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

[Nicolin Chen]

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
  
> +/**
> + * 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