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

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.

CC: <stable@vger.kernel.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index 826893fcb3a78b0198d5fa4b0b047428d8852802..11f9a37ca2c6dda462caed6bb5a2d918644cbc2e 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;
 }