Re: [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach_group()

Jacob Pan
2020-07-15T15:54:40Z

On Wed, 15 Jul 2020 08:47:36 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:

> Hi Jacob,
>
> On 7/15/20 12:39 AM, Jacob Pan wrote:
> > On Tue, 14 Jul 2020 13:57:01 +0800
> > Lu Baolu<baolu.lu@linux.intel.com> wrote:
> >
> >> This adds two new aux-domain APIs for a use case like vfio/mdev
> >> where sub-devices derived from an aux-domain capable device are
> >> created and put in an iommu_group.
> >>
> >> /**
> >> * iommu_aux_attach_group - attach an aux-domain to an iommu_group
> >> which
> >> * contains sub-devices (for example
> >> mdevs) derived
> >> * from @dev.
> >> * @domain: an aux-domain;
> >> * @group: an iommu_group which contains sub-devices derived from
> >> @dev;
> >> * @dev: the physical device which supports IOMMU_DEV_FEAT_AUX.
> >> *
> >> * Returns 0 on success, or an error value.
> >> */
> >> int iommu_aux_attach_group(struct iommu_domain *domain,
> >> struct iommu_group *group,
> >> struct device *dev)
> >>
> >> /**
> >> * iommu_aux_detach_group - detach an aux-domain from an
> >> iommu_group *
> >> * @domain: an aux-domain;
> >> * @group: an iommu_group which contains sub-devices derived from
> >> @dev;
> >> * @dev: the physical device which supports IOMMU_DEV_FEAT_AUX.
> >> *
> >> * @domain must have been attached to @group via
> >> iommu_aux_attach_group(). */
> >> void iommu_aux_detach_group(struct iommu_domain *domain,
> >> struct iommu_group *group,
> >> struct device *dev)
> >>
> >> It also adds a flag in the iommu_group data structure to identify
> >> an iommu_group with aux-domain attached from those normal ones.
> >>
> >> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
> >> ---
> >> drivers/iommu/iommu.c | 58
> >> +++++++++++++++++++++++++++++++++++++++++++ include/linux/iommu.h |
> >> 17 +++++++++++++ 2 files changed, 75 insertions(+)
> >>
> >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> >> index e1fdd3531d65..cad5a19ebf22 100644
> >> --- a/drivers/iommu/iommu.c
> >> +++ b/drivers/iommu/iommu.c
> >> @@ -45,6 +45,7 @@ struct iommu_group {
> >> struct iommu_domain *default_domain;
> >> struct iommu_domain *domain;
> >> struct list_head entry;
> >> + unsigned int aux_domain_attached:1;
> >> };
> >>
> >> struct group_device {
> >> @@ -2759,6 +2760,63 @@ int iommu_aux_get_pasid(struct iommu_domain
> >> *domain, struct device *dev) }
> >> EXPORT_SYMBOL_GPL(iommu_aux_get_pasid);
> >>
> >> +/**
> >> + * iommu_aux_attach_group - attach an aux-domain to an iommu_group
> >> which
> >> + * contains sub-devices (for example
> >> mdevs) derived
> >> + * from @dev.
> >> + * @domain: an aux-domain;
> >> + * @group: an iommu_group which contains sub-devices derived from
> >> @dev;
> >> + * @dev: the physical device which supports IOMMU_DEV_FEAT_AUX.
> >> + *
> >> + * Returns 0 on success, or an error value.
> >> + */
> >> +int iommu_aux_attach_group(struct iommu_domain *domain,
> >> + struct iommu_group *group, struct
> >> device *dev) +{
> >> + int ret = -EBUSY;
> >> +
> >> + mutex_lock(&group->mutex);
> >> + if (group->domain)
> >> + goto out_unlock;
> >> +
> > Perhaps I missed something but are we assuming only one mdev per
> > mdev group? That seems to change the logic where vfio does:
> > iommu_group_for_each_dev()
> > iommu_aux_attach_device()
> >
>
> It has been changed in PATCH 4/4:
>
> static int vfio_iommu_attach_group(struct vfio_domain *domain,
> struct vfio_group *group)
> {
> if (group->mdev_group)
> return iommu_aux_attach_group(domain->domain,
> group->iommu_group,
> group->iommu_device);
> else
> return iommu_attach_group(domain->domain,
> group->iommu_group);
> }
>
> So, for both normal domain and aux-domain, we use the same concept:
> attach a domain to a group.
>
I get that, but don't you have to attach all the devices within the
group? Here you see the group already has a domain and exit.

> Best regards,
> baolu

[Jacob Pan]