> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Tuesday, March 30, 2021 12:32 AM > > On Wed, Mar 24, 2021 at 12:05:28PM -0700, Jacob Pan wrote: > > > > IMHO a use created PASID is either bound to a mm (current) at creation > > > time, or it will never be bound to a mm and its page table is under > > > user control via /dev/ioasid. > > > > > True for PASID used in native SVA bind. But for binding with a guest mm, > > PASID is allocated first (VT-d virtual cmd interface Spec 10.4.44), the > > bind with the host IOMMU when vIOMMU PASID cache is invalidated. > > > > Our intention is to have two separate interfaces: > > 1. /dev/ioasid (allocation/free only) > > 2. /dev/sva (handles all SVA related activities including page tables) > > I'm not sure I understand why you'd want to have two things. Doesn't > that just complicate everything? > > Manipulating the ioasid, including filling it with page tables, seems > an integral inseperable part of the whole interface. Why have two ? Hi, Jason, Actually above is a major open while we are refactoring vSVA uAPI toward this direction. We have two concerns about merging /dev/ioasid with /dev/sva, and would like to hear your thought whether they are valid. First, userspace may use ioasid in a non-SVA scenario where ioasid is bound to specific security context (e.g. a control vq in vDPA) instead of tying to mm. In this case there is no pgtable binding initiated from user space. Instead, ioasid is allocated from /dev/ioasid and then programmed to the intended security context through specific passthrough framework which manages that context. Second, ioasid is managed per process/VM while pgtable binding is a device-wise operation. The userspace flow looks like below for an integral /dev/ioasid interface: -----------initialization---------- - ioctl(container->fd, VFIO_SET_IOMMU, VFIO_TYPE1_NESTING_IOMMU) - ioasid_fd = open(/dev/ioasid) - ioctl(ioasid_fd, IOASID_GET_USVA_FD, &sva_fd) //an empty context - ioctl(device->fd, VFIO_DEVICE_SET_SVA, &sva_fd); //sva_fd ties to device - ioctl(sva_fd, USVA_GET_INFO, &sva_info); -----------runtime---------------- - ioctl(ioasid_fd, IOMMU_ALLOC_IOASID, &ioasid); - ioctl(sva_fd, USVA_BIND_PGTBL, &bind_data); - ioctl(sva_fd, USVA_FLUSH_CACHE, &inv_info); - ioctl(sva_fd, USVA_UNBIND_PGTBL, &unbind_data); -----------destroy---------------- - ioctl(device->fd, VFIO_DEVICE_UNSET_SVA, &sva_fd); - close(sva_fd) - close(ioasid_fd) Our hesitation here is based on one of your earlier comments that you are not a fan of constructing fd's through ioctl. Are you OK with above flow or have a better idea of handling it? With separate interfaces then userspace just opens /dev/sva instead of getting it through ioasid_fd: - ioasid_fd = open(/dev/ioasid) - sva_fd = open(/dev/sva) Thanks Kevin
