On Wed, Sep 01, 2021 at 06:55:55AM +0000, Tian, Kevin wrote: > > From: Alex Williamson > > Sent: Wednesday, September 1, 2021 12:16 AM > > > > On Mon, 30 Aug 2021 19:59:10 -0700 > > Nicolin Chen <nicolinc@xxxxxxxxxx> wrote: > > > > > The SMMUv3 devices implemented in the Grace SoC support NVIDIA's > > custom > > > CMDQ-Virtualization (CMDQV) hardware. Like the new ECMDQ feature first > > > introduced in the ARM SMMUv3.3 specification, CMDQV adds multiple > > VCMDQ > > > interfaces to supplement the single architected SMMU_CMDQ in an effort > > > to reduce contention. > > > > > > This series of patches add CMDQV support with its preparational changes: > > > > > > * PATCH-1 to PATCH-8 are related to shared VMID feature: they are used > > > first to improve TLB utilization, second to bind a shared VMID with a > > > VCMDQ interface for hardware configuring requirement. > > > > The vfio changes would need to be implemented in alignment with the > > /dev/iommu proposals[1]. AIUI, the VMID is essentially binding > > multiple containers together for TLB invalidation, which I expect in > > the proposal below is largely already taken care of in that a single > > iommu-fd can support multiple I/O address spaces and it's largely > > expected that a hypervisor would use a single iommu-fd so this explicit > > connection by userspace across containers wouldn't be necessary. > > Agree. VMID is equivalent to DID (domain id) in other vendor iommus. > with /dev/iommu multiple I/O address spaces can share the same VMID > via nesting. No need of exposing VMID to userspace to build the > connection. Indeed, this looks like a flavour of the accelerated invalidation stuff we've talked about already. I would see it probably exposed as some HW specific IOCTL on the iommu fd to get access to the accelerated invalidation for IOASID's in the FD. Indeed, this seems like a further example of why /dev/iommu is looking like a good idea as this RFC is very complicated to do something fairly simple. Where are thing on the /dev/iommu work these days? Thanks, Jason
