mm: softdirty: addresses before VMAs in PTE holes aren't softdirty

In PTE holes that contain VM_SOFTDIRTY VMAs, unmapped addresses before
VM_SOFTDIRTY VMAs are reported as softdirty by /proc/pid/pagemap.  This
bug was introduced in commit 68b5a6524856 ("mm: softdirty: respect
VM_SOFTDIRTY in PTE holes").  That commit made /proc/pid/pagemap look at
VM_SOFTDIRTY in PTE holes but neglected to observe the start of VMAs
returned by find_vma.

Tested:
  Wrote a selftest that creates a PMD-sized VMA then unmaps the first
  page and asserts that the page is not softdirty. I'm going to send the
  pagemap selftest in a later commit.

Signed-off-by: Peter Feiner <pfeiner@google.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Jamie Liu <jamieliu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 9 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index dfc791c42d64..c34156888d70 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -931,23 +931,32 @@ static int pagemap_pte_hole(unsigned long start, unsigned long end,
         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;
+                /* End of address space hole, which we mark as non-present. */
+                unsigned long hole_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);
+                if (vma)
+                        hole_end = min(end, vma->vm_start);
+                else
+                        hole_end = end;
+
+                for (; addr < hole_end; addr += PAGE_SIZE) {
+                        err = add_to_pagemap(addr, &pme, pm);
+                        if (err)
+                                goto out;
                 }
 
-                for (; addr < vm_end; addr += PAGE_SIZE) {
+                if (!vma)
+                        break;
+
+                /* Addresses in the VMA. */
+                if (vma->vm_flags & VM_SOFTDIRTY)
+                        pme.pme |= PM_STATUS2(pm->v2, __PM_SOFT_DIRTY);
+                for (; addr < min(end, vma->vm_end); addr += PAGE_SIZE) {
                         err = add_to_pagemap(addr, &pme, pm);
                         if (err)
                                 goto out;
                 }
         }
-
 out:
         return err;
 }