gup.c 51.0 KB
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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 <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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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)
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		get_page(page);
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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);
	}
E
Eric B Munson 已提交
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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 {
			get_page(page);
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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
 * @page_mask: on output, *page_mask is set according to the size of the page
 *
 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 *
 * Returns the mapped (struct page *), %NULL if no mapping exists, or
 * an error pointer if there is a mapping to something not represented
 * by a page descriptor (see also vm_normal_page()).
 */
struct page *follow_page_mask(struct vm_area_struct *vma,
			      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);
	BUG_ON(pgd_none(*pgd));
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	p4d = p4d_offset(pgd, address);
	BUG_ON(p4d_none(*p4d));
	pud = pud_offset(p4d, address);
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	BUG_ON(pud_none(*pud));
	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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		/*
		 * This should never happen (a device public page in the gate
		 * area).
		 */
		if (is_device_public_page(*page))
			goto unmap;
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	}
	get_page(*page);
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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E
Eric B Munson 已提交
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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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529
	ret = handle_mm_fault(vma, address, fault_flags);
530
	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) {
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		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))
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		*flags |= FOLL_COW;
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	return 0;
}

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static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
{
	vm_flags_t vm_flags = vma->vm_flags;
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	int write = (gup_flags & FOLL_WRITE);
	int foreign = (gup_flags & FOLL_REMOTE);
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	if (vm_flags & (VM_IO | VM_PFNMAP))
		return -EFAULT;

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

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	if (write) {
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		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))
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		return -EFAULT;
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	return 0;
}

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/**
 * __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.
 *
632
 * Must be called with mmap_sem held.  It may be released.  See below.
633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654
 *
 * __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,
655 656 657 658 659 660 661 662
 * *@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.
663 664 665 666 667
 *
 * 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.
 */
L
Lorenzo Stoakes 已提交
668
static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
669 670 671 672
		unsigned long start, unsigned long nr_pages,
		unsigned int gup_flags, struct page **pages,
		struct vm_area_struct **vmas, int *nonblocking)
{
673
	long ret = 0, i = 0;
674
	struct vm_area_struct *vma = NULL;
675
	struct follow_page_context ctx = { NULL };
676 677 678 679 680 681 682 683 684 685 686 687 688 689 690

	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 {
691 692 693 694 695 696 697 698 699 700 701 702 703 704
		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)) {
				int ret;
				ret = get_gate_page(mm, start & PAGE_MASK,
						gup_flags, &vma,
						pages ? &pages[i] : NULL);
				if (ret)
					return i ? : ret;
705
				ctx.page_mask = 0;
706 707
				goto next_page;
			}
708

709 710 711 712
			if (!vma || check_vma_flags(vma, gup_flags)) {
				ret = -EFAULT;
				goto out;
			}
713 714 715
			if (is_vm_hugetlb_page(vma)) {
				i = follow_hugetlb_page(mm, vma, pages, vmas,
						&start, &nr_pages, i,
716
						gup_flags, nonblocking);
717
				continue;
718
			}
719 720 721 722 723 724
		}
retry:
		/*
		 * If we have a pending SIGKILL, don't keep faulting pages and
		 * potentially allocating memory.
		 */
725 726 727 728
		if (unlikely(fatal_signal_pending(current))) {
			ret = -ERESTARTSYS;
			goto out;
		}
729
		cond_resched();
730 731

		page = follow_page_mask(vma, start, foll_flags, &ctx);
732 733 734 735 736 737
		if (!page) {
			ret = faultin_page(tsk, vma, start, &foll_flags,
					nonblocking);
			switch (ret) {
			case 0:
				goto retry;
738 739 740
			case -EBUSY:
				ret = 0;
				/* FALLTHRU */
741 742 743
			case -EFAULT:
			case -ENOMEM:
			case -EHWPOISON:
744
				goto out;
745 746
			case -ENOENT:
				goto next_page;
747
			}
748
			BUG();
749 750 751 752 753 754 755
		} else if (PTR_ERR(page) == -EEXIST) {
			/*
			 * Proper page table entry exists, but no corresponding
			 * struct page.
			 */
			goto next_page;
		} else if (IS_ERR(page)) {
756 757
			ret = PTR_ERR(page);
			goto out;
758
		}
759 760 761 762
		if (pages) {
			pages[i] = page;
			flush_anon_page(vma, page, start);
			flush_dcache_page(page);
763
			ctx.page_mask = 0;
764 765
		}
next_page:
766 767
		if (vmas) {
			vmas[i] = vma;
768
			ctx.page_mask = 0;
769
		}
770
		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
771 772 773 774 775
		if (page_increm > nr_pages)
			page_increm = nr_pages;
		i += page_increm;
		start += page_increm * PAGE_SIZE;
		nr_pages -= page_increm;
776
	} while (nr_pages);
777 778 779 780
out:
	if (ctx.pgmap)
		put_dev_pagemap(ctx.pgmap);
	return i ? i : ret;
781 782
}

783 784
static bool vma_permits_fault(struct vm_area_struct *vma,
			      unsigned int fault_flags)
785
{
786 787
	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
788
	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
789 790 791 792

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

793 794
	/*
	 * The architecture might have a hardware protection
795
	 * mechanism other than read/write that can deny access.
796 797 798
	 *
	 * gup always represents data access, not instruction
	 * fetches, so execute=false here:
799
	 */
800
	if (!arch_vma_access_permitted(vma, write, false, foreign))
801 802
		return false;

803 804 805
	return true;
}

806 807 808 809 810 811 812
/*
 * 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()
813 814
 * @unlocked:	did we unlock the mmap_sem while retrying, maybe NULL if caller
 *		does not allow retry
815 816 817 818 819 820 821 822 823 824 825
 *
 * 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
826
 * get_user_pages() only guarantees to update these in the struct page.
827 828 829 830 831 832
 *
 * 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.
 *
833 834
 * 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().
835 836
 */
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
837 838
		     unsigned long address, unsigned int fault_flags,
		     bool *unlocked)
839 840
{
	struct vm_area_struct *vma;
841
	vm_fault_t ret, major = 0;
842 843 844

	if (unlocked)
		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
845

846
retry:
847 848 849 850
	vma = find_extend_vma(mm, address);
	if (!vma || address < vma->vm_start)
		return -EFAULT;

851
	if (!vma_permits_fault(vma, fault_flags))
852 853
		return -EFAULT;

854
	ret = handle_mm_fault(vma, address, fault_flags);
855
	major |= ret & VM_FAULT_MAJOR;
856
	if (ret & VM_FAULT_ERROR) {
857 858 859 860
		int err = vm_fault_to_errno(ret, 0);

		if (err)
			return err;
861 862
		BUG();
	}
863 864 865 866 867 868 869 870 871 872 873

	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;
		}
	}

874
	if (tsk) {
875
		if (major)
876 877 878 879 880 881
			tsk->maj_flt++;
		else
			tsk->min_flt++;
	}
	return 0;
}
882
EXPORT_SYMBOL_GPL(fixup_user_fault);
883

884 885 886 887 888 889
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,
890
						int *locked,
891
						unsigned int flags)
892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931
{
	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 (!pages)
			/* If it's a prefault don't insist harder */
			return ret;

		if (ret > 0) {
			nr_pages -= ret;
			pages_done += ret;
			if (!nr_pages)
				break;
		}
		if (*locked) {
932 933 934 935
			/*
			 * VM_FAULT_RETRY didn't trigger or it was a
			 * FOLL_NOWAIT.
			 */
936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966
			if (!pages_done)
				pages_done = ret;
			break;
		}
		/* VM_FAULT_RETRY triggered, so seek to the faulting offset */
		pages += ret;
		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;
		pages++;
		start += PAGE_SIZE;
	}
967
	if (lock_dropped && *locked) {
968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998
		/*
		 * 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;
}

/*
 * We can leverage the VM_FAULT_RETRY functionality in the page fault
 * paths better by using either get_user_pages_locked() or
 * get_user_pages_unlocked().
 *
 * get_user_pages_locked() is suitable to replace the form:
 *
 *      down_read(&mm->mmap_sem);
 *      do_something()
 *      get_user_pages(tsk, mm, ..., pages, NULL);
 *      up_read(&mm->mmap_sem);
 *
 *  to:
 *
 *      int locked = 1;
 *      down_read(&mm->mmap_sem);
 *      do_something()
 *      get_user_pages_locked(tsk, mm, ..., pages, &locked);
 *      if (locked)
 *          up_read(&mm->mmap_sem);
 */
999
long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
1000
			   unsigned int gup_flags, struct page **pages,
1001 1002
			   int *locked)
{
1003
	return __get_user_pages_locked(current, current->mm, start, nr_pages,
1004
				       pages, NULL, locked,
1005
				       gup_flags | FOLL_TOUCH);
1006
}
1007
EXPORT_SYMBOL(get_user_pages_locked);
1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020

/*
 * get_user_pages_unlocked() is suitable to replace the form:
 *
 *      down_read(&mm->mmap_sem);
 *      get_user_pages(tsk, mm, ..., pages, NULL);
 *      up_read(&mm->mmap_sem);
 *
 *  with:
 *
 *      get_user_pages_unlocked(tsk, mm, ..., pages);
 *
 * It is functionally equivalent to get_user_pages_fast so
1021 1022
 * get_user_pages_fast should be used instead if specific gup_flags
 * (e.g. FOLL_FORCE) are not required.
1023
 */
1024
long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
1025
			     struct page **pages, unsigned int gup_flags)
1026
{
1027 1028 1029 1030 1031 1032
	struct mm_struct *mm = current->mm;
	int locked = 1;
	long ret;

	down_read(&mm->mmap_sem);
	ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
1033
				      &locked, gup_flags | FOLL_TOUCH);
1034 1035 1036
	if (locked)
		up_read(&mm->mmap_sem);
	return ret;
1037
}
1038
EXPORT_SYMBOL(get_user_pages_unlocked);
1039

1040
/*
1041
 * get_user_pages_remote() - pin user pages in memory
1042 1043 1044 1045 1046
 * @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
1047
 * @gup_flags:	flags modifying lookup behaviour
1048 1049 1050 1051 1052
 * @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.
1053 1054 1055
 * @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.
1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078
 *
 * 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.
 *
1079 1080 1081
 * 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.
1082 1083 1084 1085 1086 1087 1088 1089
 *
 * 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.
1090 1091 1092 1093 1094
 *
 * 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.
1095
 */
1096 1097
long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
		unsigned long start, unsigned long nr_pages,
1098
		unsigned int gup_flags, struct page **pages,
1099
		struct vm_area_struct **vmas, int *locked)
1100
{
1101
	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
1102
				       locked,
1103
				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
1104 1105 1106 1107
}
EXPORT_SYMBOL(get_user_pages_remote);

/*
1108 1109
 * This is the same as get_user_pages_remote(), just with a
 * less-flexible calling convention where we assume that the task
1110 1111 1112
 * and mm being operated on are the current task's and don't allow
 * passing of a locked parameter.  We also obviously don't pass
 * FOLL_REMOTE in here.
1113
 */
1114
long get_user_pages(unsigned long start, unsigned long nr_pages,
1115
		unsigned int gup_flags, struct page **pages,
1116 1117
		struct vm_area_struct **vmas)
{
1118
	return __get_user_pages_locked(current, current->mm, start, nr_pages,
1119
				       pages, vmas, NULL,
1120
				       gup_flags | FOLL_TOUCH);
1121
}
1122
EXPORT_SYMBOL(get_user_pages);
1123

1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187
#ifdef CONFIG_FS_DAX
/*
 * This is the same as get_user_pages() in that it assumes we are
 * operating on the current task's mm, but it goes further to validate
 * that the vmas associated with the address range are suitable for
 * longterm elevated page reference counts. For example, filesystem-dax
 * mappings are subject to the lifetime enforced by the filesystem and
 * we need guarantees that longterm users like RDMA and V4L2 only
 * establish mappings that have a kernel enforced revocation mechanism.
 *
 * "longterm" == userspace controlled elevated page count lifetime.
 * Contrast this to iov_iter_get_pages() usages which are transient.
 */
long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
		unsigned int gup_flags, struct page **pages,
		struct vm_area_struct **vmas_arg)
{
	struct vm_area_struct **vmas = vmas_arg;
	struct vm_area_struct *vma_prev = NULL;
	long rc, i;

	if (!pages)
		return -EINVAL;

	if (!vmas) {
		vmas = kcalloc(nr_pages, sizeof(struct vm_area_struct *),
			       GFP_KERNEL);
		if (!vmas)
			return -ENOMEM;
	}

	rc = get_user_pages(start, nr_pages, gup_flags, pages, vmas);

	for (i = 0; i < rc; i++) {
		struct vm_area_struct *vma = vmas[i];

		if (vma == vma_prev)
			continue;

		vma_prev = vma;

		if (vma_is_fsdax(vma))
			break;
	}

	/*
	 * Either get_user_pages() failed, or the vma validation
	 * succeeded, in either case we don't need to put_page() before
	 * returning.
	 */
	if (i >= rc)
		goto out;

	for (i = 0; i < rc; i++)
		put_page(pages[i]);
	rc = -EOPNOTSUPP;
out:
	if (vmas != vmas_arg)
		kfree(vmas);
	return rc;
}
EXPORT_SYMBOL(get_user_pages_longterm);
#endif /* CONFIG_FS_DAX */

1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219
/**
 * populate_vma_page_range() -  populate a range of pages in the vma.
 * @vma:   target vma
 * @start: start address
 * @end:   end address
 * @nonblocking:
 *
 * This takes care of mlocking the pages too if VM_LOCKED is set.
 *
 * return 0 on success, negative error code on error.
 *
 * vma->vm_mm->mmap_sem must be held.
 *
 * If @nonblocking is NULL, it may be held for read or write and will
 * be unperturbed.
 *
 * If @nonblocking is non-NULL, it must held for read only and may be
 * released.  If it's released, *@nonblocking will be set to 0.
 */
long populate_vma_page_range(struct vm_area_struct *vma,
		unsigned long start, unsigned long end, int *nonblocking)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long nr_pages = (end - start) / PAGE_SIZE;
	int gup_flags;

	VM_BUG_ON(start & ~PAGE_MASK);
	VM_BUG_ON(end   & ~PAGE_MASK);
	VM_BUG_ON_VMA(start < vma->vm_start, vma);
	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);

E
Eric B Munson 已提交
1220 1221 1222
	gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
	if (vma->vm_flags & VM_LOCKONFAULT)
		gup_flags &= ~FOLL_POPULATE;
1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305
	/*
	 * We want to touch writable mappings with a write fault in order
	 * to break COW, except for shared mappings because these don't COW
	 * and we would not want to dirty them for nothing.
	 */
	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
		gup_flags |= FOLL_WRITE;

	/*
	 * We want mlock to succeed for regions that have any permissions
	 * other than PROT_NONE.
	 */
	if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
		gup_flags |= FOLL_FORCE;

	/*
	 * We made sure addr is within a VMA, so the following will
	 * not result in a stack expansion that recurses back here.
	 */
	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
				NULL, NULL, nonblocking);
}

/*
 * __mm_populate - populate and/or mlock pages within a range of address space.
 *
 * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
 * flags. VMAs must be already marked with the desired vm_flags, and
 * mmap_sem must not be held.
 */
int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
{
	struct mm_struct *mm = current->mm;
	unsigned long end, nstart, nend;
	struct vm_area_struct *vma = NULL;
	int locked = 0;
	long ret = 0;

	end = start + len;

	for (nstart = start; nstart < end; nstart = nend) {
		/*
		 * We want to fault in pages for [nstart; end) address range.
		 * Find first corresponding VMA.
		 */
		if (!locked) {
			locked = 1;
			down_read(&mm->mmap_sem);
			vma = find_vma(mm, nstart);
		} else if (nstart >= vma->vm_end)
			vma = vma->vm_next;
		if (!vma || vma->vm_start >= end)
			break;
		/*
		 * Set [nstart; nend) to intersection of desired address
		 * range with the first VMA. Also, skip undesirable VMA types.
		 */
		nend = min(end, vma->vm_end);
		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
			continue;
		if (nstart < vma->vm_start)
			nstart = vma->vm_start;
		/*
		 * Now fault in a range of pages. populate_vma_page_range()
		 * double checks the vma flags, so that it won't mlock pages
		 * if the vma was already munlocked.
		 */
		ret = populate_vma_page_range(vma, nstart, nend, &locked);
		if (ret < 0) {
			if (ignore_errors) {
				ret = 0;
				continue;	/* continue at next VMA */
			}
			break;
		}
		nend = nstart + ret * PAGE_SIZE;
		ret = 0;
	}
	if (locked)
		up_read(&mm->mmap_sem);
	return ret;	/* 0 or negative error code */
}

1306 1307 1308 1309 1310
/**
 * get_dump_page() - pin user page in memory while writing it to core dump
 * @addr: user address
 *
 * Returns struct page pointer of user page pinned for dump,
1311
 * to be freed afterwards by put_page().
1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333
 *
 * Returns NULL on any kind of failure - a hole must then be inserted into
 * the corefile, to preserve alignment with its headers; and also returns
 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
 * allowing a hole to be left in the corefile to save diskspace.
 *
 * Called without mmap_sem, but after all other threads have been killed.
 */
#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
	struct vm_area_struct *vma;
	struct page *page;

	if (__get_user_pages(current, current->mm, addr, 1,
			     FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
			     NULL) < 1)
		return NULL;
	flush_cache_page(vma, addr, page_to_pfn(page));
	return page;
}
#endif /* CONFIG_ELF_CORE */
1334 1335

/*
1336
 * Generic Fast GUP
1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356
 *
 * get_user_pages_fast attempts to pin user pages by walking the page
 * tables directly and avoids taking locks. Thus the walker needs to be
 * protected from page table pages being freed from under it, and should
 * block any THP splits.
 *
 * One way to achieve this is to have the walker disable interrupts, and
 * rely on IPIs from the TLB flushing code blocking before the page table
 * pages are freed. This is unsuitable for architectures that do not need
 * to broadcast an IPI when invalidating TLBs.
 *
 * Another way to achieve this is to batch up page table containing pages
 * belonging to more than one mm_user, then rcu_sched a callback to free those
 * pages. Disabling interrupts will allow the fast_gup walker to both block
 * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
 * (which is a relatively rare event). The code below adopts this strategy.
 *
 * Before activating this code, please be aware that the following assumptions
 * are currently made:
 *
1357 1358
 *  *) Either HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
 *  free pages containing page tables or TLB flushing requires IPI broadcast.
1359 1360 1361 1362 1363 1364 1365 1366 1367
 *
 *  *) ptes can be read atomically by the architecture.
 *
 *  *) access_ok is sufficient to validate userspace address ranges.
 *
 * The last two assumptions can be relaxed by the addition of helper functions.
 *
 * This code is based heavily on the PowerPC implementation by Nick Piggin.
 */
1368
#ifdef CONFIG_HAVE_GENERIC_GUP
1369

1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380
#ifndef gup_get_pte
/*
 * We assume that the PTE can be read atomically. If this is not the case for
 * your architecture, please provide the helper.
 */
static inline pte_t gup_get_pte(pte_t *ptep)
{
	return READ_ONCE(*ptep);
}
#endif

1381 1382 1383 1384 1385 1386 1387 1388 1389 1390
static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
{
	while ((*nr) - nr_start) {
		struct page *page = pages[--(*nr)];

		ClearPageReferenced(page);
		put_page(page);
	}
}

1391
#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
1392 1393 1394
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
			 int write, struct page **pages, int *nr)
{
1395 1396
	struct dev_pagemap *pgmap = NULL;
	int nr_start = *nr, ret = 0;
1397 1398 1399 1400
	pte_t *ptep, *ptem;

	ptem = ptep = pte_offset_map(&pmd, addr);
	do {
1401
		pte_t pte = gup_get_pte(ptep);
1402
		struct page *head, *page;
1403 1404 1405

		/*
		 * Similar to the PMD case below, NUMA hinting must take slow
1406
		 * path using the pte_protnone check.
1407
		 */
1408 1409 1410 1411 1412 1413
		if (pte_protnone(pte))
			goto pte_unmap;

		if (!pte_access_permitted(pte, write))
			goto pte_unmap;

1414 1415 1416 1417 1418 1419 1420
		if (pte_devmap(pte)) {
			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
			if (unlikely(!pgmap)) {
				undo_dev_pagemap(nr, nr_start, pages);
				goto pte_unmap;
			}
		} else if (pte_special(pte))
1421 1422 1423 1424
			goto pte_unmap;

		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
		page = pte_page(pte);
1425
		head = compound_head(page);
1426

1427
		if (!page_cache_get_speculative(head))
1428 1429 1430
			goto pte_unmap;

		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
1431
			put_page(head);
1432 1433 1434
			goto pte_unmap;
		}

1435
		VM_BUG_ON_PAGE(compound_head(page) != head, page);
1436 1437

		SetPageReferenced(page);
1438 1439 1440 1441 1442 1443 1444 1445
		pages[*nr] = page;
		(*nr)++;

	} while (ptep++, addr += PAGE_SIZE, addr != end);

	ret = 1;

pte_unmap:
1446 1447
	if (pgmap)
		put_dev_pagemap(pgmap);
1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466
	pte_unmap(ptem);
	return ret;
}
#else

/*
 * If we can't determine whether or not a pte is special, then fail immediately
 * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
 * to be special.
 *
 * For a futex to be placed on a THP tail page, get_futex_key requires a
 * __get_user_pages_fast implementation that can pin pages. Thus it's still
 * useful to have gup_huge_pmd even if we can't operate on ptes.
 */
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
			 int write, struct page **pages, int *nr)
{
	return 0;
}
1467
#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
1468

1469
#if defined(__HAVE_ARCH_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489
static int __gup_device_huge(unsigned long pfn, unsigned long addr,
		unsigned long end, struct page **pages, int *nr)
{
	int nr_start = *nr;
	struct dev_pagemap *pgmap = NULL;

	do {
		struct page *page = pfn_to_page(pfn);

		pgmap = get_dev_pagemap(pfn, pgmap);
		if (unlikely(!pgmap)) {
			undo_dev_pagemap(nr, nr_start, pages);
			return 0;
		}
		SetPageReferenced(page);
		pages[*nr] = page;
		get_page(page);
		(*nr)++;
		pfn++;
	} while (addr += PAGE_SIZE, addr != end);
1490 1491 1492

	if (pgmap)
		put_dev_pagemap(pgmap);
1493 1494 1495
	return 1;
}

1496
static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1497 1498 1499
		unsigned long end, struct page **pages, int *nr)
{
	unsigned long fault_pfn;
1500 1501 1502 1503 1504
	int nr_start = *nr;

	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
		return 0;
1505

1506 1507 1508 1509 1510
	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
		undo_dev_pagemap(nr, nr_start, pages);
		return 0;
	}
	return 1;
1511 1512
}

1513
static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
1514 1515 1516
		unsigned long end, struct page **pages, int *nr)
{
	unsigned long fault_pfn;
1517 1518 1519 1520 1521
	int nr_start = *nr;

	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
		return 0;
1522

1523 1524 1525 1526 1527
	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
		undo_dev_pagemap(nr, nr_start, pages);
		return 0;
	}
	return 1;
1528 1529
}
#else
1530
static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1531 1532 1533 1534 1535 1536
		unsigned long end, struct page **pages, int *nr)
{
	BUILD_BUG();
	return 0;
}

1537
static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
1538 1539 1540 1541 1542 1543 1544
		unsigned long end, struct page **pages, int *nr)
{
	BUILD_BUG();
	return 0;
}
#endif

1545 1546 1547
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
		unsigned long end, int write, struct page **pages, int *nr)
{
1548
	struct page *head, *page;
1549 1550
	int refs;

1551
	if (!pmd_access_permitted(orig, write))
1552 1553
		return 0;

1554
	if (pmd_devmap(orig))
1555
		return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
1556

1557
	refs = 0;
1558
	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
1559 1560 1561 1562 1563 1564 1565
	do {
		pages[*nr] = page;
		(*nr)++;
		page++;
		refs++;
	} while (addr += PAGE_SIZE, addr != end);

1566
	head = compound_head(pmd_page(orig));
1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578
	if (!page_cache_add_speculative(head, refs)) {
		*nr -= refs;
		return 0;
	}

	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
		*nr -= refs;
		while (refs--)
			put_page(head);
		return 0;
	}

1579
	SetPageReferenced(head);
1580 1581 1582 1583 1584 1585
	return 1;
}

static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
		unsigned long end, int write, struct page **pages, int *nr)
{
1586
	struct page *head, *page;
1587 1588
	int refs;

1589
	if (!pud_access_permitted(orig, write))
1590 1591
		return 0;

1592
	if (pud_devmap(orig))
1593
		return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
1594

1595
	refs = 0;
1596
	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
1597 1598 1599 1600 1601 1602 1603
	do {
		pages[*nr] = page;
		(*nr)++;
		page++;
		refs++;
	} while (addr += PAGE_SIZE, addr != end);

1604
	head = compound_head(pud_page(orig));
1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616
	if (!page_cache_add_speculative(head, refs)) {
		*nr -= refs;
		return 0;
	}

	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
		*nr -= refs;
		while (refs--)
			put_page(head);
		return 0;
	}

1617
	SetPageReferenced(head);
1618 1619 1620
	return 1;
}

1621 1622 1623 1624 1625
static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
			unsigned long end, int write,
			struct page **pages, int *nr)
{
	int refs;
1626
	struct page *head, *page;
1627

1628
	if (!pgd_access_permitted(orig, write))
1629 1630
		return 0;

1631
	BUILD_BUG_ON(pgd_devmap(orig));
1632
	refs = 0;
1633
	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
1634 1635 1636 1637 1638 1639 1640
	do {
		pages[*nr] = page;
		(*nr)++;
		page++;
		refs++;
	} while (addr += PAGE_SIZE, addr != end);

1641
	head = compound_head(pgd_page(orig));
1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653
	if (!page_cache_add_speculative(head, refs)) {
		*nr -= refs;
		return 0;
	}

	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
		*nr -= refs;
		while (refs--)
			put_page(head);
		return 0;
	}

1654
	SetPageReferenced(head);
1655 1656 1657
	return 1;
}

1658 1659 1660 1661 1662 1663 1664 1665
static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
		int write, struct page **pages, int *nr)
{
	unsigned long next;
	pmd_t *pmdp;

	pmdp = pmd_offset(&pud, addr);
	do {
1666
		pmd_t pmd = READ_ONCE(*pmdp);
1667 1668

		next = pmd_addr_end(addr, end);
1669
		if (!pmd_present(pmd))
1670 1671 1672 1673 1674 1675 1676 1677
			return 0;

		if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) {
			/*
			 * NUMA hinting faults need to be handled in the GUP
			 * slowpath for accounting purposes and so that they
			 * can be serialised against THP migration.
			 */
1678
			if (pmd_protnone(pmd))
1679 1680 1681 1682 1683 1684
				return 0;

			if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
				pages, nr))
				return 0;

1685 1686 1687 1688 1689 1690 1691 1692
		} else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
			/*
			 * architecture have different format for hugetlbfs
			 * pmd format and THP pmd format
			 */
			if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
					 PMD_SHIFT, next, write, pages, nr))
				return 0;
1693
		} else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
1694
			return 0;
1695 1696 1697 1698 1699
	} while (pmdp++, addr = next, addr != end);

	return 1;
}

1700
static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end,
1701
			 int write, struct page **pages, int *nr)
1702 1703 1704 1705
{
	unsigned long next;
	pud_t *pudp;

1706
	pudp = pud_offset(&p4d, addr);
1707
	do {
1708
		pud_t pud = READ_ONCE(*pudp);
1709 1710 1711 1712

		next = pud_addr_end(addr, end);
		if (pud_none(pud))
			return 0;
1713
		if (unlikely(pud_huge(pud))) {
1714
			if (!gup_huge_pud(pud, pudp, addr, next, write,
1715 1716 1717 1718 1719
					  pages, nr))
				return 0;
		} else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
			if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
					 PUD_SHIFT, next, write, pages, nr))
1720 1721 1722 1723 1724 1725 1726 1727
				return 0;
		} else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
			return 0;
	} while (pudp++, addr = next, addr != end);

	return 1;
}

1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745
static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end,
			 int write, struct page **pages, int *nr)
{
	unsigned long next;
	p4d_t *p4dp;

	p4dp = p4d_offset(&pgd, addr);
	do {
		p4d_t p4d = READ_ONCE(*p4dp);

		next = p4d_addr_end(addr, end);
		if (p4d_none(p4d))
			return 0;
		BUILD_BUG_ON(p4d_huge(p4d));
		if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
			if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
					 P4D_SHIFT, next, write, pages, nr))
				return 0;
1746
		} else if (!gup_pud_range(p4d, addr, next, write, pages, nr))
1747 1748 1749 1750 1751 1752
			return 0;
	} while (p4dp++, addr = next, addr != end);

	return 1;
}

1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793
static void gup_pgd_range(unsigned long addr, unsigned long end,
		int write, struct page **pages, int *nr)
{
	unsigned long next;
	pgd_t *pgdp;

	pgdp = pgd_offset(current->mm, addr);
	do {
		pgd_t pgd = READ_ONCE(*pgdp);

		next = pgd_addr_end(addr, end);
		if (pgd_none(pgd))
			return;
		if (unlikely(pgd_huge(pgd))) {
			if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
					  pages, nr))
				return;
		} else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
			if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
					 PGDIR_SHIFT, next, write, pages, nr))
				return;
		} else if (!gup_p4d_range(pgd, addr, next, write, pages, nr))
			return;
	} while (pgdp++, addr = next, addr != end);
}

#ifndef gup_fast_permitted
/*
 * Check if it's allowed to use __get_user_pages_fast() for the range, or
 * we need to fall back to the slow version:
 */
bool gup_fast_permitted(unsigned long start, int nr_pages, int write)
{
	unsigned long len, end;

	len = (unsigned long) nr_pages << PAGE_SHIFT;
	end = start + len;
	return end >= start;
}
#endif

1794 1795
/*
 * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
1796 1797 1798
 * the regular GUP.
 * Note a difference with get_user_pages_fast: this always returns the
 * number of pages pinned, 0 if no pages were pinned.
1799 1800 1801 1802
 */
int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
			  struct page **pages)
{
1803
	unsigned long len, end;
1804
	unsigned long flags;
1805 1806 1807 1808 1809 1810 1811
	int nr = 0;

	start &= PAGE_MASK;
	len = (unsigned long) nr_pages << PAGE_SHIFT;
	end = start + len;

	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
1812
					(void __user *)start, len)))
1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826
		return 0;

	/*
	 * Disable interrupts.  We use the nested form as we can already have
	 * interrupts disabled by get_futex_key.
	 *
	 * With interrupts disabled, we block page table pages from being
	 * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
	 * for more details.
	 *
	 * We do not adopt an rcu_read_lock(.) here as we also want to
	 * block IPIs that come from THPs splitting.
	 */

1827 1828
	if (gup_fast_permitted(start, nr_pages, write)) {
		local_irq_save(flags);
1829
		gup_pgd_range(start, end, write, pages, &nr);
1830 1831
		local_irq_restore(flags);
	}
1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854

	return nr;
}

/**
 * get_user_pages_fast() - pin user pages in memory
 * @start:	starting user address
 * @nr_pages:	number of pages from start to pin
 * @write:	whether pages will be written to
 * @pages:	array that receives pointers to the pages pinned.
 *		Should be at least nr_pages long.
 *
 * Attempt to pin user pages in memory without taking mm->mmap_sem.
 * If not successful, it will fall back to taking the lock and
 * calling get_user_pages().
 *
 * 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.
 */
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
			struct page **pages)
{
1855
	unsigned long addr, len, end;
1856
	int nr = 0, ret = 0;
1857 1858

	start &= PAGE_MASK;
1859 1860 1861 1862
	addr = start;
	len = (unsigned long) nr_pages << PAGE_SHIFT;
	end = start + len;

1863 1864 1865
	if (nr_pages <= 0)
		return 0;

1866 1867
	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
					(void __user *)start, len)))
1868
		return -EFAULT;
1869 1870

	if (gup_fast_permitted(start, nr_pages, write)) {
1871 1872 1873
		local_irq_disable();
		gup_pgd_range(addr, end, write, pages, &nr);
		local_irq_enable();
1874 1875
		ret = nr;
	}
1876 1877 1878 1879 1880 1881

	if (nr < nr_pages) {
		/* Try to get the remaining pages with get_user_pages */
		start += nr << PAGE_SHIFT;
		pages += nr;

1882 1883
		ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
				write ? FOLL_WRITE : 0);
1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896

		/* Have to be a bit careful with return values */
		if (nr > 0) {
			if (ret < 0)
				ret = nr;
			else
				ret += nr;
		}
	}

	return ret;
}

1897
#endif /* CONFIG_HAVE_GENERIC_GUP */