gup.c 65.5 KB
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// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/spinlock.h>

#include <linux/mm.h>
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#include <linux/memremap.h>
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#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>

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#include <linux/sched/signal.h>
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#include <linux/rwsem.h>
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#include <linux/hugetlb.h>
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#include <linux/migrate.h>
#include <linux/mm_inline.h>
#include <linux/sched/mm.h>
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#include <asm/mmu_context.h>
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#include <asm/pgtable.h>
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#include <asm/tlbflush.h>
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#include "internal.h"

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struct follow_page_context {
	struct dev_pagemap *pgmap;
	unsigned int page_mask;
};

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/**
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 * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
 * @pages:  array of pages to be maybe marked dirty, and definitely released.
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 * @npages: number of pages in the @pages array.
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 * @make_dirty: whether to mark the pages dirty
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 *
 * "gup-pinned page" refers to a page that has had one of the get_user_pages()
 * variants called on that page.
 *
 * For each page in the @pages array, make that page (or its head page, if a
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 * compound page) dirty, if @make_dirty is true, and if the page was previously
 * listed as clean. In any case, releases all pages using put_user_page(),
 * possibly via put_user_pages(), for the non-dirty case.
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 *
 * Please see the put_user_page() documentation for details.
 *
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 * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
 * required, then the caller should a) verify that this is really correct,
 * because _lock() is usually required, and b) hand code it:
 * set_page_dirty_lock(), put_user_page().
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 *
 */
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void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
			       bool make_dirty)
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{
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	unsigned long index;
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	/*
	 * TODO: this can be optimized for huge pages: if a series of pages is
	 * physically contiguous and part of the same compound page, then a
	 * single operation to the head page should suffice.
	 */

	if (!make_dirty) {
		put_user_pages(pages, npages);
		return;
	}

	for (index = 0; index < npages; index++) {
		struct page *page = compound_head(pages[index]);
		/*
		 * Checking PageDirty at this point may race with
		 * clear_page_dirty_for_io(), but that's OK. Two key
		 * cases:
		 *
		 * 1) This code sees the page as already dirty, so it
		 * skips the call to set_page_dirty(). That could happen
		 * because clear_page_dirty_for_io() called
		 * page_mkclean(), followed by set_page_dirty().
		 * However, now the page is going to get written back,
		 * which meets the original intention of setting it
		 * dirty, so all is well: clear_page_dirty_for_io() goes
		 * on to call TestClearPageDirty(), and write the page
		 * back.
		 *
		 * 2) This code sees the page as clean, so it calls
		 * set_page_dirty(). The page stays dirty, despite being
		 * written back, so it gets written back again in the
		 * next writeback cycle. This is harmless.
		 */
		if (!PageDirty(page))
			set_page_dirty_lock(page);
		put_user_page(page);
	}
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}
EXPORT_SYMBOL(put_user_pages_dirty_lock);

/**
 * put_user_pages() - release an array of gup-pinned pages.
 * @pages:  array of pages to be marked dirty and released.
 * @npages: number of pages in the @pages array.
 *
 * For each page in the @pages array, release the page using put_user_page().
 *
 * Please see the put_user_page() documentation for details.
 */
void put_user_pages(struct page **pages, unsigned long npages)
{
	unsigned long index;

	/*
	 * TODO: this can be optimized for huge pages: if a series of pages is
	 * physically contiguous and part of the same compound page, then a
	 * single operation to the head page should suffice.
	 */
	for (index = 0; index < npages; index++)
		put_user_page(pages[index]);
}
EXPORT_SYMBOL(put_user_pages);

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#ifdef CONFIG_MMU
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static struct page *no_page_table(struct vm_area_struct *vma,
		unsigned int flags)
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{
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	/*
	 * When core dumping an enormous anonymous area that nobody
	 * has touched so far, we don't want to allocate unnecessary pages or
	 * page tables.  Return error instead of NULL to skip handle_mm_fault,
	 * then get_dump_page() will return NULL to leave a hole in the dump.
	 * But we can only make this optimization where a hole would surely
	 * be zero-filled if handle_mm_fault() actually did handle it.
	 */
	if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
		return ERR_PTR(-EFAULT);
	return NULL;
}
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static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
		pte_t *pte, unsigned int flags)
{
	/* No page to get reference */
	if (flags & FOLL_GET)
		return -EFAULT;

	if (flags & FOLL_TOUCH) {
		pte_t entry = *pte;

		if (flags & FOLL_WRITE)
			entry = pte_mkdirty(entry);
		entry = pte_mkyoung(entry);

		if (!pte_same(*pte, entry)) {
			set_pte_at(vma->vm_mm, address, pte, entry);
			update_mmu_cache(vma, address, pte);
		}
	}

	/* Proper page table entry exists, but no corresponding struct page */
	return -EEXIST;
}

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/*
 * FOLL_FORCE can write to even unwritable pte's, but only
 * after we've gone through a COW cycle and they are dirty.
 */
static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
{
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	return pte_write(pte) ||
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		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
}

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static struct page *follow_page_pte(struct vm_area_struct *vma,
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		unsigned long address, pmd_t *pmd, unsigned int flags,
		struct dev_pagemap **pgmap)
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{
	struct mm_struct *mm = vma->vm_mm;
	struct page *page;
	spinlock_t *ptl;
	pte_t *ptep, pte;
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retry:
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	if (unlikely(pmd_bad(*pmd)))
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		return no_page_table(vma, flags);
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	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
	pte = *ptep;
	if (!pte_present(pte)) {
		swp_entry_t entry;
		/*
		 * KSM's break_ksm() relies upon recognizing a ksm page
		 * even while it is being migrated, so for that case we
		 * need migration_entry_wait().
		 */
		if (likely(!(flags & FOLL_MIGRATION)))
			goto no_page;
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		if (pte_none(pte))
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			goto no_page;
		entry = pte_to_swp_entry(pte);
		if (!is_migration_entry(entry))
			goto no_page;
		pte_unmap_unlock(ptep, ptl);
		migration_entry_wait(mm, pmd, address);
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		goto retry;
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	}
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	if ((flags & FOLL_NUMA) && pte_protnone(pte))
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		goto no_page;
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	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
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		pte_unmap_unlock(ptep, ptl);
		return NULL;
	}
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	page = vm_normal_page(vma, address, pte);
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	if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
		/*
		 * Only return device mapping pages in the FOLL_GET case since
		 * they are only valid while holding the pgmap reference.
		 */
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		*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
		if (*pgmap)
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			page = pte_page(pte);
		else
			goto no_page;
	} else if (unlikely(!page)) {
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		if (flags & FOLL_DUMP) {
			/* Avoid special (like zero) pages in core dumps */
			page = ERR_PTR(-EFAULT);
			goto out;
		}

		if (is_zero_pfn(pte_pfn(pte))) {
			page = pte_page(pte);
		} else {
			int ret;

			ret = follow_pfn_pte(vma, address, ptep, flags);
			page = ERR_PTR(ret);
			goto out;
		}
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	}

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	if (flags & FOLL_SPLIT && PageTransCompound(page)) {
		int ret;
		get_page(page);
		pte_unmap_unlock(ptep, ptl);
		lock_page(page);
		ret = split_huge_page(page);
		unlock_page(page);
		put_page(page);
		if (ret)
			return ERR_PTR(ret);
		goto retry;
	}

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	if (flags & FOLL_GET) {
		if (unlikely(!try_get_page(page))) {
			page = ERR_PTR(-ENOMEM);
			goto out;
		}
	}
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	if (flags & FOLL_TOUCH) {
		if ((flags & FOLL_WRITE) &&
		    !pte_dirty(pte) && !PageDirty(page))
			set_page_dirty(page);
		/*
		 * pte_mkyoung() would be more correct here, but atomic care
		 * is needed to avoid losing the dirty bit: it is easier to use
		 * mark_page_accessed().
		 */
		mark_page_accessed(page);
	}
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Eric B Munson committed
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	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
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		/* Do not mlock pte-mapped THP */
		if (PageTransCompound(page))
			goto out;

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		/*
		 * The preliminary mapping check is mainly to avoid the
		 * pointless overhead of lock_page on the ZERO_PAGE
		 * which might bounce very badly if there is contention.
		 *
		 * If the page is already locked, we don't need to
		 * handle it now - vmscan will handle it later if and
		 * when it attempts to reclaim the page.
		 */
		if (page->mapping && trylock_page(page)) {
			lru_add_drain();  /* push cached pages to LRU */
			/*
			 * Because we lock page here, and migration is
			 * blocked by the pte's page reference, and we
			 * know the page is still mapped, we don't even
			 * need to check for file-cache page truncation.
			 */
			mlock_vma_page(page);
			unlock_page(page);
		}
	}
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out:
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	pte_unmap_unlock(ptep, ptl);
	return page;
no_page:
	pte_unmap_unlock(ptep, ptl);
	if (!pte_none(pte))
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		return NULL;
	return no_page_table(vma, flags);
}

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static struct page *follow_pmd_mask(struct vm_area_struct *vma,
				    unsigned long address, pud_t *pudp,
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				    unsigned int flags,
				    struct follow_page_context *ctx)
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{
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	pmd_t *pmd, pmdval;
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	spinlock_t *ptl;
	struct page *page;
	struct mm_struct *mm = vma->vm_mm;

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	pmd = pmd_offset(pudp, address);
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	/*
	 * The READ_ONCE() will stabilize the pmdval in a register or
	 * on the stack so that it will stop changing under the code.
	 */
	pmdval = READ_ONCE(*pmd);
	if (pmd_none(pmdval))
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		return no_page_table(vma, flags);
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	if (pmd_huge(pmdval) && vma->vm_flags & VM_HUGETLB) {
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		page = follow_huge_pmd(mm, address, pmd, flags);
		if (page)
			return page;
		return no_page_table(vma, flags);
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	}
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	if (is_hugepd(__hugepd(pmd_val(pmdval)))) {
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		page = follow_huge_pd(vma, address,
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				      __hugepd(pmd_val(pmdval)), flags,
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				      PMD_SHIFT);
		if (page)
			return page;
		return no_page_table(vma, flags);
	}
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retry:
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	if (!pmd_present(pmdval)) {
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		if (likely(!(flags & FOLL_MIGRATION)))
			return no_page_table(vma, flags);
		VM_BUG_ON(thp_migration_supported() &&
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				  !is_pmd_migration_entry(pmdval));
		if (is_pmd_migration_entry(pmdval))
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			pmd_migration_entry_wait(mm, pmd);
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		pmdval = READ_ONCE(*pmd);
		/*
		 * MADV_DONTNEED may convert the pmd to null because
		 * mmap_sem is held in read mode
		 */
		if (pmd_none(pmdval))
			return no_page_table(vma, flags);
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		goto retry;
	}
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	if (pmd_devmap(pmdval)) {
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		ptl = pmd_lock(mm, pmd);
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		page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
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		spin_unlock(ptl);
		if (page)
			return page;
	}
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	if (likely(!pmd_trans_huge(pmdval)))
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		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
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	if ((flags & FOLL_NUMA) && pmd_protnone(pmdval))
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		return no_page_table(vma, flags);

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retry_locked:
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	ptl = pmd_lock(mm, pmd);
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	if (unlikely(pmd_none(*pmd))) {
		spin_unlock(ptl);
		return no_page_table(vma, flags);
	}
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	if (unlikely(!pmd_present(*pmd))) {
		spin_unlock(ptl);
		if (likely(!(flags & FOLL_MIGRATION)))
			return no_page_table(vma, flags);
		pmd_migration_entry_wait(mm, pmd);
		goto retry_locked;
	}
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	if (unlikely(!pmd_trans_huge(*pmd))) {
		spin_unlock(ptl);
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		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
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	}
	if (flags & FOLL_SPLIT) {
		int ret;
		page = pmd_page(*pmd);
		if (is_huge_zero_page(page)) {
			spin_unlock(ptl);
			ret = 0;
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			split_huge_pmd(vma, pmd, address);
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			if (pmd_trans_unstable(pmd))
				ret = -EBUSY;
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		} else {
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			if (unlikely(!try_get_page(page))) {
				spin_unlock(ptl);
				return ERR_PTR(-ENOMEM);
			}
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			spin_unlock(ptl);
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			lock_page(page);
			ret = split_huge_page(page);
			unlock_page(page);
			put_page(page);
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			if (pmd_none(*pmd))
				return no_page_table(vma, flags);
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		}

		return ret ? ERR_PTR(ret) :
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			follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
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	}
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	page = follow_trans_huge_pmd(vma, address, pmd, flags);
	spin_unlock(ptl);
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	ctx->page_mask = HPAGE_PMD_NR - 1;
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	return page;
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}

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static struct page *follow_pud_mask(struct vm_area_struct *vma,
				    unsigned long address, p4d_t *p4dp,
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				    unsigned int flags,
				    struct follow_page_context *ctx)
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{
	pud_t *pud;
	spinlock_t *ptl;
	struct page *page;
	struct mm_struct *mm = vma->vm_mm;

	pud = pud_offset(p4dp, address);
	if (pud_none(*pud))
		return no_page_table(vma, flags);
	if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
		page = follow_huge_pud(mm, address, pud, flags);
		if (page)
			return page;
		return no_page_table(vma, flags);
	}
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	if (is_hugepd(__hugepd(pud_val(*pud)))) {
		page = follow_huge_pd(vma, address,
				      __hugepd(pud_val(*pud)), flags,
				      PUD_SHIFT);
		if (page)
			return page;
		return no_page_table(vma, flags);
	}
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	if (pud_devmap(*pud)) {
		ptl = pud_lock(mm, pud);
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		page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
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		spin_unlock(ptl);
		if (page)
			return page;
	}
	if (unlikely(pud_bad(*pud)))
		return no_page_table(vma, flags);

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	return follow_pmd_mask(vma, address, pud, flags, ctx);
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}

static struct page *follow_p4d_mask(struct vm_area_struct *vma,
				    unsigned long address, pgd_t *pgdp,
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				    unsigned int flags,
				    struct follow_page_context *ctx)
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{
	p4d_t *p4d;
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	struct page *page;
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	p4d = p4d_offset(pgdp, address);
	if (p4d_none(*p4d))
		return no_page_table(vma, flags);
	BUILD_BUG_ON(p4d_huge(*p4d));
	if (unlikely(p4d_bad(*p4d)))
		return no_page_table(vma, flags);

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	if (is_hugepd(__hugepd(p4d_val(*p4d)))) {
		page = follow_huge_pd(vma, address,
				      __hugepd(p4d_val(*p4d)), flags,
				      P4D_SHIFT);
		if (page)
			return page;
		return no_page_table(vma, flags);
	}
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	return follow_pud_mask(vma, address, p4d, flags, ctx);
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}

/**
 * follow_page_mask - look up a page descriptor from a user-virtual address
 * @vma: vm_area_struct mapping @address
 * @address: virtual address to look up
 * @flags: flags modifying lookup behaviour
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 * @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
 *       pointer to output page_mask
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 *
 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 *
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 * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
 * the device's dev_pagemap metadata to avoid repeating expensive lookups.
 *
 * On output, the @ctx->page_mask is set according to the size of the page.
 *
 * Return: the mapped (struct page *), %NULL if no mapping exists, or
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 * an error pointer if there is a mapping to something not represented
 * by a page descriptor (see also vm_normal_page()).
 */
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static struct page *follow_page_mask(struct vm_area_struct *vma,
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			      unsigned long address, unsigned int flags,
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			      struct follow_page_context *ctx)
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{
	pgd_t *pgd;
	struct page *page;
	struct mm_struct *mm = vma->vm_mm;

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	ctx->page_mask = 0;
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	/* make this handle hugepd */
	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
	if (!IS_ERR(page)) {
		BUG_ON(flags & FOLL_GET);
		return page;
	}

	pgd = pgd_offset(mm, address);

	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
		return no_page_table(vma, flags);

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	if (pgd_huge(*pgd)) {
		page = follow_huge_pgd(mm, address, pgd, flags);
		if (page)
			return page;
		return no_page_table(vma, flags);
	}
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	if (is_hugepd(__hugepd(pgd_val(*pgd)))) {
		page = follow_huge_pd(vma, address,
				      __hugepd(pgd_val(*pgd)), flags,
				      PGDIR_SHIFT);
		if (page)
			return page;
		return no_page_table(vma, flags);
	}
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	return follow_p4d_mask(vma, address, pgd, flags, ctx);
}

struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
			 unsigned int foll_flags)
{
	struct follow_page_context ctx = { NULL };
	struct page *page;

	page = follow_page_mask(vma, address, foll_flags, &ctx);
	if (ctx.pgmap)
		put_dev_pagemap(ctx.pgmap);
	return page;
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}

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static int get_gate_page(struct mm_struct *mm, unsigned long address,
		unsigned int gup_flags, struct vm_area_struct **vma,
		struct page **page)
{
	pgd_t *pgd;
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	p4d_t *p4d;
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	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	int ret = -EFAULT;

	/* user gate pages are read-only */
	if (gup_flags & FOLL_WRITE)
		return -EFAULT;
	if (address > TASK_SIZE)
		pgd = pgd_offset_k(address);
	else
		pgd = pgd_offset_gate(mm, address);
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	if (pgd_none(*pgd))
		return -EFAULT;
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	p4d = p4d_offset(pgd, address);
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	if (p4d_none(*p4d))
		return -EFAULT;
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	pud = pud_offset(p4d, address);
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	if (pud_none(*pud))
		return -EFAULT;
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	pmd = pmd_offset(pud, address);
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	if (!pmd_present(*pmd))
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		return -EFAULT;
	VM_BUG_ON(pmd_trans_huge(*pmd));
	pte = pte_offset_map(pmd, address);
	if (pte_none(*pte))
		goto unmap;
	*vma = get_gate_vma(mm);
	if (!page)
		goto out;
	*page = vm_normal_page(*vma, address, *pte);
	if (!*page) {
		if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
			goto unmap;
		*page = pte_page(*pte);
	}
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	if (unlikely(!try_get_page(*page))) {
		ret = -ENOMEM;
		goto unmap;
	}
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out:
	ret = 0;
unmap:
	pte_unmap(pte);
	return ret;
}

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/*
 * mmap_sem must be held on entry.  If @nonblocking != NULL and
 * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
 * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
 */
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static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
		unsigned long address, unsigned int *flags, int *nonblocking)
{
	unsigned int fault_flags = 0;
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	vm_fault_t ret;
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Eric B Munson's avatar
Eric B Munson committed
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	/* mlock all present pages, but do not fault in new pages */
	if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
		return -ENOENT;
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	if (*flags & FOLL_WRITE)
		fault_flags |= FAULT_FLAG_WRITE;
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	if (*flags & FOLL_REMOTE)
		fault_flags |= FAULT_FLAG_REMOTE;
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	if (nonblocking)
		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
	if (*flags & FOLL_NOWAIT)
		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
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	if (*flags & FOLL_TRIED) {
		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
		fault_flags |= FAULT_FLAG_TRIED;
	}
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636
	ret = handle_mm_fault(vma, address, fault_flags);
637
	if (ret & VM_FAULT_ERROR) {
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		int err = vm_fault_to_errno(ret, *flags);

		if (err)
			return err;
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		BUG();
	}

	if (tsk) {
		if (ret & VM_FAULT_MAJOR)
			tsk->maj_flt++;
		else
			tsk->min_flt++;
	}

	if (ret & VM_FAULT_RETRY) {
653
		if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
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			*nonblocking = 0;
		return -EBUSY;
	}

	/*
	 * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
	 * necessary, even if maybe_mkwrite decided not to set pte_write. We
	 * can thus safely do subsequent page lookups as if they were reads.
	 * But only do so when looping for pte_write is futile: in some cases
	 * userspace may also be wanting to write to the gotten user page,
	 * which a read fault here might prevent (a readonly page might get
	 * reCOWed by userspace write).
	 */
	if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
668
		*flags |= FOLL_COW;
669 670 671
	return 0;
}

672 673 674
static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
{
	vm_flags_t vm_flags = vma->vm_flags;
675 676
	int write = (gup_flags & FOLL_WRITE);
	int foreign = (gup_flags & FOLL_REMOTE);
677 678 679 680

	if (vm_flags & (VM_IO | VM_PFNMAP))
		return -EFAULT;

681 682 683
	if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
		return -EFAULT;

684
	if (write) {
685 686 687 688 689 690 691 692 693 694 695 696
		if (!(vm_flags & VM_WRITE)) {
			if (!(gup_flags & FOLL_FORCE))
				return -EFAULT;
			/*
			 * We used to let the write,force case do COW in a
			 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
			 * set a breakpoint in a read-only mapping of an
			 * executable, without corrupting the file (yet only
			 * when that file had been opened for writing!).
			 * Anon pages in shared mappings are surprising: now
			 * just reject it.
			 */
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			if (!is_cow_mapping(vm_flags))
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				return -EFAULT;
		}
	} else if (!(vm_flags & VM_READ)) {
		if (!(gup_flags & FOLL_FORCE))
			return -EFAULT;
		/*
		 * Is there actually any vma we can reach here which does not
		 * have VM_MAYREAD set?
		 */
		if (!(vm_flags & VM_MAYREAD))
			return -EFAULT;
	}
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	/*
	 * gups are always data accesses, not instruction
	 * fetches, so execute=false here
	 */
	if (!arch_vma_access_permitted(vma, write, false, foreign))
715
		return -EFAULT;
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	return 0;
}

719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738
/**
 * __get_user_pages() - pin user pages in memory
 * @tsk:	task_struct of target task
 * @mm:		mm_struct of target mm
 * @start:	starting user address
 * @nr_pages:	number of pages from start to pin
 * @gup_flags:	flags modifying pin behaviour
 * @pages:	array that receives pointers to the pages pinned.
 *		Should be at least nr_pages long. Or NULL, if caller
 *		only intends to ensure the pages are faulted in.
 * @vmas:	array of pointers to vmas corresponding to each page.
 *		Or NULL if the caller does not require them.
 * @nonblocking: whether waiting for disk IO or mmap_sem contention
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
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 * Must be called with mmap_sem held.  It may be released.  See below.
740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761
 *
 * __get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * __get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
 * appropriate) must be called after the page is finished with, and
 * before put_page is called.
 *
 * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
 * or mmap_sem contention, and if waiting is needed to pin all pages,
762 763 764 765 766 767 768 769
 * *@nonblocking will be set to 0.  Further, if @gup_flags does not
 * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
 * this case.
 *
 * A caller using such a combination of @nonblocking and @gup_flags
 * must therefore hold the mmap_sem for reading only, and recognize
 * when it's been released.  Otherwise, it must be held for either
 * reading or writing and will not be released.
770 771 772 773 774
 *
 * In most cases, get_user_pages or get_user_pages_fast should be used
 * instead of __get_user_pages. __get_user_pages should be used only if
 * you need some special @gup_flags.
 */
775
static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
776 777 778 779
		unsigned long start, unsigned long nr_pages,
		unsigned int gup_flags, struct page **pages,
		struct vm_area_struct **vmas, int *nonblocking)
{
780
	long ret = 0, i = 0;
781
	struct vm_area_struct *vma = NULL;
782
	struct follow_page_context ctx = { NULL };
783 784 785 786 787 788 789 790 791 792 793 794 795 796 797

	if (!nr_pages)
		return 0;

	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

	/*
	 * If FOLL_FORCE is set then do not force a full fault as the hinting
	 * fault information is unrelated to the reference behaviour of a task
	 * using the address space
	 */
	if (!(gup_flags & FOLL_FORCE))
		gup_flags |= FOLL_NUMA;

	do {
798 799 800 801 802 803 804 805 806 807 808 809
		struct page *page;
		unsigned int foll_flags = gup_flags;
		unsigned int page_increm;

		/* first iteration or cross vma bound */
		if (!vma || start >= vma->vm_end) {
			vma = find_extend_vma(mm, start);
			if (!vma && in_gate_area(mm, start)) {
				ret = get_gate_page(mm, start & PAGE_MASK,
						gup_flags, &vma,
						pages ? &pages[i] : NULL);
				if (ret)
810
					goto out;
811
				ctx.page_mask = 0;
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				goto next_page;
			}
814

815 816 817 818
			if (!vma || check_vma_flags(vma, gup_flags)) {
				ret = -EFAULT;
				goto out;
			}
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			if (is_vm_hugetlb_page(vma)) {
				i = follow_hugetlb_page(mm, vma, pages, vmas,
						&start, &nr_pages, i,
822
						gup_flags, nonblocking);
823
				continue;
824
			}
825 826 827 828 829 830
		}
retry:
		/*
		 * If we have a pending SIGKILL, don't keep faulting pages and
		 * potentially allocating memory.
		 */
831
		if (fatal_signal_pending(current)) {
832 833 834
			ret = -ERESTARTSYS;
			goto out;
		}
835
		cond_resched();
836 837

		page = follow_page_mask(vma, start, foll_flags, &ctx);
838 839 840 841 842 843
		if (!page) {
			ret = faultin_page(tsk, vma, start, &foll_flags,
					nonblocking);
			switch (ret) {
			case 0:
				goto retry;
844 845 846
			case -EBUSY:
				ret = 0;
				/* FALLTHRU */
847 848 849
			case -EFAULT:
			case -ENOMEM:
			case -EHWPOISON:
850
				goto out;
851 852
			case -ENOENT:
				goto next_page;
853
			}
854
			BUG();
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		} else if (PTR_ERR(page) == -EEXIST) {
			/*
			 * Proper page table entry exists, but no corresponding
			 * struct page.
			 */
			goto next_page;
		} else if (IS_ERR(page)) {
862 863
			ret = PTR_ERR(page);
			goto out;
864
		}
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		if (pages) {
			pages[i] = page;
			flush_anon_page(vma, page, start);
			flush_dcache_page(page);
869
			ctx.page_mask = 0;
870 871
		}
next_page:
872 873
		if (vmas) {
			vmas[i] = vma;
874
			ctx.page_mask = 0;
875
		}
876
		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
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		if (page_increm > nr_pages)
			page_increm = nr_pages;
		i += page_increm;
		start += page_increm * PAGE_SIZE;
		nr_pages -= page_increm;
882
	} while (nr_pages);
883 884 885 886
out:
	if (ctx.pgmap)
		put_dev_pagemap(ctx.pgmap);
	return i ? i : ret;
887 888
}

889 890
static bool vma_permits_fault(struct vm_area_struct *vma,
			      unsigned int fault_flags)
891
{
892 893
	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
894
	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
895 896 897 898

	if (!(vm_flags & vma->vm_flags))
		return false;

899 900
	/*
	 * The architecture might have a hardware protection
901
	 * mechanism other than read/write that can deny access.
902 903 904
	 *
	 * gup always represents data access, not instruction
	 * fetches, so execute=false here:
905
	 */
906
	if (!arch_vma_access_permitted(vma, write, false, foreign))
907 908
		return false;

909 910 911
	return true;
}

912 913 914 915 916 917 918
/*
 * fixup_user_fault() - manually resolve a user page fault
 * @tsk:	the task_struct to use for page fault accounting, or
 *		NULL if faults are not to be recorded.
 * @mm:		mm_struct of target mm
 * @address:	user address
 * @fault_flags:flags to pass down to handle_mm_fault()
919 920
 * @unlocked:	did we unlock the mmap_sem while retrying, maybe NULL if caller
 *		does not allow retry
921 922 923 924 925 926 927 928 929 930 931
 *
 * This is meant to be called in the specific scenario where for locking reasons
 * we try to access user memory in atomic context (within a pagefault_disable()
 * section), this returns -EFAULT, and we want to resolve the user fault before
 * trying again.
 *
 * Typically this is meant to be used by the futex code.
 *
 * The main difference with get_user_pages() is that this function will
 * unconditionally call handle_mm_fault() which will in turn perform all the
 * necessary SW fixup of the dirty and young bits in the PTE, while
932
 * get_user_pages() only guarantees to update these in the struct page.
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 *
 * This is important for some architectures where those bits also gate the
 * access permission to the page because they are maintained in software.  On
 * such architectures, gup() will not be enough to make a subsequent access
 * succeed.
 *
939 940
 * This function will not return with an unlocked mmap_sem. So it has not the
 * same semantics wrt the @mm->mmap_sem as does filemap_fault().
941 942
 */
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
943 944
		     unsigned long address, unsigned int fault_flags,
		     bool *unlocked)
945 946
{
	struct vm_area_struct *vma;
947
	vm_fault_t ret, major = 0;
948 949 950

	if (unlocked)
		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
951

952
retry:
953 954 955 956
	vma = find_extend_vma(mm, address);
	if (!vma || address < vma->vm_start)
		return -EFAULT;

957
	if (!vma_permits_fault(vma, fault_flags))
958 959
		return -EFAULT;

960
	ret = handle_mm_fault(vma, address, fault_flags);
961
	major |= ret & VM_FAULT_MAJOR;
962
	if (ret & VM_FAULT_ERROR) {
963 964 965 966
		int err = vm_fault_to_errno(ret, 0);

		if (err)
			return err;
967 968
		BUG();
	}
969 970 971 972 973 974 975 976 977 978 979

	if (ret & VM_FAULT_RETRY) {
		down_read(&mm->mmap_sem);
		if (!(fault_flags & FAULT_FLAG_TRIED)) {
			*unlocked = true;
			fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
			fault_flags |= FAULT_FLAG_TRIED;
			goto retry;
		}
	}

980
	if (tsk) {
981
		if (major)
982 983 984 985 986 987
			tsk->maj_flt++;
		else
			tsk->min_flt++;
	}
	return 0;
}
988
EXPORT_SYMBOL_GPL(fixup_user_fault);
989

990 991 992 993 994 995
static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
						struct mm_struct *mm,
						unsigned long start,
						unsigned long nr_pages,
						struct page **pages,
						struct vm_area_struct **vmas,
996
						int *locked,
997
						unsigned int flags)
998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033
{
	long ret, pages_done;
	bool lock_dropped;

	if (locked) {
		/* if VM_FAULT_RETRY can be returned, vmas become invalid */
		BUG_ON(vmas);
		/* check caller initialized locked */
		BUG_ON(*locked != 1);
	}

	if (pages)
		flags |= FOLL_GET;

	pages_done = 0;
	lock_dropped = false;
	for (;;) {
		ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
				       vmas, locked);
		if (!locked)
			/* VM_FAULT_RETRY couldn't trigger, bypass */
			return ret;

		/* VM_FAULT_RETRY cannot return errors */
		if (!*locked) {
			BUG_ON(ret < 0);
			BUG_ON(ret >= nr_pages);
		}

		if (ret > 0) {
			nr_pages -= ret;
			pages_done += ret;
			if (!nr_pages)
				break;
		}
		if (*locked) {
1034 1035 1036 1037
			/*
			 * VM_FAULT_RETRY didn't trigger or it was a
			 * FOLL_NOWAIT.
			 */
1038 1039 1040 1041
			if (!pages_done)
				pages_done = ret;
			break;
		}
1042 1043 1044 1045 1046 1047
		/*
		 * VM_FAULT_RETRY triggered, so seek to the faulting offset.
		 * For the prefault case (!pages) we only update counts.
		 */
		if (likely(pages))
			pages += ret;
1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069
		start += ret << PAGE_SHIFT;

		/*
		 * Repeat on the address that fired VM_FAULT_RETRY
		 * without FAULT_FLAG_ALLOW_RETRY but with
		 * FAULT_FLAG_TRIED.
		 */
		*locked = 1;
		lock_dropped = true;
		down_read(&mm->mmap_sem);
		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
				       pages, NULL, NULL);
		if (ret != 1) {
			BUG_ON(ret > 1);
			if (!pages_done)
				pages_done = ret;
			break;
		}
		nr_pages--;
		pages_done++;
		if (!nr_pages)
			break;
1070 1071
		if (likely(pages))
			pages++;
1072 1073
		start += PAGE_SIZE;
	}
1074
	if (lock_dropped && *locked) {
1075 1076 1077 1078 1079 1080 1081 1082 1083 1084
		/*
		 * We must let the caller know we temporarily dropped the lock
		 * and so the critical section protected by it was lost.
		 */
		up_read(&mm->mmap_sem);
		*locked = 0;
	}
	return pages_done;
}

1085
/*
1086
 * get_user_pages_remote() - pin user pages in memory
1087 1088 1089 1090 1091
 * @tsk:	the task_struct to use for page fault accounting, or
 *		NULL if faults are not to be recorded.
 * @mm:		mm_struct of target mm
 * @start:	starting user address
 * @nr_pages:	number of pages from start to pin
1092
 * @gup_flags:	flags modifying lookup behaviour
1093 1094 1095 1096 1097
 * @pages:	array that receives pointers to the pages pinned.
 *		Should be at least nr_pages long. Or NULL, if caller
 *		only intends to ensure the pages are faulted in.
 * @vmas:	array of pointers to vmas corresponding to each page.
 *		Or NULL if the caller does not require them.
1098 1099 1100
 * @locked:	pointer to lock flag indicating whether lock is held and
 *		subsequently whether VM_FAULT_RETRY functionality can be
 *		utilised. Lock must initially be held.
1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
 * Must be called with mmap_sem held for read or write.
 *
 * get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
1124 1125 1126
 * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
 * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
 * be called after the page is finished with, and before put_page is called.
1127 1128 1129 1130 1131 1132 1133 1134
 *
 * get_user_pages is typically used for fewer-copy IO operations, to get a
 * handle on the memory by some means other than accesses via the user virtual
 * addresses. The pages may be submitted for DMA to devices or accessed via
 * their kernel linear mapping (via the kmap APIs). Care should be taken to
 * use the correct cache flushing APIs.
 *
 * See also get_user_pages_fast, for performance critical applications.
1135 1136 1137 1138 1139
 *
 * get_user_pages should be phased out in favor of
 * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
 * should use get_user_pages because it cannot pass
 * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
1140
 */
1141 1142
long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
		unsigned long start, unsigned long nr_pages,
1143
		unsigned int gup_flags, struct page **pages,
1144
		struct vm_area_struct **vmas, int *locked)
1145
{
1146 1147 1148 1149 1150 1151 1152 1153 1154
	/*
	 * FIXME: Current FOLL_LONGTERM behavior is incompatible with
	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
	 * vmas.  As there are no users of this flag in this call we simply
	 * disallow this option for now.
	 */
	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
		return -EINVAL;

1155
	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
1156
				       locked,