mm/THP: use pmd_populate() to update the pmd with pgtable_t pointer

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@linux.vnet.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
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, 6 insertions, 1 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 03a89a2f464b..362c329b83fe 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2325,7 +2325,12 @@ static void collapse_huge_page(struct mm_struct *mm,
                 pte_unmap(pte);
                 spin_lock(&mm->page_table_lock);
                 BUG_ON(!pmd_none(*pmd));
-                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));
                 spin_unlock(&mm->page_table_lock);
                 anon_vma_unlock_write(vma->anon_vma);
                 goto out;