Messages in this thread | | | From | "Tian, Kevin" <> | Subject | RE: [PATCH v11 05/10] iommu/vt-d: Add bind guest PASID support | Date | Fri, 17 Apr 2020 23:46:13 +0000 |
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> From: Jacob Pan <jacob.jun.pan@linux.intel.com> > Sent: Friday, April 17, 2020 11:29 PM > > On Fri, 17 Apr 2020 09:46:55 +0200 > Auger Eric <eric.auger@redhat.com> wrote: > > > Hi Kevin, > > On 4/17/20 4:45 AM, Tian, Kevin wrote: > > >> From: Auger Eric > > >> Sent: Thursday, April 16, 2020 6:43 PM > > >> > > > [...] > > >>>>> + if (svm) { > > >>>>> + /* > > >>>>> + * If we found svm for the PASID, there must > > >>>>> be at > > >>>>> + * least one device bond, otherwise svm should > > >>>>> be freed. > > >>>>> + */ > > >>>>> + if (WARN_ON(list_empty(&svm->devs))) { > > >>>>> + ret = -EINVAL; > > >>>>> + goto out; > > >>>>> + } > > >>>>> + > > >>>>> + for_each_svm_dev(sdev, svm, dev) { > > >>>>> + /* In case of multiple sub-devices of > > >>>>> the same pdev > > >>>>> + * assigned, we should allow multiple > > >>>>> bind calls with > > >>>>> + * the same PASID and pdev. > > >>>>> + */ > > >>>>> + sdev->users++; > > >>>> What if this is not an mdev device. Is it also allowed? > > >>> Yes. IOMMU and VT-d driver is not mdev aware. Here mdev is just an > > >>> example of normal use case. You can bind the same PCI device (PF > > >>> or SRIOV VF) more than once to the same PASID. Just need to > > >>> unbind also. > > >> > > >> I don't get the point of binding a non mdev device several times > > >> with the same PASID. Do you intend to allow that at userspace > > >> level or prevent this from happening in VFIO? > > > > > > I feel it's better to prevent this from happening, otherwise VFIO > > > also needs to track the bind count and do multiple unbinds at > > > mm_exit. But it's not necessary to prevent it in VFIO. We can check > > > here upon whether aux_domain is valid, and if not return -EBUSY. > > Ah OK. So if we can detect the case here it is even better > > > I don't understand why VFIO cannot track, since it is mdev aware. if we > don;t refcount the users, one mdev unbind will result unbind for all > mdev under the same pdev. That may not be the right thing to do. >
The open here is not for mdev, which refcount is still required. Eric's point is for non-mdev endpoints. It's meaningless and not intuitive to allow binding a PASID multiple-times to the same device.
Thanks Kevin
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