Re: [PATCH rfcv1 4/8] iommu/arm-smmu-v3: Introduce a per-domain arm_smmu_invs array

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Aug 13, 2025 at 06:25:35PM -0700, Nicolin Chen wrote:
> +/**
> + * arm_smmu_invs_del() - Remove @del_invs from @old_invs
> + * @old_invs: the old invalidation array
> + * @del_invs: an array of invlidations to delete
> + *
> + * Return: a newly allocated and sorted invalidation array on success, or an
> + * ERR_PTR.
> + *
> + * This function must be locked and serialized with arm_smmu_invs_add/dec(),
> + * but do not lockdep on any lock for KUNIT test.
> + *
> + * Caller is resposible for freeing the @old_invs and the returned one.
> + *
> + * Entries marked as trash will be completely removed in the returned array.
> + */
> +VISIBLE_IF_KUNIT
> +struct arm_smmu_invs *arm_smmu_invs_del(struct arm_smmu_invs *old_invs,
> +					struct arm_smmu_invs *del_invs)
> +{

Having looked at this more completely, I think we should drop this
function.

Just always do decr, then have a simple function to compact the list
after the decr:

struct arm_smmu_invs *arm_smmu_invs_cleanup(struct arm_smmu_invs *invs,
					    size_t to_del)
{
	struct arm_smmu_invs *new_invs;
	size_t i, j;

	if (WARN_ON(invs->num_invs < to_del))
		return NULL;

	new_invs = arm_smmu_invs_alloc(invs->num_invs - to_del);
	if (IS_ERR(new_invs))
		return NULL;

	for (i = 0, j = 0; i != invs->num_invs; i++) {
		if (!refcount_read(&invs->inv[i].users))
			continue;
		new_invs->inv[j] = invs->inv[i];
		j++;
	}
	return new_invs;
}

If this returns NULL then just leave the list alone, it is OK to sit
there with the 0 users left behind.

No need for the complex _del function and the _decr function..

This also means the memory doesn't need to be preallocated and it
significantly simplifies alot of the logic.

Jason