Re: [PATCH v6 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

Jason Gunthorpe
2025-11-26T18:36:52Z

On Tue, Nov 25, 2025 at 05:10:09PM -0800, Nicolin Chen wrote:
> When a master is attached from an old domain to a new domain, it needs to
> build an invalidation array to delete and add the array entries from/onto
> the invalidation arrays of those two domains, passed via the to_merge and
> to_unref arguments into arm_smmu_invs_merge/unref() respectively.
>
> Since the master->num_streams might differ across masters, a memory would
> have to be allocated when building an to_merge/to_unref array which might
> fail with -ENOMEM.
>
> On the other hand, an attachment to arm_smmu_blocked_domain must not fail
> so it's the best to avoid any memory allocation in that path.
>
> Pre-allocate a fixed size invalidation array for every master. This array
> will be used as a scratch to fill dynamically when building a to_merge or
> to_unref invs array. Sort fwspec->ids in an ascending order to fit to the
> arm_smmu_invs_merge() function.
>
> Co-developed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 8 ++++
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 41 +++++++++++++++++++--
> 2 files changed, 45 insertions(+), 4 deletions(-)

Looks good and addresses Will's remark

Jason