Commit 68b5a652 authored by Peter Feiner's avatar Peter Feiner Committed by Linus Torvalds
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mm: softdirty: respect VM_SOFTDIRTY in PTE holes

After a VMA is created with the VM_SOFTDIRTY flag set, /proc/pid/pagemap
should report that the VMA's virtual pages are soft-dirty until
VM_SOFTDIRTY is cleared (i.e., by the next write of "4" to
/proc/pid/clear_refs).  However, pagemap ignores the VM_SOFTDIRTY flag
for virtual addresses that fall in PTE holes (i.e., virtual addresses
that don't have a PMD, PUD, or PGD allocated yet).

To observe this bug, use mmap to create a VMA large enough such that
there's a good chance that the VMA will occupy an unused PMD, then test
the soft-dirty bit on its pages.  In practice, I found that a VMA that
covered a PMD's worth of address space was big enough.

This patch adds the necessary VMA lookup to the PTE hole callback in
/proc/pid/pagemap's page walk and sets soft-dirty according to the VMAs'
Signed-off-by: default avatarPeter Feiner <>
Acked-by: default avatarCyrill Gorcunov <>
Cc: Pavel Emelyanov <>
Cc: Hugh Dickins <>
Acked-by: default avatarNaoya Horiguchi <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 3a91053a
......@@ -925,15 +925,30 @@ static int pagemap_pte_hole(unsigned long start, unsigned long end,
struct mm_walk *walk)
struct pagemapread *pm = walk->private;
unsigned long addr;
unsigned long addr = start;
int err = 0;
pagemap_entry_t pme = make_pme(PM_NOT_PRESENT(pm->v2));
for (addr = start; addr < end; addr += PAGE_SIZE) {
err = add_to_pagemap(addr, &pme, pm);
if (err)
while (addr < end) {
struct vm_area_struct *vma = find_vma(walk->mm, addr);
pagemap_entry_t pme = make_pme(PM_NOT_PRESENT(pm->v2));
unsigned long vm_end;
if (!vma) {
vm_end = end;
} else {
vm_end = min(end, vma->vm_end);
if (vma->vm_flags & VM_SOFTDIRTY)
pme.pme |= PM_STATUS2(pm->v2, __PM_SOFT_DIRTY);
for (; addr < vm_end; addr += PAGE_SIZE) {
err = add_to_pagemap(addr, &pme, pm);
if (err)
goto out;
return err;
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