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17 Apr 2020 08:22:44 -0700 Date: Fri, 17 Apr 2020 08:28:39 -0700 From: Jacob Pan To: Auger Eric Subject: Re: [PATCH v11 05/10] iommu/vt-d: Add bind guest PASID support Message-ID: <20200417082839.45d6321e@jacob-builder> In-Reply-To: <2025736d-e7f2-d746-e030-e609b2f465e2@redhat.com> References: <1585939334-21396-1-git-send-email-jacob.jun.pan@linux.intel.com> <1585939334-21396-6-git-send-email-jacob.jun.pan@linux.intel.com> <20200410124557.4012b99b@jacob-builder> <6d9721a8-2198-5ecd-6c8b-fc43ff2ad7e1@redhat.com> <2025736d-e7f2-d746-e030-e609b2f465e2@redhat.com> Organization: OTC X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Cc: Yi L , "Tian, Kevin" , "Raj, Ashok" , Jean-Philippe Brucker , LKML , "iommu@lists.linux-foundation.org" , Alex Williamson , David Woodhouse , Jonathan Cameron X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Fri, 17 Apr 2020 09:46:55 +0200 Auger Eric 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. > Thanks > > Eric > > > >> > >> Besides, the comment is a bit misleading as it gives the > >> impression it is only true for mdev and there is no associated > >> check. > > > > Thanks > > Kevin > > > [Jacob Pan] _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu