Re: [PATCH v5 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

Nicolin Chen
2025-11-24T22:44:18Z

On Mon, Nov 24, 2025 at 09:42:55PM +0000, Will Deacon wrote:
> On Sat, Nov 08, 2025 at 12:08:05AM -0800, Nicolin Chen wrote:
> > + /* Put the ids into order for sorted to_merge/to_unref arrays */
> > + sort_nonatomic(fwspec->ids, fwspec->num_ids,
> > + sizeof(fwspec->ids[0]), arm_smmu_ids_cmp, NULL);
> > + /* ATS case adds num_ids of entries, on top of the base case */
> > + master->build_invs = arm_smmu_invs_alloc(2 + fwspec->num_ids);
>
> Although I can't point at a specific issue here, I'm nervous about mutating
> the 'fwspec->ids' array from within the driver, The array isn't allocated
> or populated directly by the driver and so I don't think we really have any
> business sorting it. Could we hack iommu_fwspec_add_ids() to keep the array
> ordered instead?

Yea, I think it makes sense to do it in the core, once we have the
data structure provided by the core as well.

Thanks
Nicolin