))
2440			return 0;
2441		return __gup_device_huge_pud(orig, pudp, addr, end, flags,
2442					     pages, nr);
2443	}
2444
2445	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
2446	refs = record_subpages(page, addr, end, pages + *nr);
2447
2448	head = try_grab_compound_head(pud_page(orig), refs, flags);
2449	if (!head)
2450		return 0;
2451
2452	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
2453		put_compound_head(head, refs, flags);
2454		return 0;
2455	}
2456
2457	*nr += refs;
2458	SetPageReferenced(head);
2459	return 1;
2460}
2461
2462static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
2463			unsigned long end, unsigned int flags,
2464			struct page **pages, int *nr)
2465{
2466	int refs;
2467	struct page *head, *page;
2468
2469	if (!pgd_access_permitted(orig, flags & FOLL_WRITE))
2470		return 0;
2471
2472	BUILD_BUG_ON(pgd_devmap(orig));
2473
2474	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
2475	refs = record_subpages(page, addr, end, pages + *nr);
2476
2477	head = try_grab_compound_head(pgd_page(orig), refs, flags);
2478	if (!head)
2479		return 0;
2480
2481	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
2482		put_compound_head(head, refs, flags);
2483		return 0;
2484	}
2485
2486	*nr += refs;
2487	SetPageReferenced(head);
2488	return 1;
2489}
2490
2491static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned long end,
2492		unsigned int flags, struct page **pages, int *nr)
2493{
2494	unsigned long next;
2495	pmd_t *pmdp;
2496
2497	pmdp = pmd_offset_lockless(pudp, pud, addr);
2498	do {
2499		pmd_t pmd = READ_ONCE(*pmdp);
2500
2501		next = pmd_addr_end(addr, end);
2502		if (!pmd_present(pmd))
2503			return 0;
2504
2505		if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
2506			     pmd_devmap(pmd))) {
2507			/*
2508			 * NUMA hinting faults need to be handled in the GUP
2509			 * slowpath for accounting purposes and so that they
2510			 * can be serialised against THP migration.
2511			 */
2512			if (pmd_protnone(pmd))
2513				return 0;
2514
2515			if (!gup_huge_pmd(pmd, pmdp, addr, next, flags,
2516				pages, nr))
2517				return 0;
2518
2519		} else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
2520			/*
2521			 * architecture have different format for hugetlbfs
2522			 * pmd format and THP pmd format
2523			 */
2524			if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
2525					 PMD_SHIFT, next, flags, pages, nr))
2526				return 0;
2527		} else if (!gup_pte_range(pmd, addr, next, flags, pages, nr))
2528			return 0;
2529	} while (pmdp++, addr = next, addr != end);
2530
2531	return 1;
2532}
2533
2534static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned long end,
2535			 unsigned int flags, struct page **pages, int *nr)
2536{
2537	unsigned long next;
2538	pud_t *pudp;
2539
2540	pudp = pud_offset_lockless(p4dp, p4d, addr);
2541	do {
2542		pud_t pud = READ_ONCE(*pudp);
2543
2544		next = pud_addr_end(addr, end);
2545		if (unlikely(!pud_present(pud)))
2546			return 0;
2547		if (unlikely(pud_huge(pud))) {
2548			if (!gup_huge_pud(pud, pudp, addr, next, flags,
2549					  pages, nr))
2550				return 0;
2551		} else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
2552			if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
2553					 PUD_SHIFT, next, flags, pages, nr))
2554				return 0;
2555		} else if (!gup_pmd_range(pudp, pud, addr, next, flags, pages, nr))
2556			return 0;
2557	} while (pudp++, addr = next, addr != end);
2558
2559	return 1;
2560}
2561
2562static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned long end,
2563			 unsigned int flags, struct page **pages, int *nr)
2564{
2565	unsigned long next;
2566	p4d_t *p4dp;
2567
2568	p4dp = p4d_offset_lockless(pgdp, pgd, addr);
2569	do {
2570		p4d_t p4d = READ_ONCE(*p4dp);
2571
2572		next = p4d_addr_end(addr, end);
2573		if (p4d_none(p4d))
2574			return 0;
2575		BUILD_BUG_ON(p4d_huge(p4d));
2576		if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
2577			if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
2578					 P4D_SHIFT, next, flags, pages, nr))
2579				return 0;
2580		} else if (!gup_pud_range(p4dp, p4d, addr, next, flags, pages, nr))
2581			return 0;
2582	} while (p4dp++, addr = next, addr != end);
2583
2584	return 1;
2585}
2586
2587static void gup_pgd_range(unsigned long addr, unsigned long end,
2588		unsigned int flags, struct page **pages, int *nr)
2589{
2590	unsigned long next;
2591	pgd_t *pgdp;
2592
2593	pgdp = pgd_offset(current->mm, addr);
2594	do {
2595		pgd_t pgd = READ_ONCE(*pgdp);
2596
2597		next = pgd_addr_end(addr, end);
2598		if (pgd_none(pgd))
2599			return;
2600		if (unlikely(pgd_huge(pgd))) {
2601			if (!gup_huge_pgd(pgd, pgdp, addr, next, flags,
2602					  pages, nr))
2603				return;
2604		} else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
2605			if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
2606					 PGDIR_SHIFT, next, flags, pages, nr))
2607				return;
2608		} else if (!gup_p4d_range(pgdp, pgd, addr, next, flags, pages, nr))
2609			return;
2610	} while (pgdp++, addr = next, addr != end);
2611}
2612#else
2613static inline void gup_pgd_range(unsigned long addr, unsigned long end,
2614		unsigned int flags, struct page **pages, int *nr)
2615{
2616}
2617#endif /* CONFIG_HAVE_FAST_GUP */
2618
2619#ifndef gup_fast_permitted
2620/*
2621 * Check if it's allowed to use get_user_pages_fast_only() for the range, or
2622 * we need to fall back to the slow version:
2623 */
2624static bool gup_fast_permitted(unsigned long start, unsigned long end)
2625{
2626	return true;
2627}
2628#endif
2629
2630static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
2631				   unsigned int gup_flags, struct page **pages)
2632{
2633	int ret;
2634
2635	/*
2636	 * FIXME: FOLL_LONGTERM does not work with
2637	 * get_user_pages_unlocked() (see comments in that function)
2638	 */
2639	if (gup_flags & FOLL_LONGTERM) {
2640		mmap_read_lock(current->mm);
2641		ret = __gup_longterm_locked(current->mm,
2642					    start, nr_pages,
2643					    pages, NULL, gup_flags);
2644		mmap_read_unlock(current->mm);
2645	} else {
2646		ret = get_user_pages_unlocked(start, nr_pages,
2647					      pages, gup_flags);
2648	}
2649
2650	return ret;
2651}
2652
2653static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
2654					unsigned int gup_flags,
2655					struct page **pages)
2656{
2657	unsigned long addr, len, end;
2658	unsigned long flags;
2659	int nr_pinned = 0, ret = 0;
2660
2661	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
2662				       FOLL_FORCE | FOLL_PIN | FOLL_GET |
2663				       FOLL_FAST_ONLY)))
2664		return -EINVAL;
2665
2666	if (gup_flags & FOLL_PIN)
2667		atomic_set(&current->mm->has_pinned, 1);
2668
2669	if (!(gup_flags & FOLL_FAST_ONLY))
2670		might_lock_read(&current->mm->mmap_lock);
2671
2672	start = untagged_addr(start) & PAGE_MASK;
2673	addr = start;
2674	len = (unsigned long) nr_pages << PAGE_SHIFT;
2675	end = start + len;
2676
2677	if (end <= start)
2678		return 0;
2679	if (unlikely(!access_ok((void __user *)start, len)))
2680		return -EFAULT;
2681
2682	/*
2683	 * Disable interrupts. The nested form is used, in order to allow
2684	 * full, general purpose use of this routine.
2685	 *
2686	 * With interrupts disabled, we block page table pages from being
2687	 * freed from under us. See struct mmu_table_batch comments in
2688	 * include/asm-generic/tlb.h for more details.
2689	 *
2690	 * We do not adopt an rcu_read_lock(.) here as we also want to
2691	 * block IPIs that come from THPs splitting.
2692	 */
2693	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) {
2694		unsigned long fast_flags = gup_flags;
2695
2696		local_irq_save(flags);
2697		gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned);
2698		local_irq_restore(flags);
2699		ret = nr_pinned;
2700	}
2701
2702	if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) {
2703		/* Try to get the remaining pages with get_user_pages */
2704		start += nr_pinned << PAGE_SHIFT;
2705		pages += nr_pinned;
2706
2707		ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned,
2708					      gup_flags, pages);
2709
2710		/* Have to be a bit careful with return values */
2711		if (nr_pinned > 0) {
2712			if (ret < 0)
2713				ret = nr_pinned;
2714			else
2715				ret += nr_pinned;
2716		}
2717	}
2718
2719	return ret;
2720}
2721/**
2722 * get_user_pages_fast_only() - pin user pages in memory
2723 * @start:      starting user address
2724 * @nr_pages:   number of pages from start to pin
2725 * @gup_flags:  flags modifying pin behaviour
2726 * @pages:      array that receives pointers to the pages pinned.
2727 *              Should be at least nr_pages long.
2728 *
2729 * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
2730 * the regular GUP.
2731 * Note a difference with get_user_pages_fast: this always returns the
2732 * number of pages pinned, 0 if no pages were pinned.
2733 *
2734 * If the architecture does not support this function, simply return with no
2735 * pages pinned.
2736 *
2737 * Careful, careful! COW breaking can go either way, so a non-write
2738 * access can get ambiguous page results. If you call this function without
2739 * 'write' set, you'd better be sure that you're ok with that ambiguity.
2740 */
2741int get_user_pages_fast_only(unsigned long start, int nr_pages,
2742			     unsigned int gup_flags, struct page **pages)
2743{
2744	int nr_pinned;
2745	/*
2746	 * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
2747	 * because gup fast is always a "pin with a +1 page refcount" request.
2748	 *
2749	 * FOLL_FAST_ONLY is required in order to match the API description of
2750	 * this routine: no fall back to regular ("slow") GUP.
2751	 */
2752	gup_flags |= FOLL_GET | FOLL_FAST_ONLY;
2753
2754	nr_pinned = internal_get_user_pages_fast(start, nr_pages, gup_flags,
2755						 pages);
2756
2757	/*
2758	 * As specified in the API description above, this routine is not
2759	 * allowed to return negative values. However, the common core
2760	 * routine internal_get_user_pages_fast() *can* return -errno.
2761	 * Therefore, correct for that here:
2762	 */
2763	if (nr_pinned < 0)
2764		nr_pinned = 0;
2765
2766	return nr_pinned;
2767}
2768EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
2769
2770/**
2771 * get_user_pages_fast() - pin user pages in memory
2772 * @start:      starting user address
2773 * @nr_pages:   number of pages from start to pin
2774 * @gup_flags:  flags modifying pin behaviour
2775 * @pages:      array that receives pointers to the pages pinned.
2776 *              Should be at least nr_pages long.
2777 *
2778 * Attempt to pin user pages in memory without taking mm->mmap_lock.
2779 * If not successful, it will fall back to taking the lock and
2780 * calling get_user_pages().
2781 *
2782 * Returns number of pages pinned. This may be fewer than the number requested.
2783 * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
2784 * -errno.
2785 */
2786int get_user_pages_fast(unsigned long start, int nr_pages,
2787			unsigned int gup_flags, struct page **pages)
2788{
2789	/*
2790	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
2791	 * never directly by the caller, so enforce that:
2792	 */
2793	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
2794		return -EINVAL;
2795
2796	/*
2797	 * The caller may or may not have explicitly set FOLL_GET; either way is
2798	 * OK. However, internally (within mm/gup.c), gup fast variants must set
2799	 * FOLL_GET, because gup fast is always a "pin with a +1 page refcount"
2800	 * request.
2801	 */
2802	gup_flags |= FOLL_GET;
2803	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
2804}
2805EXPORT_SYMBOL_GPL(get_user_pages_fast);
2806
2807/**
2808 * pin_user_pages_fast() - pin user pages in memory without taking locks
2809 *
2810 * @start:      starting user address
2811 * @nr_pages:   number of pages from start to pin
2812 * @gup_flags:  flags modifying pin behaviour
2813 * @pages:      array that receives pointers to the pages pinned.
2814 *              Should be at least nr_pages long.
2815 *
2816 * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
2817 * get_user_pages_fast() for documentation on the function arguments, because
2818 * the arguments here are identical.
2819 *
2820 * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
2821 * see Documentation/core-api/pin_user_pages.rst for further details.
2822 */
2823int pin_user_pages_fast(unsigned long start, int nr_pages,
2824			unsigned int gup_flags, struct page **pages)
2825{
2826	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
2827	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
2828		return -EINVAL;
2829
2830	gup_flags |= FOLL_PIN;
2831	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
2832}
2833EXPORT_SYMBOL_GPL(pin_user_pages_fast);
2834
2835/*
2836 * This is the FOLL_PIN equivalent of get_user_pages_fast_only(). Behavior
2837 * is the same, except that this one sets FOLL_PIN instead of FOLL_GET.
2838 *
2839 * The API rules are the same, too: no negative values may be returned.
2840 */
2841int pin_user_pages_fast_only(unsigned long start, int nr_pages,
2842			     unsigned int gup_flags, struct page **pages)
2843{
2844	int nr_pinned;
2845
2846	/*
2847	 * FOLL_GET and FOLL_PIN are mutually exclusive. Note that the API
2848	 * rules require returning 0, rather than -errno:
2849	 */
2850	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
2851		return 0;
2852	/*
2853	 * FOLL_FAST_ONLY is required in order to match the API description of
2854	 * this routine: no fall back to regular ("slow") GUP.
2855	 */
2856	gup_flags |= (FOLL_PIN | FOLL_FAST_ONLY);
2857	nr_pinned = internal_get_user_pages_fast(start, nr_pages, gup_flags,
2858						 pages);
2859	/*
2860	 * This routine is not allowed to return negative values. However,
2861	 * internal_get_user_pages_fast() *can* return -errno. Therefore,
2862	 * correct for that here:
2863	 */
2864	if (nr_pinned < 0)
2865		nr_pinned = 0;
2866
2867	return nr_pinned;
2868}
2869EXPORT_SYMBOL_GPL(pin_user_pages_fast_only);
2870
2871/**
2872 * pin_user_pages_remote() - pin pages of a remote process
2873 *
2874 * @mm:		mm_struct of target mm
2875 * @start:	starting user address
2876 * @nr_pages:	number of pages from start to pin
2877 * @gup_flags:	flags modifying lookup behaviour
2878 * @pages:	array that receives pointers to the pages pinned.
2879 *		Should be at least nr_pages long. Or NULL, if caller
2880 *		only intends to ensure the pages are faulted in.
2881 * @vmas:	array of pointers to vmas corresponding to each page.
2882 *		Or NULL if the caller does not require them.
2883 * @locked:	pointer to lock flag indicating whether lock is held and
2884 *		subsequently whether VM_FAULT_RETRY functionality can be
2885 *		utilised. Lock must initially be held.
2886 *
2887 * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See
2888 * get_user_pages_remote() for documentation on the function arguments, because
2889 * the arguments here are identical.
2890 *
2891 * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
2892 * see Documentation/core-api/pin_user_pages.rst for details.
2893 */
2894long pin_user_pages_remote(struct mm_struct *mm,
2895			   unsigned long start, unsigned long nr_pages,
2896			   unsigned int gup_flags, struct page **pages,
2897			   struct vm_area_struct **vmas, int *locked)
2898{
2899	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
2900	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
2901		return -EINVAL;
2902
2903	gup_flags |= FOLL_PIN;
2904	return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
2905				       pages, vmas, locked);
2906}
2907EXPORT_SYMBOL(pin_user_pages_remote);
2908
2909/**
2910 * pin_user_pages() - pin user pages in memory for use by other devices
2911 *
2912 * @start:	starting user address
2913 * @nr_pages:	number of pages from start to pin
2914 * @gup_flags:	flags modifying lookup behaviour
2915 * @pages:	array that receives pointers to the pages pinned.
2916 *		Should be at least nr_pages long. Or NULL, if caller
2917 *		only intends to ensure the pages are faulted in.
2918 * @vmas:	array of pointers to vmas corresponding to each page.
2919 *		Or NULL if the caller does not require them.
2920 *
2921 * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and
2922 * FOLL_PIN is set.
2923 *
2924 * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
2925 * see Documentation/core-api/pin_user_pages.rst for details.
2926 */
2927long pin_user_pages(unsigned long start, unsigned long nr_pages,
2928		    unsigned int gup_flags, struct page **pages,
2929		    struct vm_area_struct **vmas)
2930{
2931	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
2932	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
2933		return -EINVAL;
2934
2935	gup_flags |= FOLL_PIN;
2936	return __gup_longterm_locked(current->mm, start, nr_pages,
2937				     pages, vmas, gup_flags);
2938}
2939EXPORT_SYMBOL(pin_user_pages);
2940
2941/*
2942 * pin_user_pages_unlocked() is the FOLL_PIN variant of
2943 * get_user_pages_unlocked(). Behavior is the same, except that this one sets
2944 * FOLL_PIN and rejects FOLL_GET.
2945 */
2946long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
2947			     struct page **pages, unsigned int gup_flags)
2948{
2949	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
2950	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
2951		return -EINVAL;
2952
2953	gup_flags |= FOLL_PIN;
2954	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
2955}
2956EXPORT_SYMBOL(pin_user_pages_unlocked);
2957
2958/*
2959 * pin_user_pages_locked() is the FOLL_PIN variant of get_user_pages_locked().
2960 * Behavior is the same, except that this one sets FOLL_PIN and rejects
2961 * FOLL_GET.
2962 */
2963long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
2964			   unsigned int gup_flags, struct page **pages,
2965			   int *locked)
2966{
2967	/*
2968	 * FIXME: Current FOLL_LONGTERM behavior is incompatible with
2969	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
2970	 * vmas.  As there are no users of this flag in this call we simply
2971	 * disallow this option for now.
2972	 */
2973	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
2974		return -EINVAL;
2975
2976	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
2977	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
2978		return -EINVAL;
2979
2980	gup_flags |= FOLL_PIN;
2981	return __get_user_pages_locked(current->mm, start, nr_pages,
2982				       pages, NULL, locked,
2983				       gup_flags | FOLL_TOUCH);
2984}
2985EXPORT_SYMBOL(pin_user_pages_locked);