Hi Jason, On Fri, 10 Dec 2021 08:31:09 -0400, Jason Gunthorpe <j...@nvidia.com> wrote:
> On Fri, Dec 10, 2021 at 09:06:24AM +0000, Jean-Philippe Brucker wrote: > > On Thu, Dec 09, 2021 at 10:14:04AM -0800, Jacob Pan wrote: > > > > This looks like we're just one step away from device drivers needing > > > > multiple PASIDs for kernel DMA so I'm trying to figure out how to > > > > evolve the API towards that. It's probably as simple as keeping a > > > > kernel IOASID set at first, but then we'll probably want to > > > > optimize by having multiple overlapping sets for each device driver > > > > (all separate from the SVA set). > > > Sounds reasonable to start with a kernel set for in-kernel DMA once > > > we need multiple ones. But I am not sure what *overlapping* sets mean > > > here, could you explain? > > > > Given that each device uses a separate PASID table, we could allocate > > the same set of PASID values for different device drivers. We just need > > to make sure that those values are different from PASIDs allocated for > > user SVA. > > Why does user SVA need global values anyhow? > Currently, we have mm.pasid for user SVA. mm is global. We could have per device PASID for dedicated devices (not shared across mm's), but that would make things a lot more complex. I am thinking multiple PASIDs per mm is needed, right? For VT-d, the shared workqueue (SWQ) requires global PASIDs in that we cannot have two processes use the same PASID to submit work on a workqueue shared by the two processes. Each process's PASID must be unique to the SWQ's PASID table. > Jason Thanks, Jacob _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
