linux-kernel - Re: [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach

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Date:   Wed, 15 Jul 2020 09:01:14 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, kvm@...r.kernel.org,
        Cornelia Huck <cohuck@...hat.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach_group()

On Wed, 15 Jul 2020 08:47:36 +0800
Lu Baolu <baolu.lu@...ux.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@...ux.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@...ux.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]