Re: [PATCH v7 00/10] mlx5 support for VFIO self test

[Alex Williamson <alex@shazbot.org>]

On Mon, 21 Sep 2026 19:35:40 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> Add an mlx5 driver to VFIO self test. This is largely a remix of the
> existing VFIO mlx5 driver in rdma-core. It uses an RDMA loopback QP
> to issue RDMA WRITE operations which effectively perform memory
> copies using DMA. Since mlx5 has a stable programming ABI this
> should work on devices from CX5 to current HW. The device FW must
> support the QP loopback configuration.
> 
> Also support send_msi by arming completion events of the RDMA WRITE
> to trigger MSI delivery.
> 
> mlx5 device startup is very complex and most of this code is just
> booting the device, with a smaller amount for operating the QP.
> 
> This entire series was coded by Claude Code in about 4 days. It
> used about 4.5M output tokens, 30 individual sessions and 5600 lines
> of AI-generated .md files. I spent an annoying amount of time
> de-slopping and cleaning its work product to make it presentable.
> However, previous VFIO drivers have taken on the order of 1-2
> months to write, so getting one in a week is pretty remarkable.
> 
> For those interested, the flow I used was broadly a prompt sequence
> sort of like:
> 
>  - Hey Claude, go look at the falcon series, VFIO self test, the
>    mlx5 driver, rdma-core and some PDF documentation and make a
>    plan to put mlx5 under the selftest.
>  - Write an rdma-core application using the built-in VFIO provider
>    that can do the required memcpy operations that vfio selftests
>    wants.
>    (This resulted in a 1k loc C file that compiled and ran the
>     first time but had a few bugs related to device programming
>     that the AI resolved.)
>  - Replace the rdma-core components with open-coded versions to
>    create a fully stand-alone program that does the DMA memcpy.
>  - Review and audit the thing.
>  [Pause and de-slop it]
>  - Make it work on a PF too (this is surprisingly hard!).
>  [Move to a kernel tree and copy all the .md files and .c program
>   it made]
>  - Hey Claude, look at all this stuff and make a broad plan to
>    actually build a VFIO self test.
>  - Here is my 1 sentence advice on what each patch should look
>    like, make a detailed plan to make a patch for every one.
>  [Pause and polish the patch plans]
>  - Execute plan X then commit it [pause and de-slop each patch,
>    repeat].
>  [Review and final polish]
> eeb2cc76b0b4
> v7:
>  - Fix some compilation problems, kvm and the igb

Applied to vfio next branch for v7.4.  Topic branch published as
mlx5-vfio-selftest-v7[1] for conflict management.  Thanks,

Alex

[1]https://github.com/awilliam/linux-vfio.git mlx5-vfio-selftest-v7