Hi Jason, On Wed, 16 Sep 2020 15:38:41 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Wed, Sep 16, 2020 at 11:21:10AM -0700, Jacob Pan (Jun) wrote: > > Hi Jason, > > On Wed, 16 Sep 2020 14:01:13 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx> > > wrote: > > > > > On Wed, Sep 16, 2020 at 09:33:43AM -0700, Raj, Ashok wrote: > > > > On Wed, Sep 16, 2020 at 12:07:54PM -0300, Jason Gunthorpe > > > > wrote: > > > > > On Tue, Sep 15, 2020 at 05:22:26PM -0700, Jacob Pan (Jun) > > > > > wrote: > > > > > > > If user space wants to bind page tables, create the PASID > > > > > > > with /dev/sva, use ioctls there to setup the page table > > > > > > > the way it wants, then pass the now configured PASID to a > > > > > > > driver that can use it. > > > > > > > > > > > > Are we talking about bare metal SVA? > > > > > > > > > > What a weird term. > > > > > > > > Glad you noticed it at v7 :-) > > > > > > > > Any suggestions on something less weird than > > > > Shared Virtual Addressing? There is a reason why we moved from > > > > SVM to SVA. > > > > > > SVA is fine, what is "bare metal" supposed to mean? > > > > > What I meant here is sharing virtual address between DMA and host > > process. This requires devices perform DMA request with PASID and > > use IOMMU first level/stage 1 page tables. > > This can be further divided into 1) user SVA 2) supervisor SVA > > (sharing init_mm) > > > > My point is that /dev/sva is not useful here since the driver can > > perform PASID allocation while doing SVA bind. > > No, you are thinking too small. > > Look at VDPA, it has a SVA uAPI. Some HW might use PASID for the SVA. > Could you point to me the SVA UAPI? I couldn't find it in the mainline. Seems VDPA uses VHOST interface? > When VDPA is used by DPDK it makes sense that the PASID will be SVA > and 1:1 with the mm_struct. > I still don't see why bare metal DPDK needs to get a handle of the PASID. Perhaps the SVA patch would explain. Or are you talking about vDPA DPDK process that is used to support virtio-net-pmd in the guest? > When VDPA is used by qemu it makes sense that the PASID will be an > arbitary IOVA map constructed to be 1:1 with the guest vCPU physical > map. /dev/sva allows a single uAPI to do this kind of setup, and qemu > can support it while supporting a range of SVA kernel drivers. VDPA > and vfio-mdev are obvious initial targets. > > *BOTH* are needed. > > In general any uAPI for PASID should have the option to use either the > mm_struct SVA PASID *OR* a PASID from /dev/sva. It costs virtually > nothing to implement this in the driver as PASID is just a number, and > gives so much more flexability. > Not really nothing in terms of PASID life cycles. For example, if user uses uacce interface to open an accelerator, it gets an FD_acc. Then it opens /dev/sva to allocate PASID then get another FD_pasid. Then we pass FD_pasid to the driver to bind page tables, perhaps multiple drivers. Now we have to worry about If FD_pasid gets closed before FD_acc(s) closed and all these race conditions. If we do not expose FD_pasid to the user, the teardown is much simpler and streamlined. Following each FD_acc close, PASID unbind is performed. > > Yi can correct me but this set is is about VFIO-PCI, VFIO-mdev will > > be introduced later. > > Last patch is: > > vfio/type1: Add vSVA support for IOMMU-backed mdevs > > So pretty hard to see how this is not about vfio-mdev, at least a > little.. > > Jason Thanks, Jacob
