RE: [PATCH v2 06/11] iommufd: IOMMU_HWPT_ALLOC allocation with user data

[Tian, Kevin]

> From: Yi Liu <yi.l.liu@xxxxxxxxx>
> Sent: Thursday, May 11, 2023 10:39 PM
> +	if (cmd->hwpt_type != IOMMU_HWPT_TYPE_DEFAULT) {
> +		if (!ops->domain_alloc_user_data_len) {
> +			rc = -EOPNOTSUPP;
> +			goto out_put_idev;
> +		}
> +		klen = ops->domain_alloc_user_data_len(cmd->hwpt_type);
> +		if (WARN_ON(klen < 0)) {
> +			rc = -EINVAL;
> +			goto out_put_pt;
> +		}
> +	}

What about passing the user pointer to the iommu driver which
then does the copy so we don't need an extra @data_len() 
callback for every driver?

> 
> +	switch (pt_obj->type) {
> +	case IOMMUFD_OBJ_IOAS:
> +		ioas = container_of(pt_obj, struct iommufd_ioas, obj);
> +		break;

this should fail if parent is specified.

> +	case IOMMUFD_OBJ_HW_PAGETABLE:
> +		/* pt_id points HWPT only when hwpt_type
> is !IOMMU_HWPT_TYPE_DEFAULT */
> +		if (cmd->hwpt_type == IOMMU_HWPT_TYPE_DEFAULT) {
> +			rc = -EINVAL;
> +			goto out_put_pt;
> +		}
> +
> +		parent = container_of(pt_obj, struct iommufd_hw_pagetable,
> obj);
> +		/*
> +		 * Cannot allocate user-managed hwpt linking to
> auto_created
> +		 * hwpt. If the parent hwpt is already a user-managed hwpt,
> +		 * don't allocate another user-managed hwpt linking to it.
> +		 */
> +		if (parent->auto_domain || parent->parent) {
> +			rc = -EINVAL;
> +			goto out_put_pt;
> +		}
> +		ioas = parent->ioas;

for nesting why is ioas required? In concept we can just pass NULL ioas
to iommufd_hw_pagetable_alloc() for this hwpt. If within that function
there is a need to toggle ioas for the parent it can always retrieve it
from the parent hwpt.