linux-kernel - [PATCH 3.12 052/142] powerpc/thp: Add write barrier after updating the valid bit

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Message-Id: <4cd682a176e4972805bc10ad04a95642daa6d3dd.1411724724.git.jslaby@suse.cz>
Date:	Fri, 26 Sep 2014 11:44:23 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 052/142] powerpc/thp: Add write barrier after updating the valid bit

From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...ux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/powerpc/mm/hugepage-hash64.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/hugepage-hash64.c b/arch/powerpc/mm/hugepage-hash64.c
index 34de9e0cdc34..f50c4dfd1819 100644
--- a/arch/powerpc/mm/hugepage-hash64.c
+++ b/arch/powerpc/mm/hugepage-hash64.c
@@ -168,8 +168,11 @@ 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;
 }
-- 
2.1.0

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