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Subject[PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc
ITS translation register map:
0x0000-0x003C Reserved
0x0044-0xFFFC Reserved

The standard GITS_TRANSLATER register in ITS is only 4 bytes, but Hisilicon
expands the next 4 bytes to carry some IMPDEF information. That means, 8 bytes
data will be written to MSIAddress each time.

MSIAddr: |----4bytes----|----4bytes----|
| MSIData | IMPDEF |

There is no problem for ITS, because the next 4 bytes space is reserved in ITS.
But it will overwrite the 4 bytes memory following "sync_count". It's very
luckly that the previous and the next neighbour of "sync_count" are both aligned
by 8 bytes, so no problem is met now.

It's good to explicitly add a workaround:
1. Add gcc __attribute__((aligned(8))) to make sure that "sync_count" is always
aligned by 8 bytes.
2. Add a "u64" union member to make sure the 4 bytes padding is always exist.

There is no functional change.

Signed-off-by: Zhen Lei <>
drivers/iommu/arm-smmu-v3.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 5059d09..a07bc0d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -586,7 +586,10 @@ struct arm_smmu_device {

struct arm_smmu_strtab_cfg strtab_cfg;

+ union {
+ u64 padding; /* workaround for Hisilicon */
u32 sync_count;
+ } __attribute__((aligned(8)));

/* IOMMU core code handle */
struct iommu_device iommu;

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