On Wed, Jul 21, 2021 at 02:13:23AM +0000, Tian, Kevin wrote: > > From: Shenming Lu > > Sent: Friday, July 16, 2021 8:20 PM > > > > On 2021/7/16 9:20, Tian, Kevin wrote: > > > To summarize, for vIOMMU we can work with the spec owner to > > > define a proper interface to feedback such restriction into the guest > > > if necessary. For the kernel part, it's clear that IOMMU fd should > > > disallow two devices attached to a single [RID] or [RID, PASID] slot > > > in the first place. > > > > > > Then the next question is how to communicate such restriction > > > to the userspace. It sounds like a group, but different in concept. > > > An iommu group describes the minimal isolation boundary thus all > > > devices in the group can be only assigned to a single user. But this > > > case is opposite - the two mdevs (both support ENQCMD submission) > > > with the same parent have problem when assigned to a single VM > > > (in this case vPASID is vm-wide translated thus a same pPASID will be > > > used cross both mdevs) while they instead work pretty well when > > > assigned to different VMs (completely different vPASID spaces thus > > > different pPASIDs). > > > > > > One thought is to have vfio device driver deal with it. In this proposal > > > it is the vfio device driver to define the PASID virtualization policy and > > > report it to userspace via VFIO_DEVICE_GET_INFO. The driver understands > > > the restriction thus could just hide the vPASID capability when the user > > > calls GET_INFO on the 2nd mdev in above scenario. In this way the > > > user even doesn't need to know such restriction at all and both mdevs > > > can be assigned to a single VM w/o any problem. > > > > > > > The restriction only probably happens when two mdevs are assigned to one > > VM, > > how could the vfio device driver get to know this info to accurately hide > > the vPASID capability for the 2nd mdev when VFIO_DEVICE_GET_INFO? > > There is no > > need to do this in other cases. > > > > I suppose the driver can detect it via whether two mdevs are opened by a > single process. Just have the kernel some ID for the PASID numberspace - devices with the same ID have to be represented as a single RID. Jason
