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

Nicolin Chen
2023-05-19T19:34:25Z

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