Re: [PATCH v7 1/9] iommu/arm-smmu-v3: Handle ARM erratum for CONT under invalidation with SVA

[Pranjal Shrivastava <praan@google.com>]

On Mon, Sep 21, 2026 at 08:55:09PM -0300, Jason Gunthorpe wrote:
> The erratum (MMU-700: #3777127, S3: #3673557) deals with under
> invalidation of a CONT PTE grouping in the SMMU. The recommended work
> around is to use a range invalidation that spans the entire CONT. The only
> user of CONT in the kernel right now is through SVA sharing a CPU page
> table that contains a CONT created by the mm.
> 
> Previously it was thought that this errata was dealt with because the
> driver always uses range invalidation. However, there is a subtle detail
> in the errata that the invalidation range must fully enclose the entire
> CONT for it to work.
> 
> It seems that two sequential range invalidations, with a split point
> falling inside a CONT grouping, will not prevent the errata.
> 
> The SMMU's range invalidation generation algorithm does not produce a
> single invalidation for a single SVA invalidation request, nor does the mm
> carefully align the SVA invalidation ranges to accommodate the splitting
> of the invalidation into several ranges.
> 
> Thus, when processing a SVA invalidation, the range invalidation splitting
> routine can generate a range invalidation that is split in the middle of
> the CONT and risk under invalidation from this errata. This condition
> could be triggered by a malicious userspace manipulating the TLB gathers
> via mmap/mprotect/munmap.
> 
> Update the errata list to the include the S3 variation, detect the IOMMUs
> that have it, and then have SVA invalidations use a simplified version of
> the over invalidation algorithm from the tlbi rework series. This ensures
> that a single range invalidation is issued for a single MMU notifier
> callback and now the range invalidation is guarenteed to cover any posible
> CONT.
> 
> Future work to add CONT to iommu_domain page tables should either use this
> one-invalidate/one-range invalidation algorithm or disable CONT support in
> the iommu_domain.
> 
> Cc: stable@vger.kernel.org
> Cc: Vijayanand Jitta <vijayanand.jitta@oss.qualcomm.com>
> Fixes: 3f1ce8e85ee0 ("iommu/arm-smmu-v3: Share process page tables")
> Reviewed-by: Mostafa Saleh <smostafa@google.com>
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  Documentation/arch/arm64/silicon-errata.rst   |  3 +-
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |  7 ++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 91 +++++++++++++++----
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h   |  5 +
>  4 files changed, 88 insertions(+), 18 deletions(-)
> 

Reviewed-by: Pranjal Shrivastava <peaan@google.com>

Thanks,
Praan