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' VM_SOFTDIRTY flag.
Signed-off-by: Peter Feiner <pfei...@google.com>
---
fs/proc/task_mmu.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index cfa63ee..dfc791c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -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)
- break;
+ 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;
+ }
}
+
+out:
return err;
}
--
2.0.0.526.g5318336
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