mm: save soft-dirty bits on file pages

Andy reported that if file page get reclaimed we lose the soft-dirty bit
if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get
encoded into pte entry.  Thus when #pf happens on such non-present pte
we can restore it back.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 87da3590c61e..5bff08147768 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -57,17 +57,22 @@ static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
                 unsigned long addr, unsigned long pgoff, pgprot_t prot)
 {
         int err = -ENOMEM;
-        pte_t *pte;
+        pte_t *pte, ptfile;
         spinlock_t *ptl;
 
         pte = get_locked_pte(mm, addr, &ptl);
         if (!pte)
                 goto out;
 
-        if (!pte_none(*pte))
+        ptfile = pgoff_to_pte(pgoff);
+
+        if (!pte_none(*pte)) {
+                if (pte_present(*pte) && pte_soft_dirty(*pte))
+                        pte_file_mksoft_dirty(ptfile);
                 zap_pte(mm, vma, addr, pte);
+        }
 
-        set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
+        set_pte_at(mm, addr, pte, ptfile);
         /*
          * We don't need to run update_mmu_cache() here because the "file pte"
          * being installed by install_file_pte() is not a real pte - it's a