iommu/arm-smmu-v3: Use WRITE_ONCE() when changing validity of an STE

[ 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 <jean-philippe@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 7bd9858..48d3820 100644 (file)
--- 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 */