1#include <linux/kernel.h>
   2#include <linux/errno.h>
   3#include <linux/err.h>
   4#include <linux/spinlock.h>
   5
   6#include <linux/mm.h>
   7#include <linux/memremap.h>
   8#include <linux/pagemap.h>
   9#include <linux/rmap.h>
  10#include <linux/swap.h>
  11#include <linux/swapops.h>
  12
  13#include <linux/sched.h>
  14#include <linux/rwsem.h>
  15#include <linux/hugetlb.h>
  16
  17#include <asm/mmu_context.h>
  18#include <asm/pgtable.h>
  19#include <asm/tlbflush.h>
  20
  21#include "internal.h"
  22
  23static struct page *no_page_table(struct vm_area_struct *vma,
  24		unsigned int flags)
  25{
  26	/*
  27	 * When core dumping an enormous anonymous area that nobody
  28	 * has touched so far, we don't want to allocate unnecessary pages or
  29	 * page tables.  Return error instead of NULL to skip handle_mm_fault,
  30	 * then get_dump_page() will return NULL to leave a hole in the dump.
  31	 * But we can only make this optimization where a hole would surely
  32	 * be zero-filled if handle_mm_fault() actually did handle it.
  33	 */
  34	if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
  35		return ERR_PTR(-EFAULT);
  36	return NULL;
  37}
  38
  39static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
  40		pte_t *pte, unsigned int flags)
  41{
  42	/* No page to get reference */
  43	if (flags & FOLL_GET)
  44		return -EFAULT;
  45
  46	if (flags & FOLL_TOUCH) {
  47		pte_t entry = *pte;
  48
  49		if (flags & FOLL_WRITE)
  50			entry = pte_mkdirty(entry);
  51		entry = pte_mkyoung(entry);
  52
  53		if (!pte_same(*pte, entry)) {
  54			set_pte_at(vma->vm_mm, address, pte, entry);
  55			update_mmu_cache(vma, address, pte);
  56		}
  57	}
  58
  59	/* Proper page table entry exists, but no corresponding struct page */
  60	return -EEXIST;
  61}
  62
  63/*
  64 * FOLL_FORCE can write to even unwritable pte's, but only
  65 * after we've gone through a COW cycle and they are dirty.
  66 */
  67static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
  68{
  69	return pte_write(pte) ||
  70		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
  71}
  72
  73static struct page *follow_page_pte(struct vm_area_struct *vma,
  74		unsigned long address, pmd_t *pmd, unsigned int flags)
  75{
  76	struct mm_struct *mm = vma->vm_mm;
  77	struct dev_pagemap *pgmap = NULL;
  78	struct page *page;
  79	spinlock_t *ptl;
  80	pte_t *ptep, pte;
  81
  82retry:
  83	if (unlikely(pmd_bad(*pmd)))
  84		return no_page_table(vma, flags);
  85
  86	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
  87	pte = *ptep;
  88	if (!pte_present(pte)) {
  89		swp_entry_t entry;
  90		/*
  91		 * KSM's break_ksm() relies upon recognizing a ksm page
  92		 * even while it is being migrated, so for that case we
  93		 * need migration_entry_wait().
  94		 */
  95		if (likely(!(flags & FOLL_MIGRATION)))
  96			goto no_page;
  97		if (pte_none(pte))
  98			goto no_page;
  99		entry = pte_to_swp_entry(pte);
 100		if (!is_migration_entry(entry))
 101			goto no_page;
 102		pte_unmap_unlock(ptep, ptl);
 103		migration_entry_wait(mm, pmd, address);
 104		goto retry;
 105	}
 106	if ((flags & FOLL_NUMA) && pte_protnone(pte))
 107		goto no_page;
 108	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
 109		pte_unmap_unlock(ptep, ptl);
 110		return NULL;
 111	}
 112
 113	page = vm_normal_page(vma, address, pte);
 114	if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
 115		/*
 116		 * Only return device mapping pages in the FOLL_GET case since
 117		 * they are only valid while holding the pgmap reference.
 118		 */
 119		pgmap = get_dev_pagemap(pte_pfn(pte), NULL);
 120		if (pgmap)
 121			page = pte_page(pte);
 122		else
 123			goto no_page;
 124	} else if (unlikely(!page)) {
 125		if (flags & FOLL_DUMP) {
 126			/* Avoid special (like zero) pages in core dumps */
 127			page = ERR_PTR(-EFAULT);
 128			goto out;
 129		}
 130
 131		if (is_zero_pfn(pte_pfn(pte))) {
 132			page = pte_page(pte);
 133		} else {
 134			int ret;
 135
 136			ret = follow_pfn_pte(vma, address, ptep, flags);
 137			page = ERR_PTR(ret);
 138			goto out;
 139		}
 140	}
 141
 142	if (flags & FOLL_SPLIT && PageTransCompound(page)) {
 143		int ret;
 144		get_page(page);
 145		pte_unmap_unlock(ptep, ptl);
 146		lock_page(page);
 147		ret = split_huge_page(page);
 148		unlock_page(page);
 149		put_page(page);
 150		if (ret)
 151			return ERR_PTR(ret);
 152		goto retry;
 153	}
 154
 155	if (flags & FOLL_GET) {
 156		get_page(page);
 157
 158		/* drop the pgmap reference now that we hold the page */
 159		if (pgmap) {
 160			put_dev_pagemap(pgmap);
 161			pgmap = NULL;
 162		}
 163	}
 164	if (flags & FOLL_TOUCH) {
 165		if ((flags & FOLL_WRITE) &&
 166		    !pte_dirty(pte) && !PageDirty(page))
 167			set_page_dirty(page);
 168		/*
 169		 * pte_mkyoung() would be more correct here, but atomic care
 170		 * is needed to avoid losing the dirty bit: it is easier to use
 171		 * mark_page_accessed().
 172		 */
 173		mark_page_accessed(page);
 174	}
 175	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
 176		/* Do not mlock pte-mapped THP */
 177		if (PageTransCompound(page))
 178			goto out;
 179
 180		/*
 181		 * The preliminary mapping check is mainly to avoid the
 182		 * pointless overhead of lock_page on the ZERO_PAGE
 183		 * which might bounce very badly if there is contention.
 184		 *
 185		 * If the page is already locked, we don't need to
 186		 * handle it now - vmscan will handle it later if and
 187		 * when it attempts to reclaim the page.
 188		 */
 189		if (page->mapping && trylock_page(page)) {
 190			lru_add_drain();  /* push cached pages to LRU */
 191			/*
 192			 * Because we lock page here, and migration is
 193			 * blocked by the pte's page reference, and we
 194			 * know the page is still mapped, we don't even
 195			 * need to check for file-cache page truncation.
 196			 */
 197			mlock_vma_page(page);
 198			unlock_page(page);
 199		}
 200	}
 201out:
 202	pte_unmap_unlock(ptep, ptl);
 203	return page;
 204no_page:
 205	pte_unmap_unlock(ptep, ptl);
 206	if (!pte_none(pte))
 207		return NULL;
 208	return no_page_table(vma, flags);
 209}
 210
 211/**
 212 * follow_page_mask - look up a page descriptor from a user-virtual address
 213 * @vma: vm_area_struct mapping @address
 214 * @address: virtual address to look up
 215 * @flags: flags modifying lookup behaviour
 216 * @page_mask: on output, *page_mask is set according to the size of the page
 217 *
 218 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 219 *
 220 * Returns the mapped (struct page *), %NULL if no mapping exists, or
 221 * an error pointer if there is a mapping to something not represented
 222 * by a page descriptor (see also vm_normal_page()).
 223 */
 224struct page *follow_page_mask(struct vm_area_struct *vma,
 225			      unsigned long address, unsigned int flags,
 226			      unsigned int *page_mask)
 227{
 228	pgd_t *pgd;
 229	pud_t *pud;
 230	pmd_t *pmd;
 231	spinlock_t *ptl;
 232	struct page *page;
 233	struct mm_struct *mm = vma->vm_mm;
 234
 235	*page_mask = 0;
 236
 237	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
 238	if (!IS_ERR(page)) {
 239		BUG_ON(flags & FOLL_GET);
 240		return page;
 241	}
 242
 243	pgd = pgd_offset(mm, address);
 244	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
 245		return no_page_table(vma, flags);
 246
 247	pud = pud_offset(pgd, address);
 248	if (pud_none(*pud))
 249		return no_page_table(vma, flags);
 250	if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
 251		page = follow_huge_pud(mm, address, pud, flags);
 252		if (page)
 253			return page;
 254		return no_page_table(vma, flags);
 255	}
 256	if (unlikely(pud_bad(*pud)))
 257		return no_page_table(vma, flags);
 258
 259	pmd = pmd_offset(pud, address);
 260	if (pmd_none(*pmd))
 261		return no_page_table(vma, flags);
 262	if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
 263		page = follow_huge_pmd(mm, address, pmd, flags);
 264		if (page)
 265			return page;
 266		return no_page_table(vma, flags);
 267	}
 268	if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
 269		return no_page_table(vma, flags);
 270	if (pmd_devmap(*pmd)) {
 271		ptl = pmd_lock(mm, pmd);
 272		page = follow_devmap_pmd(vma, address, pmd, flags);
 273		spin_unlock(ptl);
 274		if (page)
 275			return page;
 276	}
 277	if (likely(!pmd_trans_huge(*pmd)))
 278		return follow_page_pte(vma, address, pmd, flags);
 279
 280	ptl = pmd_lock(mm, pmd);
 281	if (unlikely(!pmd_trans_huge(*pmd))) {
 282		spin_unlock(ptl);
 283		return follow_page_pte(vma, address, pmd, flags);
 284	}
 285	if (flags & FOLL_SPLIT) {
 286		int ret;
 287		page = pmd_page(*pmd);
 288		if (is_huge_zero_page(page)) {
 289			spin_unlock(ptl);
 290			ret = 0;
 291			split_huge_pmd(vma, pmd, address);
 292			if (pmd_trans_unstable(pmd))
 293				ret = -EBUSY;
 294		} else {
 295			get_page(page);
 296			spin_unlock(ptl);
 297			lock_page(page);
 298			ret = split_huge_page(page);
 299			unlock_page(page);
 300			put_page(page);
 301			if (pmd_none(*pmd))
 302				return no_page_table(vma, flags);
 303		}
 304
 305		return ret ? ERR_PTR(ret) :
 306			follow_page_pte(vma, address, pmd, flags);
 307	}
 308
 309	page = follow_trans_huge_pmd(vma, address, pmd, flags);
 310	spin_unlock(ptl);
 311	*page_mask = HPAGE_PMD_NR - 1;
 312	return page;
 313}
 314
 315static int get_gate_page(struct mm_struct *mm, unsigned long address,
 316		unsigned int gup_flags, struct vm_area_struct **vma,
 317		struct page **page)
 318{
 319	pgd_t *pgd;
 320	pud_t *pud;
 321	pmd_t *pmd;
 322	pte_t *pte;
 323	int ret = -EFAULT;
 324
 325	/* user gate pages are read-only */
 326	if (gup_flags & FOLL_WRITE)
 327		return -EFAULT;
 328	if (address > TASK_SIZE)
 329		pgd = pgd_offset_k(address);
 330	else
 331		pgd = pgd_offset_gate(mm, address);
 332	BUG_ON(pgd_none(*pgd));
 333	pud = pud_offset(pgd, address);
 334	BUG_ON(pud_none(*pud));
 335	pmd = pmd_offset(pud, address);
 336	if (pmd_none(*pmd))
 337		return -EFAULT;
 338	VM_BUG_ON(pmd_trans_huge(*pmd));
 339	pte = pte_offset_map(pmd, address);
 340	if (pte_none(*pte))
 341		goto unmap;
 342	*vma = get_gate_vma(mm);
 343	if (!page)
 344		goto out;
 345	*page = vm_normal_page(*vma, address, *pte);
 346	if (!*page) {
 347		if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
 348			goto unmap;
 349		*page = pte_page(*pte);
 350	}
 351	get_page(*page);
 352out:
 353	ret = 0;
 354unmap:
 355	pte_unmap(pte);
 356	return ret;
 357}
 358
 359/*
 360 * mmap_sem must be held on entry.  If @nonblocking != NULL and
 361 * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
 362 * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
 363 */
 364static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 365		unsigned long address, unsigned int *flags, int *nonblocking)
 366{
 367	unsigned int fault_flags = 0;
 368	int ret;
 369
 370	/* mlock all present pages, but do not fault in new pages */
 371	if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
 372		return -ENOENT;
 373	/* For mm_populate(), just skip the stack guard page. */
 374	if ((*flags & FOLL_POPULATE) &&
 375			(stack_guard_page_start(vma, address) ||
 376			 stack_guard_page_end(vma, address + PAGE_SIZE)))
 377		return -ENOENT;
 378	if (*flags & FOLL_WRITE)
 379		fault_flags |= FAULT_FLAG_WRITE;
 380	if (*flags & FOLL_REMOTE)
 381		fault_flags |= FAULT_FLAG_REMOTE;
 382	if (nonblocking)
 383		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 384	if (*flags & FOLL_NOWAIT)
 385		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 386	if (*flags & FOLL_TRIED) {
 387		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
 388		fault_flags |= FAULT_FLAG_TRIED;
 389	}
 390
 391	ret = handle_mm_fault(vma, address, fault_flags);
 392	if (ret & VM_FAULT_ERROR) {
 393		if (ret & VM_FAULT_OOM)
 394			return -ENOMEM;
 395		if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
 396			return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
 397		if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
 398			return -EFAULT;
 399		BUG();
 400	}
 401
 402	if (tsk) {
 403		if (ret & VM_FAULT_MAJOR)
 404			tsk->maj_flt++;
 405		else
 406			tsk->min_flt++;
 407	}
 408
 409	if (ret & VM_FAULT_RETRY) {
 410		if (nonblocking)
 411			*nonblocking = 0;
 412		return -EBUSY;
 413	}
 414
 415	/*
 416	 * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
 417	 * necessary, even if maybe_mkwrite decided not to set pte_write. We
 418	 * can thus safely do subsequent page lookups as if they were reads.
 419	 * But only do so when looping for pte_write is futile: in some cases
 420	 * userspace may also be wanting to write to the gotten user page,
 421	 * which a read fault here might prevent (a readonly page might get
 422	 * reCOWed by userspace write).
 423	 */
 424	if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
 425	        *flags |= FOLL_COW;
 426	return 0;
 427}
 428
 429static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 430{
 431	vm_flags_t vm_flags = vma->vm_flags;
 432	int write = (gup_flags & FOLL_WRITE);
 433	int foreign = (gup_flags & FOLL_REMOTE);
 434
 435	if (vm_flags & (VM_IO | VM_PFNMAP))
 436		return -EFAULT;
 437
 438	if (write) {
 439		if (!(vm_flags & VM_WRITE)) {
 440			if (!(gup_flags & FOLL_FORCE))
 441				return -EFAULT;
 442			/*
 443			 * We used to let the write,force case do COW in a
 444			 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
 445			 * set a breakpoint in a read-only mapping of an
 446			 * executable, without corrupting the file (yet only
 447			 * when that file had been opened for writing!).
 448			 * Anon pages in shared mappings are surprising: now
 449			 * just reject it.
 450			 */
 451			if (!is_cow_mapping(vm_flags))
 452				return -EFAULT;
 453		}
 454	} else if (!(vm_flags & VM_READ)) {
 455		if (!(gup_flags & FOLL_FORCE))
 456			return -EFAULT;
 457		/*
 458		 * Is there actually any vma we can reach here which does not
 459		 * have VM_MAYREAD set?
 460		 */
 461		if (!(vm_flags & VM_MAYREAD))
 462			return -EFAULT;
 463	}
 464	/*
 465	 * gups are always data accesses, not instruction
 466	 * fetches, so execute=false here
 467	 */
 468	if (!arch_vma_access_permitted(vma, write, false, foreign))
 469		return -EFAULT;
 470	return 0;
 471}
 472
 473/**
 474 * __get_user_pages() - pin user pages in memory
 475 * @tsk:	task_struct of target task
 476 * @mm:		mm_struct of target mm
 477 * @start:	starting user address
 478 * @nr_pages:	number of pages from start to pin
 479 * @gup_flags:	flags modifying pin behaviour
 480 * @pages:	array that receives pointers to the pages pinned.
 481 *		Should be at least nr_pages long. Or NULL, if caller
 482 *		only intends to ensure the pages are faulted in.
 483 * @vmas:	array of pointers to vmas corresponding to each page.
 484 *		Or NULL if the caller does not require them.
 485 * @nonblocking: whether waiting for disk IO or mmap_sem contention
 486 *
 487 * Returns number of pages pinned. This may be fewer than the number
 488 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 489 * were pinned, returns -errno. Each page returned must be released
 490 * with a put_page() call when it is finished with. vmas will only
 491 * remain valid while mmap_sem is held.
 492 *
 493 * Must be called with mmap_sem held.  It may be released.  See below.
 494 *
 495 * __get_user_pages walks a process's page tables and takes a reference to
 496 * each struct page that each user address corresponds to at a given
 497 * instant. That is, it takes the page that would be accessed if a user
 498 * thread accesses the given user virtual address at that instant.
 499 *
 500 * This does not guarantee that the page exists in the user mappings when
 501 * __get_user_pages returns, and there may even be a completely different
 502 * page there in some cases (eg. if mmapped pagecache has been invalidated
 503 * and subsequently re faulted). However it does guarantee that the page
 504 * won't be freed completely. And mostly callers simply care that the page
 505 * contains data that was valid *at some point in time*. Typically, an IO
 506 * or similar operation cannot guarantee anything stronger anyway because
 507 * locks can't be held over the syscall boundary.
 508 *
 509 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
 510 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
 511 * appropriate) must be called after the page is finished with, and
 512 * before put_page is called.
 513 *
 514 * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
 515 * or mmap_sem contention, and if waiting is needed to pin all pages,
 516 * *@nonblocking will be set to 0.  Further, if @gup_flags does not
 517 * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
 518 * this case.
 519 *
 520 * A caller using such a combination of @nonblocking and @gup_flags
 521 * must therefore hold the mmap_sem for reading only, and recognize
 522 * when it's been released.  Otherwise, it must be held for either
 523 * reading or writing and will not be released.
 524 *
 525 * In most cases, get_user_pages or get_user_pages_fast should be used
 526 * instead of __get_user_pages. __get_user_pages should be used only if
 527 * you need some special @gup_flags.
 528 */
 529static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 530		unsigned long start, unsigned long nr_pages,
 531		unsigned int gup_flags, struct page **pages,
 532		struct vm_area_struct **vmas, int *nonblocking)
 533{
 534	long i = 0;
 535	unsigned int page_mask;
 536	struct vm_area_struct *vma = NULL;
 537
 538	if (!nr_pages)
 539		return 0;
 540
 541	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
 542
 543	/*
 544	 * If FOLL_FORCE is set then do not force a full fault as the hinting
 545	 * fault information is unrelated to the reference behaviour of a task
 546	 * using the address space
 547	 */
 548	if (!(gup_flags & FOLL_FORCE))
 549		gup_flags |= FOLL_NUMA;
 550
 551	do {
 552		struct page *page;
 553		unsigned int foll_flags = gup_flags;
 554		unsigned int page_increm;
 555
 556		/* first iteration or cross vma bound */
 557		if (!vma || start >= vma->vm_end) {
 558			vma = find_extend_vma(mm, start);
 559			if (!vma && in_gate_area(mm, start)) {
 560				int ret;
 561				ret = get_gate_page(mm, start & PAGE_MASK,
 562						gup_flags, &vma,
 563						pages ? &pages[i] : NULL);
 564				if (ret)
 565					return i ? : ret;
 566				page_mask = 0;
 567				goto next_page;
 568			}
 569
 570			if (!vma || check_vma_flags(vma, gup_flags))
 571				return i ? : -EFAULT;
 572			if (is_vm_hugetlb_page(vma)) {
 573				i = follow_hugetlb_page(mm, vma, pages, vmas,
 574						&start, &nr_pages, i,
 575						gup_flags);
 576				continue;
 577			}
 578		}
 579retry:
 580		/*
 581		 * If we have a pending SIGKILL, don't keep faulting pages and
 582		 * potentially allocating memory.
 583		 */
 584		if (unlikely(fatal_signal_pending(current)))
 585			return i ? i : -ERESTARTSYS;
 586		cond_resched();
 587		page = follow_page_mask(vma, start, foll_flags, &page_mask);
 588		if (!page) {
 589			int ret;
 590			ret = faultin_page(tsk, vma, start, &foll_flags,
 591					nonblocking);
 592			switch (ret) {
 593			case 0:
 594				goto retry;
 595			case -EFAULT:
 596			case -ENOMEM:
 597			case -EHWPOISON:
 598				return i ? i : ret;
 599			case -EBUSY:
 600				return i;
 601			case -ENOENT:
 602				goto next_page;
 603			}
 604			BUG();
 605		} else if (PTR_ERR(page) == -EEXIST) {
 606			/*
 607			 * Proper page table entry exists, but no corresponding
 608			 * struct page.
 609			 */
 610			goto next_page;
 611		} else if (IS_ERR(page)) {
 612			return i ? i : PTR_ERR(page);
 613		}
 614		if (pages) {
 615			pages[i] = page;
 616			flush_anon_page(vma, page, start);
 617			flush_dcache_page(page);
 618			page_mask = 0;
 619		}
 620next_page:
 621		if (vmas) {
 622			vmas[i] = vma;
 623			page_mask = 0;
 624		}
 625		page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
 626		if (page_increm > nr_pages)
 627			page_increm = nr_pages;
 628		i += page_increm;
 629		start += page_increm * PAGE_SIZE;
 630		nr_pages -= page_increm;
 631	} while (nr_pages);
 632	return i;
 633}
 634
 635static bool vma_permits_fault(struct vm_area_struct *vma,
 636			      unsigned int fault_flags)
 637{
 638	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
 639	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
 640	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
 641
 642	if (!(vm_flags & vma->vm_flags))
 643		return false;
 644
 645	/*
 646	 * The architecture might have a hardware protection
 647	 * mechanism other than read/write that can deny access.
 648	 *
 649	 * gup always represents data access, not instruction
 650	 * fetches, so execute=false here:
 651	 */
 652	if (!arch_vma_access_permitted(vma, write, false, foreign))
 653		return false;
 654
 655	return true;
 656}
 657
 658/*
 659 * fixup_user_fault() - manually resolve a user page fault
 660 * @tsk:	the task_struct to use for page fault accounting, or
 661 *		NULL if faults are not to be recorded.
 662 * @mm:		mm_struct of target mm
 663 * @address:	user address
 664 * @fault_flags:flags to pass down to handle_mm_fault()
 665 * @unlocked:	did we unlock the mmap_sem while retrying, maybe NULL if caller
 666 *		does not allow retry
 667 *
 668 * This is meant to be called in the specific scenario where for locking reasons
 669 * we try to access user memory in atomic context (within a pagefault_disable()
 670 * section), this returns -EFAULT, and we want to resolve the user fault before
 671 * trying again.
 672 *
 673 * Typically this is meant to be used by the futex code.
 674 *
 675 * The main difference with get_user_pages() is that this function will
 676 * unconditionally call handle_mm_fault() which will in turn perform all the
 677 * necessary SW fixup of the dirty and young bits in the PTE, while
 678 * get_user_pages() only guarantees to update these in the struct page.
 679 *
 680 * This is important for some architectures where those bits also gate the
 681 * access permission to the page because they are maintained in software.  On
 682 * such architectures, gup() will not be enough to make a subsequent access
 683 * succeed.
 684 *
 685 * This function will not return with an unlocked mmap_sem. So it has not the
 686 * same semantics wrt the @mm->mmap_sem as does filemap_fault().
 687 */
 688int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 689		     unsigned long address, unsigned int fault_flags,
 690		     bool *unlocked)
 691{
 692	struct vm_area_struct *vma;
 693	int ret, major = 0;
 694
 695	if (unlocked)
 696		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 697
 698retry:
 699	vma = find_extend_vma(mm, address);
 700	if (!vma || address < vma->vm_start)
 701		return -EFAULT;
 702
 703	if (!vma_permits_fault(vma, fault_flags))
 704		return -EFAULT;
 705
 706	ret = handle_mm_fault(vma, address, fault_flags);
 707	major |= ret & VM_FAULT_MAJOR;
 708	if (ret & VM_FAULT_ERROR) {
 709		if (ret & VM_FAULT_OOM)
 710			return -ENOMEM;
 711		if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
 712			return -EHWPOISON;
 713		if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
 714			return -EFAULT;
 715		BUG();
 716	}
 717
 718	if (ret & VM_FAULT_RETRY) {
 719		down_read(&mm->mmap_sem);
 720		if (!(fault_flags & FAULT_FLAG_TRIED)) {
 721			*unlocked = true;
 722			fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
 723			fault_flags |= FAULT_FLAG_TRIED;
 724			goto retry;
 725		}
 726	}
 727
 728	if (tsk) {
 729		if (major)
 730			tsk->maj_flt++;
 731		else
 732			tsk->min_flt++;
 733	}
 734	return 0;
 735}
 736EXPORT_SYMBOL_GPL(fixup_user_fault);
 737
 738static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 739						struct mm_struct *mm,
 740						unsigned long start,
 741						unsigned long nr_pages,
 742						struct page **pages,
 743						struct vm_area_struct **vmas,
 744						int *locked, bool notify_drop,
 745						unsigned int flags)
 746{
 747	long ret, pages_done;
 748	bool lock_dropped;
 749
 750	if (locked) {
 751		/* if VM_FAULT_RETRY can be returned, vmas become invalid */
 752		BUG_ON(vmas);
 753		/* check caller initialized locked */
 754		BUG_ON(*locked != 1);
 755	}
 756
 757	if (pages)
 758		flags |= FOLL_GET;
 759
 760	pages_done = 0;
 761	lock_dropped = false;
 762	for (;;) {
 763		ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
 764				       vmas, locked);
 765		if (!locked)
 766			/* VM_FAULT_RETRY couldn't trigger, bypass */
 767			return ret;
 768
 769		/* VM_FAULT_RETRY cannot return errors */
 770		if (!*locked) {
 771			BUG_ON(ret < 0);
 772			BUG_ON(ret >= nr_pages);
 773		}
 774
 775		if (!pages)
 776			/* If it's a prefault don't insist harder */
 777			return ret;
 778
 779		if (ret > 0) {
 780			nr_pages -= ret;
 781			pages_done += ret;
 782			if (!nr_pages)
 783				break;
 784		}
 785		if (*locked) {
 786			/* VM_FAULT_RETRY didn't trigger */
 787			if (!pages_done)
 788				pages_done = ret;
 789			break;
 790		}
 791		/* VM_FAULT_RETRY triggered, so seek to the faulting offset */
 792		pages += ret;
 793		start += ret << PAGE_SHIFT;
 794
 795		/*
 796		 * Repeat on the address that fired VM_FAULT_RETRY
 797		 * without FAULT_FLAG_ALLOW_RETRY but with
 798		 * FAULT_FLAG_TRIED.
 799		 */
 800		*locked = 1;
 801		lock_dropped = true;
 802		down_read(&mm->mmap_sem);
 803		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
 804				       pages, NULL, NULL);
 805		if (ret != 1) {
 806			BUG_ON(ret > 1);
 807			if (!pages_done)
 808				pages_done = ret;
 809			break;
 810		}
 811		nr_pages--;
 812		pages_done++;
 813		if (!nr_pages)
 814			break;
 815		pages++;
 816		start += PAGE_SIZE;
 817	}
 818	if (notify_drop && lock_dropped && *locked) {
 819		/*
 820		 * We must let the caller know we temporarily dropped the lock
 821		 * and so the critical section protected by it was lost.
 822		 */
 823		up_read(&mm->mmap_sem);
 824		*locked = 0;
 825	}
 826	return pages_done;
 827}
 828
 829/*
 830 * We can leverage the VM_FAULT_RETRY functionality in the page fault
 831 * paths better by using either get_user_pages_locked() or
 832 * get_user_pages_unlocked().
 833 *
 834 * get_user_pages_locked() is suitable to replace the form:
 835 *
 836 *      down_read(&mm->mmap_sem);
 837 *      do_something()
 838 *      get_user_pages(tsk, mm, ..., pages, NULL);
 839 *      up_read(&mm->mmap_sem);
 840 *
 841 *  to:
 842 *
 843 *      int locked = 1;
 844 *      down_read(&mm->mmap_sem);
 845 *      do_something()
 846 *      get_user_pages_locked(tsk, mm, ..., pages, &locked);
 847 *      if (locked)
 848 *          up_read(&mm->mmap_sem);
 849 */
 850long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 851			   unsigned int gup_flags, struct page **pages,
 852			   int *locked)
 853{
 854	return __get_user_pages_locked(current, current->mm, start, nr_pages,
 855				       pages, NULL, locked, true,
 856				       gup_flags | FOLL_TOUCH);
 857}
 858EXPORT_SYMBOL(get_user_pages_locked);
 859
 860/*
 861 * Same as get_user_pages_unlocked(...., FOLL_TOUCH) but it allows for
 862 * tsk, mm to be specified.
 863 *
 864 * NOTE: here FOLL_TOUCH is not set implicitly and must be set by the
 865 * caller if required (just like with __get_user_pages). "FOLL_GET"
 866 * is set implicitly if "pages" is non-NULL.
 867 */
 868static __always_inline long __get_user_pages_unlocked(struct task_struct *tsk,
 869		struct mm_struct *mm, unsigned long start,
 870		unsigned long nr_pages, struct page **pages,
 871		unsigned int gup_flags)
 872{
 873	long ret;
 874	int locked = 1;
 875
 876	down_read(&mm->mmap_sem);
 877	ret = __get_user_pages_locked(tsk, mm, start, nr_pages, pages, NULL,
 878				      &locked, false, gup_flags);
 879	if (locked)
 880		up_read(&mm->mmap_sem);
 881	return ret;
 882}
 883
 884/*
 885 * get_user_pages_unlocked() is suitable to replace the form:
 886 *
 887 *      down_read(&mm->mmap_sem);
 888 *      get_user_pages(tsk, mm, ..., pages, NULL);
 889 *      up_read(&mm->mmap_sem);
 890 *
 891 *  with:
 892 *
 893 *      get_user_pages_unlocked(tsk, mm, ..., pages);
 894 *
 895 * It is functionally equivalent to get_user_pages_fast so
 896 * get_user_pages_fast should be used instead if specific gup_flags
 897 * (e.g. FOLL_FORCE) are not required.
 898 */
 899long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 900			     struct page **pages, unsigned int gup_flags)
 901{
 902	return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
 903					 pages, gup_flags | FOLL_TOUCH);
 904}
 905EXPORT_SYMBOL(get_user_pages_unlocked);
 906
 907/*
 908 * get_user_pages_remote() - pin user pages in memory
 909 * @tsk:	the task_struct to use for page fault accounting, or
 910 *		NULL if faults are not to be recorded.
 911 * @mm:		mm_struct of target mm
 912 * @start:	starting user address
 913 * @nr_pages:	number of pages from start to pin
 914 * @gup_flags:	flags modifying lookup behaviour
 915 * @pages:	array that receives pointers to the pages pinned.
 916 *		Should be at least nr_pages long. Or NULL, if caller
 917 *		only intends to ensure the pages are faulted in.
 918 * @vmas:	array of pointers to vmas corresponding to each page.
 919 *		Or NULL if the caller does not require them.
 920 * @locked:	pointer to lock flag indicating whether lock is held and
 921 *		subsequently whether VM_FAULT_RETRY functionality can be
 922 *		utilised. Lock must initially be held.
 923 *
 924 * Returns number of pages pinned. This may be fewer than the number
 925 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 926 * were pinned, returns -errno. Each page returned must be released
 927 * with a put_page() call when it is finished with. vmas will only
 928 * remain valid while mmap_sem is held.
 929 *
 930 * Must be called with mmap_sem held for read or write.
 931 *
 932 * get_user_pages walks a process's page tables and takes a reference to
 933 * each struct page that each user address corresponds to at a given
 934 * instant. That is, it takes the page that would be accessed if a user
 935 * thread accesses the given user virtual address at that instant.
 936 *
 937 * This does not guarantee that the page exists in the user mappings when
 938 * get_user_pages returns, and there may even be a completely different
 939 * page there in some cases (eg. if mmapped pagecache has been invalidated
 940 * and subsequently re faulted). However it does guarantee that the page
 941 * won't be freed completely. And mostly callers simply care that the page
 942 * contains data that was valid *at some point in time*. Typically, an IO
 943 * or similar operation cannot guarantee anything stronger anyway because
 944 * locks can't be held over the syscall boundary.
 945 *
 946 * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
 947 * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
 948 * be called after the page is finished with, and before put_page is called.
 949 *
 950 * get_user_pages is typically used for fewer-copy IO operations, to get a
 951 * handle on the memory by some means other than accesses via the user virtual
 952 * addresses. The pages may be submitted for DMA to devices or accessed via
 953 * their kernel linear mapping (via the kmap APIs). Care should be taken to
 954 * use the correct cache flushing APIs.
 955 *
 956 * See also get_user_pages_fast, for performance critical applications.
 957 *
 958 * get_user_pages should be phased out in favor of
 959 * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
 960 * should use get_user_pages because it cannot pass
 961 * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
 962 */
 963long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 964		unsigned long start, unsigned long nr_pages,
 965		unsigned int gup_flags, struct page **pages,
 966		struct vm_area_struct **vmas, int *locked)
 967{
 968	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
 969				       locked, true,
 970				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
 971}
 972EXPORT_SYMBOL(get_user_pages_remote);
 973
 974/*
 975 * This is the same as get_user_pages_remote(), just with a
 976 * less-flexible calling convention where we assume that the task
 977 * and mm being operated on are the current task's and don't allow
 978 * passing of a locked parameter.  We also obviously don't pass
 979 * FOLL_REMOTE in here.
 980 */
 981long get_user_pages(unsigned long start, unsigned long nr_pages,
 982		unsigned int gup_flags, struct page **pages,
 983		struct vm_area_struct **vmas)
 984{
 985	return __get_user_pages_locked(current, current->mm, start, nr_pages,
 986				       pages, vmas, NULL, false,
 987				       gup_flags | FOLL_TOUCH);
 988}
 989EXPORT_SYMBOL(get_user_pages);
 990
 991/**
 992 * populate_vma_page_range() -  populate a range of pages in the vma.
 993 * @vma:   target vma
 994 * @start: start address
 995 * @end:   end address
 996 * @nonblocking:
 997 *
 998 * This takes care of mlocking the pages too if VM_LOCKED is set.
 999 *
1000 * return 0 on success, negative error code on error.
1001 *
1002 * vma->vm_mm->mmap_sem must be held.
1003 *
1004 * If @nonblocking is NULL, it may be held for read or write and will
1005 * be unperturbed.
1006 *
1007 * If @nonblocking is non-NULL, it must held for read only and may be
1008 * released.  If it's released, *@nonblocking will be set to 0.
1009 */
1010long populate_vma_page_range(struct vm_area_struct *vma,
1011		unsigned long start, unsigned long end, int *nonblocking)
1012{
1013	struct mm_struct *mm = vma->vm_mm;
1014	unsigned long nr_pages = (end - start) / PAGE_SIZE;
1015	int gup_flags;
1016
1017	VM_BUG_ON(start & ~PAGE_MASK);
1018	VM_BUG_ON(end   & ~PAGE_MASK);
1019	VM_BUG_ON_VMA(start < vma->vm_start, vma);
1020	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
1021	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
1022
1023	gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
1024	if (vma->vm_flags & VM_LOCKONFAULT)
1025		gup_flags &= ~FOLL_POPULATE;
1026	/*
1027	 * We want to touch writable mappings with a write fault in order
1028	 * to break COW, except for shared mappings because these don't COW
1029	 * and we would not want to dirty them for nothing.
1030	 */
1031	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
1032		gup_flags |= FOLL_WRITE;
1033
1034	/*
1035	 * We want mlock to succeed for regions that have any permissions
1036	 * other than PROT_NONE.
1037	 */
1038	if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
1039		gup_flags |= FOLL_FORCE;
1040
1041	/*
1042	 * We made sure addr is within a VMA, so the following will
1043	 * not result in a stack expansion that recurses back here.
1044	 */
1045	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
1046				NULL, NULL, nonblocking);
1047}
1048
1049/*
1050 * __mm_populate - populate and/or mlock pages within a range of address space.
1051 *
1052 * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
1053 * flags. VMAs must be already marked with the desired vm_flags, and
1054 * mmap_sem must not be held.
1055 */
1056int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
1057{
1058	struct mm_struct *mm = current->mm;
1059	unsigned long end, nstart, nend;
1060	struct vm_area_struct *vma = NULL;
1061	int locked = 0;
1062	long ret = 0;
1063
1064	VM_BUG_ON(start & ~PAGE_MASK);
1065	VM_BUG_ON(len != PAGE_ALIGN(len));
1066	end = start + len;
1067
1068	for (nstart = start; nstart < end; nstart = nend) {
1069		/*
1070		 * We want to fault in pages for [nstart; end) address range.
1071		 * Find first corresponding VMA.
1072		 */
1073		if (!locked) {
1074			locked = 1;
1075			down_read(&mm->mmap_sem);
1076			vma = find_vma(mm, nstart);
1077		} else if (nstart >= vma->vm_end)
1078			vma = vma->vm_next;
1079		if (!vma || vma->vm_start >= end)
1080			break;
1081		/*
1082		 * Set [nstart; nend) to intersection of desired address
1083		 * range with the first VMA. Also, skip undesirable VMA types.
1084		 */
1085		nend = min(end, vma->vm_end);
1086		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
1087			continue;
1088		if (nstart < vma->vm_start)
1089			nstart = vma->vm_start;
1090		/*
1091		 * Now fault in a range of pages. populate_vma_page_range()
1092		 * double checks the vma flags, so that it won't mlock pages
1093		 * if the vma was already munlocked.
1094		 */
1095		ret = populate_vma_page_range(vma, nstart, nend, &locked);
1096		if (ret < 0) {
1097			if (ignore_errors) {
1098				ret = 0;
1099				continue;	/* continue at next VMA */
1100			}
1101			break;
1102		}
1103		nend = nstart + ret * PAGE_SIZE;
1104		ret = 0;
1105	}
1106	if (locked)
1107		up_read(&mm->mmap_sem);
1108	return ret;	/* 0 or negative error code */
1109}
1110
1111/**
1112 * get_dump_page() - pin user page in memory while writing it to core dump
1113 * @addr: user address
1114 *
1115 * Returns struct page pointer of user page pinned for dump,
1116 * to be freed afterwards by put_page().
1117 *
1118 * Returns NULL on any kind of failure - a hole must then be inserted into
1119 * the corefile, to preserve alignment with its headers; and also returns
1120 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
1121 * allowing a hole to be left in the corefile to save diskspace.
1122 *
1123 * Called without mmap_sem, but after all other threads have been killed.
1124 */
1125#ifdef CONFIG_ELF_CORE
1126struct page *get_dump_page(unsigned long addr)
1127{
1128	struct vm_area_struct *vma;
1129	struct page *page;
1130
1131	if (__get_user_pages(current, current->mm, addr, 1,
1132			     FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
1133			     NULL) < 1)
1134		return NULL;
1135	flush_cache_page(vma, addr, page_to_pfn(page));
1136	return page;
1137}
1138#endif /* CONFIG_ELF_CORE */
1139
1140/*
1141 * Generic RCU Fast GUP
1142 *
1143 * get_user_pages_fast attempts to pin user pages by walking the page
1144 * tables directly and avoids taking locks. Thus the walker needs to be
1145 * protected from page table pages being freed from under it, and should
1146 * block any THP splits.
1147 *
1148 * One way to achieve this is to have the walker disable interrupts, and
1149 * rely on IPIs from the TLB flushing code blocking before the page table
1150 * pages are freed. This is unsuitable for architectures that do not need
1151 * to broadcast an IPI when invalidating TLBs.
1152 *
1153 * Another way to achieve this is to batch up page table containing pages
1154 * belonging to more than one mm_user, then rcu_sched a callback to free those
1155 * pages. Disabling interrupts will allow the fast_gup walker to both block
1156 * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
1157 * (which is a relatively rare event). The code below adopts this strategy.
1158 *
1159 * Before activating this code, please be aware that the following assumptions
1160 * are currently made:
1161 *
1162 *  *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
1163 *      pages containing page tables.
1164 *
1165 *  *) ptes can be read atomically by the architecture.
1166 *
1167 *  *) access_ok is sufficient to validate userspace address ranges.
1168 *
1169 * The last two assumptions can be relaxed by the addition of helper functions.
1170 *
1171 * This code is based heavily on the PowerPC implementation by Nick Piggin.
1172 */
1173#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
1174
1175#ifdef __HAVE_ARCH_PTE_SPECIAL
1176static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
1177			 int write, struct page **pages, int *nr)
1178{
1179	pte_t *ptep, *ptem;
1180	int ret = 0;
1181
1182	ptem = ptep = pte_offset_map(&pmd, addr);
1183	do {
1184		/*
1185		 * In the line below we are assuming that the pte can be read
1186		 * atomically. If this is not the case for your architecture,
1187		 * please wrap this in a helper function!
1188		 *
1189		 * for an example see gup_get_pte in arch/x86/mm/gup.c
1190		 */
1191		pte_t pte = READ_ONCE(*ptep);
1192		struct page *head, *page;
1193
1194		/*
1195		 * Similar to the PMD case below, NUMA hinting must take slow
1196		 * path using the pte_protnone check.
1197		 */
1198		if (!pte_present(pte) || pte_special(pte) ||
1199			pte_protnone(pte) || (write && !pte_write(pte)))
1200			goto pte_unmap;
1201
1202		if (!arch_pte_access_permitted(pte, write))
1203			goto pte_unmap;
1204
1205		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
1206		page = pte_page(pte);
1207		head = compound_head(page);
1208
1209		if (!page_cache_get_speculative(head))
1210			goto pte_unmap;
1211
1212		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
1213			put_page(head);
1214			goto pte_unmap;
1215		}
1216
1217		VM_BUG_ON_PAGE(compound_head(page) != head, page);
1218		pages[*nr] = page;
1219		(*nr)++;
1220
1221	} while (ptep++, addr += PAGE_SIZE, addr != end);
1222
1223	ret = 1;
1224
1225pte_unmap:
1226	pte_unmap(ptem);
1227	return ret;
1228}
1229#else
1230
1231/*
1232 * If we can't determine whether or not a pte is special, then fail immediately
1233 * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
1234 * to be special.
1235 *
1236 * For a futex to be placed on a THP tail page, get_futex_key requires a
1237 * __get_user_pages_fast implementation that can pin pages. Thus it's still
1238 * useful to have gup_huge_pmd even if we can't operate on ptes.
1239 */
1240static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
1241			 int write, struct page **pages, int *nr)
1242{
1243	return 0;
1244}
1245#endif /* __HAVE_ARCH_PTE_SPECIAL */
1246
1247static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1248		unsigned long end, int write, struct page **pages, int *nr)
1249{
1250	struct page *head, *page;
1251	int refs;
1252
1253	if (write && !pmd_write(orig))
1254		return 0;
1255
1256	refs = 0;
1257	head = pmd_page(orig);
1258	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
1259	do {
1260		VM_BUG_ON_PAGE(compound_head(page) != head, page);
1261		pages[*nr] = page;
1262		(*nr)++;
1263		page++;
1264		refs++;
1265	} while (addr += PAGE_SIZE, addr != end);
1266
1267	if (!page_cache_add_speculative(head, refs)) {
1268		*nr -= refs;
1269		return 0;
1270	}
1271
1272	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
1273		*nr -= refs;
1274		while (refs--)
1275			put_page(head);
1276		return 0;
1277	}
1278
1279	return 1;
1280}
1281
1282static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
1283		unsigned long end, int write, struct page **pages, int *nr)
1284{
1285	struct page *head, *page;
1286	int refs;
1287
1288	if (write && !pud_write(orig))
1289		return 0;
1290
1291	refs = 0;
1292	head = pud_page(orig);
1293	page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
1294	do {
1295		VM_BUG_ON_PAGE(compound_head(page) != head, page);
1296		pages[*nr] = page;
1297		(*nr)++;
1298		page++;
1299		refs++;
1300	} while (addr += PAGE_SIZE, addr != end);
1301
1302	if (!page_cache_add_speculative(head, refs)) {
1303		*nr -= refs;
1304		return 0;
1305	}
1306
1307	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
1308		*nr -= refs;
1309		while (refs--)
1310			put_page(head);
1311		return 0;
1312	}
1313
1314	return 1;
1315}
1316
1317static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
1318			unsigned long end, int write,
1319			struct page **pages, int *nr)
1320{
1321	int refs;
1322	struct page *head, *page;
1323
1324	if (write && !pgd_write(orig))
1325		return 0;
1326
1327	refs = 0;
1328	head = pgd_page(orig);
1329	page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
1330	do {
1331		VM_BUG_ON_PAGE(compound_head(page) != head, page);
1332		pages[*nr] = page;
1333		(*nr)++;
1334		page++;
1335		refs++;
1336	} while (addr += PAGE_SIZE, addr != end);
1337
1338	if (!page_cache_add_speculative(head, refs)) {
1339		*nr -= refs;
1340		return 0;
1341	}
1342
1343	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
1344		*nr -= refs;
1345		while (refs--)
1346			put_page(head);
1347		return 0;
1348	}
1349
1350	return 1;
1351}
1352
1353static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
1354		int write, struct page **pages, int *nr)
1355{
1356	unsigned long next;
1357	pmd_t *pmdp;
1358
1359	pmdp = pmd_offset(&pud, addr);
1360	do {
1361		pmd_t pmd = READ_ONCE(*pmdp);
1362
1363		next = pmd_addr_end(addr, end);
1364		if (pmd_none(pmd))
1365			return 0;
1366
1367		if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) {
1368			/*
1369			 * NUMA hinting faults need to be handled in the GUP
1370			 * slowpath for accounting purposes and so that they
1371			 * can be serialised against THP migration.
1372			 */
1373			if (pmd_protnone(pmd))
1374				return 0;
1375
1376			if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
1377				pages, nr))
1378				return 0;
1379
1380		} else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
1381			/*
1382			 * architecture have different format for hugetlbfs
1383			 * pmd format and THP pmd format
1384			 */
1385			if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
1386					 PMD_SHIFT, next, write, pages, nr))
1387				return 0;
1388		} else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
1389				return 0;
1390	} while (pmdp++, addr = next, addr != end);
1391
1392	return 1;
1393}
1394
1395static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
1396			 int write, struct page **pages, int *nr)
1397{
1398	unsigned long next;
1399	pud_t *pudp;
1400
1401	pudp = pud_offset(&pgd, addr);
1402	do {
1403		pud_t pud = READ_ONCE(*pudp);
1404
1405		next = pud_addr_end(addr, end);
1406		if (pud_none(pud))
1407			return 0;
1408		if (unlikely(pud_huge(pud))) {
1409			if (!gup_huge_pud(pud, pudp, addr, next, write,
1410					  pages, nr))
1411				return 0;
1412		} else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
1413			if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
1414					 PUD_SHIFT, next, write, pages, nr))
1415				return 0;
1416		} else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
1417			return 0;
1418	} while (pudp++, addr = next, addr != end);
1419
1420	return 1;
1421}
1422
1423/*
1424 * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
1425 * the regular GUP. It will only return non-negative values.
1426 */
1427int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
1428			  struct page **pages)
1429{
1430	struct mm_struct *mm = current->mm;
1431	unsigned long addr, len, end;
1432	unsigned long next, flags;
1433	pgd_t *pgdp;
1434	int nr = 0;
1435
1436	start &= PAGE_MASK;
1437	addr = start;
1438	len = (unsigned long) nr_pages << PAGE_SHIFT;
1439	end = start + len;
1440
1441	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
1442					start, len)))
1443		return 0;
1444
1445	/*
1446	 * Disable interrupts.  We use the nested form as we can already have
1447	 * interrupts disabled by get_futex_key.
1448	 *
1449	 * With interrupts disabled, we block page table pages from being
1450	 * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
1451	 * for more details.
1452	 *
1453	 * We do not adopt an rcu_read_lock(.) here as we also want to
1454	 * block IPIs that come from THPs splitting.
1455	 */
1456
1457	local_irq_save(flags);
1458	pgdp = pgd_offset(mm, addr);
1459	do {
1460		pgd_t pgd = READ_ONCE(*pgdp);
1461
1462		next = pgd_addr_end(addr, end);
1463		if (pgd_none(pgd))
1464			break;
1465		if (unlikely(pgd_huge(pgd))) {
1466			if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
1467					  pages, &nr))
1468				break;
1469		} else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
1470			if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
1471					 PGDIR_SHIFT, next, write, pages, &nr))
1472				break;
1473		} else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
1474			break;
1475	} while (pgdp++, addr = next, addr != end);
1476	local_irq_restore(flags);
1477
1478	return nr;
1479}
1480
1481/**
1482 * get_user_pages_fast() - pin user pages in memory
1483 * @start:	starting user address
1484 * @nr_pages:	number of pages from start to pin
1485 * @write:	whether pages will be written to
1486 * @pages:	array that receives pointers to the pages pinned.
1487 *		Should be at least nr_pages long.
1488 *
1489 * Attempt to pin user pages in memory without taking mm->mmap_sem.
1490 * If not successful, it will fall back to taking the lock and
1491 * calling get_user_pages().
1492 *
1493 * Returns number of pages pinned. This may be fewer than the number
1494 * requested. If nr_pages is 0 or negative, returns 0. If no pages
1495 * were pinned, returns -errno.
1496 */
1497int get_user_pages_fast(unsigned long start, int nr_pages, int write,
1498			struct page **pages)
1499{
1500	int nr, ret;
1501
1502	start &= PAGE_MASK;
1503	nr = __get_user_pages_fast(start, nr_pages, write, pages);
1504	ret = nr;
1505
1506	if (nr < nr_pages) {
1507		/* Try to get the remaining pages with get_user_pages */
1508		start += nr << PAGE_SHIFT;
1509		pages += nr;
1510
1511		ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
1512				write ? FOLL_WRITE : 0);
1513
1514		/* Have to be a bit careful with return values */
1515		if (nr > 0) {
1516			if (ret < 0)
1517				ret = nr;
1518			else
1519				ret += nr;
1520		}
1521	}
1522
1523	return ret;
1524}
1525
1526#endif /* CONFIG_HAVE_GENERIC_RCU_GUP */