From: Will Deacon <will@kernel.org>
Date: Wed, 15 Jan 2020 15:21:47 +0000
Subject: iommu/arm-smmu-v3: Use WRITE_ONCE() when changing validity of an STE
Git-commit: d71e01716b3606a6648df7e5646ae12c75babde4
Patch-mainline: v5.6-rc1
References: bsc#1175713

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 <jean-philippe@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 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 c2d1325c9d39..3aa6538d85e2 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1873,7 +1873,8 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
 						 STRTAB_STE_1_EATS_TRANS));
 
 	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 */