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. > PASID is about constructing an arbitary DMA IOVA map for PCI-E > devices, being able to intercept device DMA faults, etc. > An arbitrary IOVA map does not need PASID. In IOVA, you do map/unmap explicitly, why you need to handle IO page fault? To me, PASID identifies an address space that is associated with a mm_struct. > SVA is doing DMA IOVA 1:1 with the mm_struct CPU VA. DMA faults > trigger the same thing as CPU page faults. If is it not 1:1 then there > is no "shared". When SVA is done using PCI-E PASID it is "PASID for > SVA". Lots of existing devices already have SVA without PASID or > IOMMU, so lets not muddy the terminology. > I agree. This conversation is about "PASID for SVA" not "SVA without PASID" > vPASID/vIOMMU is allowing a guest to control the DMA IOVA map and > manipulate the PASIDs. > > vSVA is when a guest uses a vPASID to provide SVA, not sure this is > an informative term. > I agree. > This particular patch series seems to be about vPASID/vIOMMU for > vfio-mdev vs the other vPASID/vIOMMU patch which was about vPASID for > vfio-pci. > Yi can correct me but this set is is about VFIO-PCI, VFIO-mdev will be introduced later. > > > > If so, I don't see the need for userspace to know there is a > > > > PASID. All user space need is that my current mm is bound to a > > > > device by the driver. So it can be a one-step process for user > > > > instead of two. > > > > > > You've missed the entire point of the conversation, VDPA already > > > needs more than "my current mm is bound to a device" > > > > You mean current version of vDPA? or a potential future version of > > vDPA? > > Future VDPA drivers, it was made clear this was important to Intel > during the argument about VDPA as a mdev. > > Jason Thanks, Jacob
