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? 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. 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? It maybe somewhat reasonable that some devices could have some easy 'make a SVA PASID on current' interface built in, 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. > 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 ? What is the set used for? 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? Jason
