On Tue, Mar 30, 2021 at 01:37:05AM +0000, Tian, Kevin wrote: > > 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. This sounds like the exact opposite of what I'd like to see. I do not want to see every subsystem gaining APIs to program a PASID. All of that should be consolidated in *one place*. I do not want to see VDPA and VFIO have two nearly identical sets of APIs to control the PASID. Drivers consuming a PASID, like VDPA, should consume the PASID and do nothing more than authorize the HW to use it. quemu should have general code under the viommu driver that drives /dev/ioasid to create PASID's and manage the IO mapping according to the guest's needs. Drivers like VDPA and VFIO should simply accept that PASID and configure/authorize their HW to do DMA's with its tag. > 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: > > - 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); > - 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); > - 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? My reaction is to squash 'sva' and ioasid fds together, I can't see why you'd need two fds to manipulate a PASID. DEVICE_SET_SVA seems like the wrong language too, it should be more like DEVICE_ALLOW_IOASID which only tells the iommu and driver to alow the pci_device to use the IOASID. Jason
