[PATCH 32/70] mm/THP: use pmd_populate() to update the pmd with pgtable_t pointer

From: Luis Henriques
Date: Tue Jun 04 2013 - 10:19:25 EST -stable review patch. If anyone has any objections, please let me know.


From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>

commit 7c3425123ddfdc5f48e7913ff59d908789712b18 upstream.

We should not use set_pmd_at to update pmd_t with pgtable_t pointer.
set_pmd_at is used to set pmd with huge pte entries and architectures
like ppc64, clear few flags from the pte when saving a new entry.
Without this change we observe bad pte errors like below on ppc64 with
THP enabled.

BUG: Bad page map in process ld mm=0xc000001ee39f4780 pte:7fc3f37848000001 pmd:c000001ec0000000

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ luis: adjust context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
mm/huge_memory.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 57c4b93..7d0eb9e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1955,7 +1955,12 @@ static void collapse_huge_page(struct mm_struct *mm,
- set_pmd_at(mm, address, pmd, _pmd);
+ /*
+ * We can only use set_pmd_at when establishing
+ * hugepmds and never for establishing regular pmds that
+ * points to regular pagetables. Use pmd_populate for that
+ */
+ pmd_populate(mm, pmd, pmd_pgtable(_pmd));
goto out;

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