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Re: [RFC v6 00/24] vSMMUv3/pSMMUv3 2 stage VFIO integration

From: Zhangfei Gao
Subject: Re: [RFC v6 00/24] vSMMUv3/pSMMUv3 2 stage VFIO integration
Date: Tue, 31 Mar 2020 16:24:20 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0

Hi, Eric

On 2020/3/31 下午4:12, Auger Eric wrote:
Hi Zhangfei,

On 3/31/20 8:42 AM, Zhangfei Gao wrote:
Hi, Eric

On 2020/3/21 上午12:58, Eric Auger wrote:
Up to now vSMMUv3 has not been integrated with VFIO. VFIO
integration requires to program the physical IOMMU consistently
with the guest mappings. However, as opposed to VTD, SMMUv3 has
no "Caching Mode" which allows easy trapping of guest mappings.
This means the vSMMUV3 cannot use the same VFIO integration as VTD.

However SMMUv3 has 2 translation stages. This was devised with
virtualization use case in mind where stage 1 is "owned" by the
guest whereas the host uses stage 2 for VM isolation.

This series sets up this nested translation stage. It only works
if there is one physical SMMUv3 used along with QEMU vSMMUv3 (in
other words, it does not work if there is a physical SMMUv2).

- We force the host to use stage 2 instead of stage 1, when we
    detect a vSMMUV3 is behind a VFIO device. For a VFIO device
    without any virtual IOMMU, we still use stage 1 as many existing
    SMMUs expect this behavior.
- We use PCIPASIDOps to propage guest stage1 config changes on
    STE (Stream Table Entry) changes.
- We implement a specific UNMAP notifier that conveys guest
    IOTLB invalidations to the host
- We register MSI IOVA/GPA bindings to the host so that this latter
    can build a nested stage translation
- As the legacy MAP notifier is not called anymore, we must make
    sure stage 2 mappings are set. This is achieved through another
    prereg memory listener.
- Physical SMMU stage 1 related faults are reported to the guest
    via en eventfd mechanism and exposed trhough a dedicated VFIO-PCI
    region. Then they are reinjected into the guest.

Best Regards


This series can be found at:

Kernel Dependencies:
[1] [PATCH v10 00/11] SMMUv3 Nested Stage Setup (VFIO part)
[2] [PATCH v10 00/13] SMMUv3 Nested Stage Setup (IOMMU part)
branch at:
Really appreciated that you re-start this work.

I tested your branch and some update.

Guest: https://github.com/Linaro/linux-kernel-warpdrive/tree/sva-devel
qemu: https://github.com/eauger/qemu/tree/v4.2.0-2stage-rfcv6

The guest I am using is contains Jean's sva patches.
Since currently they are many patch conflict, so use two different tree.

No-sva mode works.
This mode, guest directly get physical address via ioctl.
OK thanks for testing
While vSVA can not work, there are still much work to do.
I am trying to SVA mode, and it fails, so choose no-sva instead.
iommu_dev_enable_feature(parent, IOMMU_DEV_FEAT_SVA)
Indeed I assume there are plenty of things missing to make vSVM work on
ARM (iommu, vfio, QEMU). I am currently reviewing Jacob and Yi's kernel
and QEMU series on Intel side. After that, I will come back to you to
help. Also vSMMUv3 does not support multiple contexts at the moment. I
will add this soon.

Still the problem I have is testing. Any suggestion welcome.

To make sure
Do you mean you need a environment for testing?

How about Hisilicon kunpeng920, arm64 platform supporting SVA in host now.
There is such a platform in linaro mlab that I think we can share.
Currently I am testing with uacce,
By testing a user driver (hisi zip accelerator) in guest, we can test vSVA and PASID easily.


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