Re: [PATCH v4 5/6] iommu/arm-smmu-v3-iommufd: Convert cache invalidation to the core array loop

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Jul 14, 2026 at 11:48:51AM -0700, Nicolin Chen wrote:
> arm_vsmmu_cache_invalidate() allocated a buffer for the entire user request
> array, walked the array converting each of the commands, and issued those
> converted commands to the cmdq in CMDQ_BATCH_ENTRIES sized chunks, carrying
> the sub-array bookkeeping all on its own.
> 
> The iommufd core now iterates the invalidation array and re-invokes the op
> with the not-yet-handled sub-array, so the driver only has to proceed with
> a single chunk per call.
> 
> Instead of a per-array allocation, use a fixed on-stack batch to copy from
> the userspace array. If the copy fails due to nonzero padding (VMM violates
> the ABI), fail the entire batch.
> 
> Convert the whole batch before issuing any of it: a malformed command is a
> userspace bug, so the first illegal command fails the batch as a unit,
> issuing nothing and leaving array->entry_num at zero, the same way the copy
> above bails on nonzero padding. A batch that converts cleanly is issued in
> full, so the op returns either a handled count with no error or zero with
> an error.
> 
> A zero-length array now returns success once the data type gets validated,
> matching the documented probe behavior, rather than the -EINVAL that the
> full-array copy helper would previously return.
> 
> This also fixes two long-standing bugs:
>  1) On a conversion failure the old code reported commands that it had
>     converted but not yet issued, so user space advanced its consumer
>     index past invalidations that never reached the cmdq.
>  2) A zero-length array was rejected with -EINVAL, although the uAPI
>     documents it as a valid request that only probes the data type.
> 
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Pranjal Shrivastava <praan@google.com>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  .../arm/arm-smmu-v3/arm-smmu-v3-iommufd.c     | 68 +++++++++++--------
>  1 file changed, 38 insertions(+), 30 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason