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mm: pagewalk: fix misbehavior of walk_page_range for vma(VM_PFNMAP)
walk_page_range() silently skips vma having VM_PFNMAP set, which leads to undesirable behaviour at client end (who called walk_page_range). For example for pagemap_read(), when no callbacks are called against VM_PFNMAP vma, pagemap_read() may prepare pagemap data for next virtual address range at wrong index. That could confuse and/or break userspace applications. This patch avoid this misbehavior caused by vma(VM_PFNMAP) like follows: - for pagemap_read() which has its own ->pte_hole(), call the ->pte_hole() over vma(VM_PFNMAP), - for clear_refs and queue_pages which have their own ->tests_walk, just return 1 and skip vma(VM_PFNMAP). This is no problem because these are not interested in hole regions, - for other callers, just skip the vma(VM_PFNMAP) as a default behavior. Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Signed-off-by: Shiraz Hashim <shashim@codeaurora.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -806,6 +806,9 @@ static int clear_refs_test_walk(unsigned long start, unsigned long end,
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struct clear_refs_private *cp = walk->private;
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struct vm_area_struct *vma = walk->vma;
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if (vma->vm_flags & VM_PFNMAP)
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return 1;
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/*
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* Writing 1 to /proc/pid/clear_refs affects all pages.
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* Writing 2 to /proc/pid/clear_refs only affects anonymous pages.
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@ -591,6 +591,9 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
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unsigned long endvma = vma->vm_end;
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unsigned long flags = qp->flags;
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if (vma->vm_flags & VM_PFNMAP)
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return 1;
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if (endvma > end)
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endvma = end;
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if (vma->vm_start > start)
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@ -35,7 +35,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
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do {
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again:
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next = pmd_addr_end(addr, end);
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if (pmd_none(*pmd)) {
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if (pmd_none(*pmd) || !walk->vma) {
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if (walk->pte_hole)
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err = walk->pte_hole(addr, next, walk);
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if (err)
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@ -165,9 +165,6 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
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* or skip it via the returned value. Return 0 if we do walk over the
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* current vma, and return 1 if we skip the vma. Negative values means
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* error, where we abort the current walk.
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*
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* Default check (only VM_PFNMAP check for now) is used when the caller
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* doesn't define test_walk() callback.
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*/
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static int walk_page_test(unsigned long start, unsigned long end,
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struct mm_walk *walk)
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@ -178,11 +175,19 @@ static int walk_page_test(unsigned long start, unsigned long end,
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return walk->test_walk(start, end, walk);
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/*
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* Do not walk over vma(VM_PFNMAP), because we have no valid struct
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* page backing a VM_PFNMAP range. See also commit a9ff785e4437.
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* vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
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* range, so we don't walk over it as we do for normal vmas. However,
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* Some callers are interested in handling hole range and they don't
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* want to just ignore any single address range. Such users certainly
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* define their ->pte_hole() callbacks, so let's delegate them to handle
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* vma(VM_PFNMAP).
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*/
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if (vma->vm_flags & VM_PFNMAP)
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return 1;
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if (vma->vm_flags & VM_PFNMAP) {
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int err = 1;
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if (walk->pte_hole)
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err = walk->pte_hole(start, end, walk);
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return err ? err : 1;
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}
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return 0;
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}
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