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>
This commit is contained in:
Naoya Horiguchi 2015-02-11 15:28:06 -08:00 committed by Linus Torvalds
parent 6f4576e368
commit 48684a65b4
3 changed files with 19 additions and 8 deletions

View File

@ -806,6 +806,9 @@ static int clear_refs_test_walk(unsigned long start, unsigned long end,
struct clear_refs_private *cp = walk->private;
struct vm_area_struct *vma = walk->vma;
if (vma->vm_flags & VM_PFNMAP)
return 1;
/*
* Writing 1 to /proc/pid/clear_refs affects all pages.
* Writing 2 to /proc/pid/clear_refs only affects anonymous pages.

View File

@ -591,6 +591,9 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
unsigned long endvma = vma->vm_end;
unsigned long flags = qp->flags;
if (vma->vm_flags & VM_PFNMAP)
return 1;
if (endvma > end)
endvma = end;
if (vma->vm_start > start)

View File

@ -35,7 +35,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
do {
again:
next = pmd_addr_end(addr, end);
if (pmd_none(*pmd)) {
if (pmd_none(*pmd) || !walk->vma) {
if (walk->pte_hole)
err = walk->pte_hole(addr, next, walk);
if (err)
@ -165,9 +165,6 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
* or skip it via the returned value. Return 0 if we do walk over the
* current vma, and return 1 if we skip the vma. Negative values means
* error, where we abort the current walk.
*
* Default check (only VM_PFNMAP check for now) is used when the caller
* doesn't define test_walk() callback.
*/
static int walk_page_test(unsigned long start, unsigned long end,
struct mm_walk *walk)
@ -178,11 +175,19 @@ static int walk_page_test(unsigned long start, unsigned long end,
return walk->test_walk(start, end, walk);
/*
* Do not walk over vma(VM_PFNMAP), because we have no valid struct
* page backing a VM_PFNMAP range. See also commit a9ff785e4437.
* vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
* range, so we don't walk over it as we do for normal vmas. However,
* Some callers are interested in handling hole range and they don't
* want to just ignore any single address range. Such users certainly
* define their ->pte_hole() callbacks, so let's delegate them to handle
* vma(VM_PFNMAP).
*/
if (vma->vm_flags & VM_PFNMAP)
return 1;
if (vma->vm_flags & VM_PFNMAP) {
int err = 1;
if (walk->pte_hole)
err = walk->pte_hole(start, end, walk);
return err ? err : 1;
}
return 0;
}