Message-ID: <20210831101549.237151fa.alex.williamson@redhat.com>
Date:   Tue, 31 Aug 2021 10:15:49 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     <will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
        <cohuck@...hat.com>, <corbet@....net>, <nicoleotsuka@...il.com>,
        <vdumpa@...dia.com>, <thierry.reding@...il.com>,
        <linux-tegra@...r.kernel.org>, <nwatterson@...dia.com>,
        <Jonathan.Cameron@...wei.com>, <jean-philippe@...aro.org>,
        <song.bao.hua@...ilicon.com>, <eric.auger@...hat.com>,
        <thunder.leizhen@...wei.com>, <yuzenghui@...wei.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [RFC][PATCH v2 00/13] iommu/arm-smmu-v3: Add NVIDIA
 implementation

On Mon, 30 Aug 2021 19:59:10 -0700
Nicolin Chen <nicolinc@...dia.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.

We're expecting to talk more about the /dev/iommu approach at Plumbers
in few weeks.  Thanks,

Alex

[1]https://lore.kernel.org/kvm/BN9PR11MB5433B1E4AE5B0480369F97178C189@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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