Hi Jason, On Mon, 22 Mar 2021 09:03:00 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Fri, Mar 19, 2021 at 11:22:21AM -0700, Jacob Pan wrote: > > Hi Jason, > > > > On Fri, 19 Mar 2021 10:54:32 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx> > > wrote: > > > On Fri, Mar 19, 2021 at 02:41:32PM +0100, Jean-Philippe Brucker > > > wrote: > > > > On Fri, Mar 19, 2021 at 09:46:45AM -0300, Jason Gunthorpe wrote: > > > > > On Fri, Mar 19, 2021 at 10:58:41AM +0100, Jean-Philippe Brucker > > > > > wrote: > > > > > > Although there is no use for it at the moment (only two upstream > > > > > > users and it looks like amdkfd always uses current too), I quite > > > > > > like the client-server model where the privileged process does > > > > > > bind() and programs the hardware queue on behalf of the client > > > > > > process. > > > > > > > > > > This creates a lot complexity, how do does process A get a secure > > > > > reference to B? How does it access the memory in B to setup the > > > > > HW? > > > > > > > > mm_access() for example, and passing addresses via IPC > > > > > > I'd rather the source process establish its own PASID and then pass > > > the rights to use it to some other process via FD passing than try to > > > go the other way. There are lots of security questions with something > > > like mm_access. > > > > > > > Thank you all for the input, it sounds like we are OK to remove mm > > argument from iommu_sva_bind_device() and iommu_sva_alloc_pasid() for > > now? > > > > Let me try to summarize PASID allocation as below: > > > > Interfaces | Usage | Limit | bind¹ |User visible > > /dev/ioasid² | G-SVA/IOVA | cgroup | No > > |Yes char dev³ | SVA | cgroup | > > Yes |No iommu driver | default PASID| no > > | No |No kernel | super SVA | no > > | yes |No > > > > ¹ Allocated during SVA bind > > ² PASIDs allocated via /dev/ioasid are not bound to any mm. But its > > ownership is assigned to the process that does the allocation. > > What does "not bound to a mm" mean? > I meant, the IOASID allocated via /dev/ioasid is in a clean state (just a number). It's initial state is not bound to an mm. Unlike, sva_bind_device() where the IOASID is allocated during bind time. The use case is to support guest SVA bind, where allocation and bind are in two separate steps. > 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 thought the whole point of something like a /dev/ioasid was to get > away from each and every device creating its own PASID interface? > yes, but only for the use cases that need to expose PASID to the userspace. AFAICT, the cases are: 1. guest SVA (bind guest mm) 2. full PF/VF assignment(not mediated) where guest driver want to program the actual PASID onto the device. > It maybe somewhat reasonable that some devices could have some easy > 'make a SVA PASID on current' interface built in, I agree, this is the case PASID is hidden from the userspace, right? e.g. uacce. > but anything more > complicated should use /dev/ioasid, and anything consuming PASID > should also have an API to import and attach a PASID from /dev/ioasid. > Would the above two use cases constitute the "complicated" criteria? Or we should say anything that need the explicit PASID value has to through /dev/ioasid? Could you give some highlevel hint on the APIs that hook up IOASID allocated from /dev/ioasid and use cases that combine device and domain information? Yi is working on /dev/sva RFC, it would be good to have a direction check. > > Currently, the proposed /dev/ioasid interface does not map individual > > PASID with an FD. The FD is at the ioasid_set granularity and bond to > > the current mm. We could extend the IOCTLs to cover individual PASID-FD > > passing case when use cases arise. Would this work? > > Is it a good idea that the FD is per ioasid_set ? We were thinking the allocation IOCTL is on a per set basis, then we know the ownership of between PASIDs and its set. If per PASID FD is needed, we can extend. > What is the set used > for? > I tried to document the concept in https://lore.kernel.org/lkml/1614463286-97618-2-git-send-email-jacob.jun.pan@xxxxxxxxxxxxxxx/ In terms of usage for guest SVA, an ioasid_set is mostly tied to a host mm, the use case is as the following: 1. Identify a pool of PASIDs for permission checking (below to the same VM), e.g. only allow SVA binding for PASIDs allocated from the same set. 2. Allow different PASID-aware kernel subsystems to associate, e.g. KVM, device drivers, and IOMMU driver. i.e. each KVM instance only cares about the ioasid_set associated with the VM. Events notifications are also within the ioasid_set to synchronize PASID states. 3. Guest-Host PASID look up (each set has its own XArray to store the mapping) 4. Quota control (going away once we have cgroup) > Usually kernel interfaces work nicer with a one fd/one object model. > > But even if it is a set, you could pass the set between co-operating > processes and the PASID can be created in the correct 'current'. But > there is all kinds of security questsions as soon as you start doing > anything like this - is there really a use case? > We don't see a use case for passing ioasid_set to another process. All the four use cases above are for the current process. > Jason Thanks, Jacob
