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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Cornelia Huck <cohuck@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Robin Murphy <robin.murphy@arm.com>
Subject: RE: [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev()
Date: Fri, 31 Jul 2020 02:17:35 +0000
Message-ID: <MWHPR11MB1645E578E14085A0E11A538A8C4E0@MWHPR11MB1645.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20200730141725.5f63b508@x1.home>

> From: Tian, Kevin
> Sent: Friday, July 31, 2020 8:26 AM
> 
> > From: Alex Williamson <alex.williamson@redhat.com>
> > Sent: Friday, July 31, 2020 4:17 AM
> >
> > On Wed, 29 Jul 2020 23:49:20 +0000
> > "Tian, Kevin" <kevin.tian@intel.com> wrote:
> >
> > > > From: Alex Williamson <alex.williamson@redhat.com>
> > > > Sent: Thursday, July 30, 2020 4:25 AM
> > > >
> > > > On Tue, 14 Jul 2020 13:57:02 +0800
> > > > Lu Baolu <baolu.lu@linux.intel.com> wrote:
> > > >
> > > > > The device driver needs an API to get its aux-domain. A typical usage
> > > > > scenario is:
> > > > >
> > > > >         unsigned long pasid;
> > > > >         struct iommu_domain *domain;
> > > > >         struct device *dev = mdev_dev(mdev);
> > > > >         struct device *iommu_device =
> vfio_mdev_get_iommu_device(dev);
> > > > >
> > > > >         domain = iommu_aux_get_domain_for_dev(dev);
> > > > >         if (!domain)
> > > > >                 return -ENODEV;
> > > > >
> > > > >         pasid = iommu_aux_get_pasid(domain, iommu_device);
> > > > >         if (pasid <= 0)
> > > > >                 return -EINVAL;
> > > > >
> > > > >          /* Program the device context */
> > > > >          ....
> > > > >
> > > > > This adds an API for such use case.
> > > > >
> > > > > Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> > > > > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> > > > > ---
> > > > >  drivers/iommu/iommu.c | 18 ++++++++++++++++++
> > > > >  include/linux/iommu.h |  7 +++++++
> > > > >  2 files changed, 25 insertions(+)
> > > > >
> > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > > > > index cad5a19ebf22..434bf42b6b9b 100644
> > > > > --- a/drivers/iommu/iommu.c
> > > > > +++ b/drivers/iommu/iommu.c
> > > > > @@ -2817,6 +2817,24 @@ void iommu_aux_detach_group(struct
> > > > iommu_domain *domain,
> > > > >  }
> > > > >  EXPORT_SYMBOL_GPL(iommu_aux_detach_group);
> > > > >
> > > > > +struct iommu_domain *iommu_aux_get_domain_for_dev(struct
> > device
> > > > *dev)
> > > > > +{
> > > > > +	struct iommu_domain *domain = NULL;
> > > > > +	struct iommu_group *group;
> > > > > +
> > > > > +	group = iommu_group_get(dev);
> > > > > +	if (!group)
> > > > > +		return NULL;
> > > > > +
> > > > > +	if (group->aux_domain_attached)
> > > > > +		domain = group->domain;
> > > >
> > > > Why wouldn't the aux domain flag be on the domain itself rather than
> > > > the group?  Then if we wanted sanity checking in patch 1/ we'd only
> > > > need to test the flag on the object we're provided.
> > > >
> > > > If we had such a flag, we could create an iommu_domain_is_aux()
> > > > function and then simply use iommu_get_domain_for_dev() and test
> that
> > > > it's an aux domain in the example use case.  It seems like that would
> > >
> > > IOMMU layer manages domains per parent device. Here given a
> >
> > Is this the IOMMU layer or the VT-d driver?  I don't see any notion of
> > managing domains relative to a parent in the IOMMU layer.  Please point
> > to something more specific if I'm wrong here.
> 
> it's maintained in VT-d driver (include/linux/intel-iommu.h)
> 
> struct device_domain_info {
>         struct list_head link;  /* link to domain siblings */
>         struct list_head global; /* link to global list */
>         struct list_head table; /* link to pasid table */
>         struct list_head auxiliary_domains; /* auxiliary domains
>                                              * attached to this device
>                                              */
> 	...
> 
> >
> > > dev (of mdev), we need a way to find its associated domain under its
> > > parent device. And we cannot simply use iommu_get_domain_for_dev
> > > on the parent device of the mdev, as it will give us the primary domain
> > > of parent device.
> >
> > Not the parent device of the mdev, but the mdev_dev(mdev) device.
> > Isn't that what this series is enabling, being able to return the
> > domain from the group that contains the mdev_dev?  We shouldn't need
> to
> > leave breadcrumbs on the group to know about the domain, the domain
> > itself should be the source of knowledge, or provide a mechanism/ops to
> > learn that knowledge.  Thanks,
> >
> > Alex
> 
> It's the tradeoff between leaving breadcrumb in domain or in group.
> Today the domain has no knowledge of mdev. It just includes a list
> of physical devices which are attached to the domain (either due to
> the device is assigned in a whole or as the parent device of an assigned
> mdev). Then we have two choices. One is to save the mdev_dev info
> in device_domain_info and maintain a mapping between mdev_dev
> and related aux domain. The other is to record the domain info directly
> in group. Earlier we choose the latter one as it looks simpler. If you
> prefer to the former one, we can think more and have a try.
> 

Please skip this comment. I have a wrong understanding of the problem
and is discussing with Baolu. He will reply with our conclusion later.

Thanks
Kevin
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  parent reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-14  5:56 [PATCH v3 0/4] iommu aux-domain APIs extensions Lu Baolu
2020-07-14  5:57 ` [PATCH v3 1/4] iommu: Check IOMMU_DEV_FEAT_AUX feature in aux api's Lu Baolu
2020-07-29 20:03   ` Alex Williamson
2020-07-30  1:46     ` Lu Baolu
2020-07-14  5:57 ` [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach_group() Lu Baolu
2020-07-14 16:39   ` Jacob Pan
2020-07-15  0:47     ` Lu Baolu
2020-07-15 16:01       ` Jacob Pan
2020-07-16  1:07         ` Lu Baolu
2020-07-29 20:03           ` Alex Williamson
2020-07-29 23:34             ` Tian, Kevin
2020-07-30 19:46               ` Alex Williamson
2020-07-31  5:47                 ` Lu Baolu
2020-07-31 18:05                   ` Alex Williamson
2020-08-03  1:57                     ` Lu Baolu
2020-07-14  5:57 ` [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev() Lu Baolu
2020-07-29 20:25   ` Alex Williamson
2020-07-29 23:49     ` Tian, Kevin
2020-07-30 20:17       ` Alex Williamson
2020-07-31  0:26         ` Tian, Kevin
2020-07-31  2:17         ` Tian, Kevin [this message]
2020-07-31  6:30     ` Lu Baolu
2020-07-31 18:14       ` Alex Williamson
2020-08-03  2:15         ` Lu Baolu
2020-07-14  5:57 ` [PATCH v3 4/4] vfio/type1: Use iommu_aux_at(de)tach_group() APIs Lu Baolu
2020-07-14  8:25   ` Christoph Hellwig
2020-07-14 16:29     ` Jacob Pan
2020-07-15  1:00       ` Lu Baolu
2020-07-15  1:23         ` Tian, Kevin
2020-07-29 20:32   ` Alex Williamson
2020-07-30  2:41     ` Lu Baolu
2020-07-30 21:17       ` Alex Williamson
2020-07-31  1:37         ` Lu Baolu
2020-07-30  9:36   ` Liu, Yi L
2020-07-31  1:39     ` Lu Baolu
2020-07-23 13:55 ` [PATCH v3 0/4] iommu aux-domain APIs extensions Lu Baolu

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