Re: [PATCH] iommu/arm-smmu-v3: Add HAFT support for SVA

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Jul 01, 2026 at 06:45:17PM +0100, Robin Murphy wrote:

> @@ -211,6 +213,9 @@ bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)
>  	if (system_supports_bbml2_noabort())
>  		feat_mask |= ARM_SMMU_FEAT_BBML2;
>  
> +	if (system_supports_haft())
> +		feat_mask |= ARM_SMMU_FEAT_HAFT;

I fear this is going to make SVA stop working on systems it currently
does work on, so it might be a major regression. 

SMMU HTTU is not a commonly implemented feature.. I think of all the
NVIDIA ARM chips only one supports it. Given that a quick internal
check is raising concerns this will be breaking for us. We need to
check in more detail which cores have HAFT.

Breaking already deployed SVA would be a major functional regression.

I think this should start by just enabling SMMU HAFT when CPU HAFT is
on, when possible. Maybe print a warning on the mismatch instead of
failing.

Since we can't break already deployed SVA a full solution would either
have to somehow turn off CPU HAFT or we ignore the gap in the AF
updates..

Jason