Subject: [PATCH AUTOSEL 4.9 102/141] iommu/arm-smmu-v3: Use WRITE_ONCE() when changing validity of an STE

From: Sasha Levin <[email-masked]>
Date: Fri, 14 Feb 2020 11:20:42 -0500

From: Will Deacon <[email-masked]>

[ Upstream commit d71e01716b3606a6648df7e5646ae12c75babde4 ]

If, for some bizarre reason, the compiler decided to split up the write
of STE DWORD 0, we could end up making a partial structure valid.

Although this probably won't happen, follow the example of the
context-descriptor code and use WRITE_ONCE() to ensure atomicity of the
write.

Reported-by: Jean-Philippe Brucker <[email-masked]>
Signed-off-by: Will Deacon <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 drivers/iommu/arm-smmu-v3.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 7bd98585d78d2..48d3820087881 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1103,7 +1103,8 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_device *smmu, u32 sid,
 	}
 
 	arm_smmu_sync_ste_for_sid(smmu, sid);
-	dst[0] = cpu_to_le64(val);
+	/* See comment in arm_smmu_write_ctx_desc() */
+	WRITE_ONCE(dst[0], cpu_to_le64(val));
 	arm_smmu_sync_ste_for_sid(smmu, sid);
 
 	/* It's likely that we'll want to use the new STE soon */
-- 
2.20.1

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