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    SubjectRe: [PATCH 1/1] iommu/arm-smmu-v3: eliminate a potential memory corruption on Hi16xx soc
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    On 15/10/2018 09:36, Zhen Lei wrote:
    > ITS translation register map:
    > 0x0000-0x003C Reserved
    > 0x0040 GITS_TRANSLATER
    > 0x0044-0xFFFC Reserved
    >

    Can you add a better opening than the ITS translation register map?

    > 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

    I think arm_smmu_device.sync_count is better, or "sync_count member in
    the the smmu driver control struct".

    > luckly that the previous and the next neighbour of "sync_count" are both aligned

    /s/luckly/luckily or fortunately/

    > 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 <thunder.leizhen@huawei.com>
    > ---
    > 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 */

    I think that a more detailed comment is required.

    > u32 sync_count;

    Can you indent these 2 members? However - as discussed internally - this
    may have endian issue so better to declare full 64b struct.

    > + } __attribute__((aligned(8)));
    >
    > /* IOMMU core code handle */
    > struct iommu_device iommu;
    >
    Thanks



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