[PATCH] powerpc: thp: Add write barrier after updating the valid bit

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

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 that 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>
---
 arch/powerpc/include/asm/pgtable-ppc64.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
index eb9261024f51..558beb760062 100644
--- a/arch/powerpc/include/asm/pgtable-ppc64.h
+++ b/arch/powerpc/include/asm/pgtable-ppc64.h
@@ -394,6 +394,12 @@ static inline void mark_hpte_slot_valid(unsigned char *hpte_slot_array,
 					unsigned int index, unsigned int hidx)
 {
 	hpte_slot_array[index] = hidx << 4 | 0x1 << 3;
+	/*
+	 * 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();
 }
 
 struct page *realmode_pfn_to_page(unsigned long pfn);
-- 
1.9.1