powerpc/thp: Add write barrier after updating the valid bit

commit b0aa44a3dfae3d8f45bd1264349aa87f87b7774f upstream.

With hugepages, we store the hpte valid information in the pte page
whose address is stored in the second half of the PMD. Use a
write barrier to make sure clearing pmd busy bit and updating
hpte valid info are ordered properly.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index 826893f..11f9a37 100644 (file)
--- a/arch/powerpc/mm/hugepage-hash64.c
+++ b/arch/powerpc/mm/hugepage-hash64.c
@@ -172,8 +172,11 @@ repeat:
                mark_hpte_slot_valid(hpte_slot_array, index, slot);
        }
        /*
-        * No need to use ldarx/stdcx here
+        * The hpte valid is stored in the pgtable whose address is in the
+        * second half of the PMD. Order this against clearing of the busy bit in
+        * huge pmd.
         */
+       smp_wmb();
        *pmdp = __pmd(new_pmd & ~_PAGE_BUSY);
        return 0;
 }