From: Alex Williamson <alex.williamson@redhat.com>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>,
Robin Murphy <robin.murphy@arm.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
Cornelia Huck <cohuck@redhat.com>,
Kevin Tian <kevin.tian@intel.com>,
Ashok Raj <ashok.raj@intel.com>,
Dave Jiang <dave.jiang@intel.com>, Liu Yi L <yi.l.liu@intel.com>,
iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org
Subject: Re: [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev()
Date: Fri, 31 Jul 2020 12:14:18 -0600 [thread overview]
Message-ID: <20200731121418.0274afb8@x1.home> (raw)
In-Reply-To: <06fd91c1-a978-d526-7e2b-fec619a458e4@linux.intel.com>
On Fri, 31 Jul 2020 14:30:03 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:
> Hi Alex,
>
> On 2020/7/30 4:25, Alex Williamson wrote:
> > 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.
>
> Agreed. Given that a group may contain both non-aux and aux devices,
> adding such flag in iommu_group doesn't make sense.
>
> >
> > 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
> > resolve the jump from a domain to an aux-domain just as well as adding
> > this separate iommu_aux_get_domain_for_dev() interface. The is_aux
> > test might also be useful in other cases too.
>
> Let's rehearsal our use case.
>
> unsigned long pasid;
> struct iommu_domain *domain;
> struct device *dev = mdev_dev(mdev);
> struct device *iommu_device = vfio_mdev_get_iommu_device(dev);
>
> [1] domain = iommu_get_domain_for_dev(dev);
> if (!domain)
> return -ENODEV;
>
> [2] pasid = iommu_aux_get_pasid(domain, iommu_device);
> if (pasid <= 0)
> return -EINVAL;
>
> /* Program the device context */
> ....
>
> The reason why I add this iommu_aux_get_domain_for_dev() is that we need
> to make sure the domain got at [1] is valid to be used at [2].
>
> https://lore.kernel.org/linux-iommu/20200707150408.474d81f1@x1.home/
Yep, I thought that was a bit of a leap in logic.
> When calling into iommu_aux_get_pasid(), the iommu driver should make
> sure that @domain is a valid aux-domain for @iommu_device. Hence, for
> our use case, it seems that there's no need for a is_aux_domain() api.
>
> Anyway, I'm not against adding a new is_aux_domain() api if there's a
> need elsewhere.
I think it could work either way, we could have an
iommu_get_aux_domain_for_dev() which returns NULL if the domain is not
an aux domain, or we could use iommu_get_domain_for_dev() and the
caller could test the domain with iommu_is_aux_domain() if they need to
confirm if it's an aux domain. The former could even be written using
the latter, a wrapper of iommu_get_domain_for_dev() that checks aux
property before returning. Thanks,
Alex
next prev parent reply other threads:[~2020-07-31 18:14 UTC|newest]
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
2020-07-31 6:30 ` Lu Baolu
2020-07-31 18:14 ` Alex Williamson [this message]
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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