RE: [RFC][PATCH v2 00/13] iommu/arm-smmu-v3: Add NVIDIA implementation

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Alex Williamson
> Sent: Wednesday, September 1, 2021 12:16 AM
> 
> On Mon, 30 Aug 2021 19:59:10 -0700
> Nicolin Chen <nicolinc@nvidia.com> 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.

Thanks,
Kevin

> 
> We're expecting to talk more about the /dev/iommu approach at Plumbers
> in few weeks.  Thanks,
> 
> Alex
> 
> [1]https://lore.kernel.org/kvm/BN9PR11MB5433B1E4AE5B0480369F97178C1
> 89@BN9PR11MB5433.namprd11.prod.outlook.com/
> 
> 
> > * PATCH-9 and PATCH-10 are to accommodate the NVIDIA implementation
> with
> >   the existing arm-smmu-v3 driver.
> >
> > * PATCH-11 borrows the "implementation infrastructure" from the arm-
> smmu
> >   driver so later change can build upon it.
> >
> > * PATCH-12 adds an initial NVIDIA implementation related to host feature,
> >   and also adds implementation specific ->device_reset() and ->get_cmdq()
> >   callback functions.
> >
> > * PATCH-13 adds virtualization features using VFIO mdev interface, which
> >   allows user space hypervisor to map and get access to one of the VCMDQ
> >   interfaces of CMDQV module.
> >
> > ( Thinking that reviewers can get a better view of this implementation,
> >   I am attaching QEMU changes here for reference purpose:
> >       https://github.com/nicolinc/qemu/commits/dev/cmdqv_v6.0.0-rc2
> >   The branch has all preparational changes, while I'm still integrating
> >   device model and ARM-VIRT changes, and will push them these two days,
> >   although they might not be in a good shape of being sent to review yet )
> >
> > Above all, I marked RFC for this series, as I feel that we may come up
> > some better solution. So please kindly share your reviews and insights.
> >
> > Thank you!
> >
> > Changelog
> > v1->v2:
> >  * Added mdev interface support for hypervisor and VMs.
> >  * Added preparational changes for mdev interface implementation.
> >  * PATCH-12 Changed ->issue_cmdlist() to ->get_cmdq() for a better
> >    integration with recently merged ECMDQ-related changes.
> >
> > Nate Watterson (3):
> >   iommu/arm-smmu-v3: Add implementation infrastructure
> >   iommu/arm-smmu-v3: Add support for NVIDIA CMDQ-Virtualization hw
> >   iommu/nvidia-smmu-v3: Add mdev interface support
> >
> > Nicolin Chen (10):
> >   iommu: Add set_nesting_vmid/get_nesting_vmid functions
> >   vfio: add VFIO_IOMMU_GET_VMID and VFIO_IOMMU_SET_VMID
> >   vfio: Document VMID control for IOMMU Virtualization
> >   vfio: add set_vmid and get_vmid for vfio_iommu_type1
> >   vfio/type1: Implement set_vmid and get_vmid
> >   vfio/type1: Set/get VMID to/from iommu driver
> >   iommu/arm-smmu-v3: Add shared VMID support for NESTING
> >   iommu/arm-smmu-v3: Add VMID alloc/free helpers
> >   iommu/arm-smmu-v3: Pass dev pointer to arm_smmu_detach_dev
> >   iommu/arm-smmu-v3: Pass cmdq pointer in
> arm_smmu_cmdq_issue_cmdlist()
> >
> >  Documentation/driver-api/vfio.rst             |   34 +
> >  MAINTAINERS                                   |    2 +
> >  drivers/iommu/arm/arm-smmu-v3/Makefile        |    2 +-
> >  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-impl.c  |   15 +
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   |  121 +-
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h   |   18 +
> >  .../iommu/arm/arm-smmu-v3/nvidia-smmu-v3.c    | 1249
> +++++++++++++++++
> >  drivers/iommu/iommu.c                         |   20 +
> >  drivers/vfio/vfio.c                           |   25 +
> >  drivers/vfio/vfio_iommu_type1.c               |   37 +
> >  include/linux/iommu.h                         |    5 +
> >  include/linux/vfio.h                          |    2 +
> >  include/uapi/linux/vfio.h                     |   26 +
> >  13 files changed, 1537 insertions(+), 19 deletions(-)
> >  create mode 100644 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-
> impl.c
> >  create mode 100644 drivers/iommu/arm/arm-smmu-v3/nvidia-smmu-v3.c
> >
> 
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