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

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, May 17, 2023 at 11:08:12AM +0800, Liu, Jingqi wrote:

> > +     /*
> > +      * All drivers support IOMMU_HWPT_TYPE_DEFAULT, so pass it through.
> > +      * For any other hwpt_type, check the ops->domain_alloc_user_data_len
> > +      * presence and its result.
> > +      */
> > +     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;
> > +             }
> Would it be better if the later check "klen" is moved here ?
>     if (klen) {
>                 [...]
>     }
> If this check fails here, there's no need to execute the code after it.
> If this path is not executed, "klen" is 0, and there's no need to check it.
> Do I understand it right ?

Makes sense. And the klen value isn't really being used. So,
we may likely change it to a bool one. Also, I'm thinking of
forcing a !!cmd->data_len for a non-DEFAULT hwpt_type:

+	if (cmd->hwpt_type != IOMMU_HWPT_TYPE_DEFAULT) {
+		if (!cmd->data_len) {
+			rc = -EINVAL;
+			goto out_put_pt;
+		}
+		if (!ops->domain_alloc_user_data_len) {
+			rc = -EOPNOTSUPP;
+			goto out_put_pt;
+		}
+		if (!ops->hwpt_type_is_supported(cmd->hwpt_type)) {
+			rc = -EINVAL;
+			goto out_put_pt;
+		}

Then, for the latter part, simply:
+	if (cmd->data_len) {
+		// malloc data
+	}

Thanks
Nic