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

From: Alex Williamson
Sent: Wednesday, September 1, 2021 12:16 AM

On Mon, 30 Aug 2021 19:59:10 -0700
Nicolin Chen [off-list ref] wrote:

quoted

The SMMUv3 devices implemented in the Grace SoC support NVIDIA's

custom

quoted

CMDQ-Virtualization (CMDQV) hardware. Like the new ECMDQ feature first
introduced in the ARM SMMUv3.3 specification, CMDQV adds multiple

VCMDQ

quoted

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/

quoted

* PATCH-9 and PATCH-10 are to accommodate the NVIDIA implementation

with

quoted

  the existing arm-smmu-v3 driver.

* PATCH-11 borrows the "implementation infrastructure" from the arm-

smmu

quoted

  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()

quoted

 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

+++++++++++++++++

quoted

 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

quoted

 create mode 100644 drivers/iommu/arm/arm-smmu-v3/nvidia-smmu-v3.c

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