Re: [PATCH rfcv1 5/8] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

Jason Gunthorpe
2025-08-26T19:56:48Z

On Wed, Aug 13, 2025 at 06:25:36PM -0700, Nicolin Chen wrote:
> @@ -3730,6 +3731,13 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
> return -ENOMEM;
> master->num_streams = fwspec->num_ids;
>
> + /* Max possible num_invs: two for ASID/VMIDs and num_ats for ATC_INVs */
> + master->invs = arm_smmu_invs_alloc(2 + num_ats);
> + if (IS_ERR(master->invs)) {
> + kfree(master->streams);
> + return PTR_ERR(master->invs);
> + }

This seems like a nice solution, but I would add a comment here that
it is locked by the group mutex, and check if ATS is supported:

/*
* Scratch memory to build the per-domain invalidation list. locked by
* the group_mutex. Max possible num_invs: two for ASID/VMIDs and
* num_streams for ATC_INVs
*/
if (dev_is_pci(master->dev) &&
pci_ats_supported(to_pci_dev(master->dev)))
master->invs = arm_smmu_invs_alloc(2 + master->num_streams);
else
master->invs = arm_smmu_invs_alloc(2);

And probably rename it scratch_invs or something to indicate it is
temporary memory.

I'm not sure there is any case where fwspec->num_ids >1 &&
ats_supported, or at least is should be really rare.

Jason