mm: migration: do not lose soft dirty bit if page is in migration state

If page migration is turned on in config and the page is migrating, we
may lose the soft dirty bit.  If fork and mprotect are called on
migrating pages (once migration is complete) pages do not obtain the
soft dirty bit in the correspond pte entries.  Fix it adding an
appropriate test on swap entries.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Andy Lutomirski <luto@amacapital.net>
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: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 94722a4d6b43..a3af058f68e4 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -94,13 +94,16 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                         swp_entry_t entry = pte_to_swp_entry(oldpte);
 
                         if (is_write_migration_entry(entry)) {
+                                pte_t newpte;
                                 /*
                                  * A protection check is difficult so
                                  * just be safe and disable write
                                  */
                                 make_migration_entry_read(&entry);
-                                set_pte_at(mm, addr, pte,
-                                        swp_entry_to_pte(entry));
+                                newpte = swp_entry_to_pte(entry);
+                                if (pte_swp_soft_dirty(oldpte))
+                                        newpte = pte_swp_mksoft_dirty(newpte);
+                                set_pte_at(mm, addr, pte, newpte);
                         }
                         pages++;
                 }