Re: [PATCH v8 3/3] iommu/arm-smmu-v3: Enable CFGI/TLBI-repeat workaround on Tegra264

[Ashish Mhetre <amhetre@nvidia.com>]

On 7/23/2026 12:46 AM, Nicolin Chen wrote:
> On Wed, Jul 22, 2026 at 10:20:33AM +0000, Ashish Mhetre wrote:
>> The host repeats only the invalidations it issues itself. On a nesting
>> setup the guest submits its own invalidations, either directly through
>> VCMDQ or via the iommufd user-invalidation path, so the guest is the one
>> that has to apply the workaround there. Report the erratum to user space
>> through the new IOMMU_HW_INFO_ARM_SMMUV3_ERRATA_REPEAT_TLBI_CFGI hw_info
>> flag so a VMM can confirm the guest runs a matching "nvidia,tegra264-smmu"
>> (or otherwise double the commands itself). The host therefore does not
>> repeat the guest's user-issued invalidations, which would otherwise be
>> doubled a second time.
> I think this "enable" patch is doing a bit too much.
>
> All the iommufd-related changes can be added separately
>
> I would do a cleanup:
>   - arm-smmu-v3: Factor force_sync
>   - arm-smmu-v3: Add arm_smmu_erratum_repeat_tlbi_cfgi_key and WAR
>   - arm-smmu-v3-iommufd: Add IOMMU_HW_INFO_ARM_SMMUV3_ERRATA_REPEAT_TLBI_CFGI
>   - arm-smmu-v3: Set arm_smmu_erratum_repeat_tlbi_cfgi_key
>    

Okay, I will add one more patch to series for iommu-fd related changes 
in v9.

>> +/**
>> + * enum iommu_hw_info_arm_smmuv3_flags - Flags for ARM SMMUv3 hw_info
>> + * @IOMMU_HW_INFO_ARM_SMMUV3_ERRATA_REPEAT_TLBI_CFGI: If set, user space must
>> + *	issue TLBI/CFGI+SYNC commands twice due to a hardware erratum T264-SMMU-3.
>> + *	See the description at arm_smmu_erratum_repeat_tlbi_cfgi_key.
> You can follow the kdoc style as enum iommufd_option.
>
> Nicolin

Ack, I will fix it in v9.

Thanks,
Ashish Mhetre