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    SubjectRe: [PATCH v11 05/13] iommu: Add attach/detach_dev_pasid iommu interface
    On Wed, Aug 17, 2022 at 09:20:16AM +0800, Lu Baolu wrote:

    > +static int __iommu_set_group_pasid(struct iommu_domain *domain,
    > + struct iommu_group *group, ioasid_t pasid)
    > +{
    > + struct iommu_domain *ops_domain;
    > + struct group_device *device;
    > + int ret = 0;
    > +
    > + if (domain == group->blocking_domain)
    > + ops_domain = xa_load(&group->pasid_array, pasid);
    > + else
    > + ops_domain = domain;

    This seems weird, why isn't this just always

    domain->ops->set_dev_pasid()?

    > + if (curr) {
    > + ret = xa_err(curr) ? : -EBUSY;
    > + goto out_unlock;
    > + }
    > +
    > + ret = __iommu_set_group_pasid(domain, group, pasid);
    > + if (ret) {
    > + __iommu_set_group_pasid(group->blocking_domain, group, pasid);
    > + xa_erase(&group->pasid_array, pasid);

    I was looking at this trying to figure out why we are having
    attach/detach semantics vs set and this error handling seems to be the
    reason

    Lets add a comment because it is subtle thing:

    Setting a PASID to a blocking domain cannot fail, so we can always
    safely error unwind a failure to attach a domain back to the original
    group configuration of the PASID being unused.

    > +/*
    > + * iommu_detach_device_pasid() - Detach the domain from pasid of device
    > + * @domain: the iommu domain.
    > + * @dev: the attached device.
    > + * @pasid: the pasid of the device.
    > + *
    > + * The @domain must have been attached to @pasid of the @dev with
    > + * iommu_attach_device_pasid().
    > + */
    > +void iommu_detach_device_pasid(struct iommu_domain *domain, struct device *dev,
    > + ioasid_t pasid)

    Don't pass domain here?

    > +/*
    > + * iommu_get_domain_for_dev_pasid() - Retrieve domain for @pasid of @dev
    > + * @dev: the queried device
    > + * @pasid: the pasid of the device
    > + *
    > + * This is a variant of iommu_get_domain_for_dev(). It returns the existing
    > + * domain attached to pasid of a device. It's only for internal use of the
    > + * IOMMU subsystem. The caller must take care to avoid any possible
    > + * use-after-free case.

    How exactly does the caller manage that?

    > + *
    > + * Return: attached domain on success, NULL otherwise.
    > + */
    > +struct iommu_domain *
    > +iommu_get_domain_for_dev_pasid(struct device *dev, ioasid_t pasid)
    > +{
    > + struct iommu_domain *domain;
    > + struct iommu_group *group;
    > +
    > + if (!pasid_valid(pasid))
    > + return NULL;

    Why bother? If the pasid is not valid then it definitely won't be in the xarray.

    But otherwise this overall thing seems fine to me

    Jason

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