Re: [GIT PULL] Please pull mlx5 VFIO PCI DMA conversion

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 13 May 2025 13:48:10 +0300
Leon Romanovsky <leon@kernel.org> wrote:

> Hi Alex,
> 
> Please accept this pull request, which presents subset of new DMA-API
> patchset [1] specific for VFIO subsystem.
> 
> It is based on Marek's dma-mapping-for-6.16-two-step-api branch, so merging
> now will allow us to reduce possible rebase errors in mlx5 vfio code and give
> enough time to start to work on second driver conversion. Such conversion will
> allow us to generalize the API for VFIO kernel drivers, in similiar way that
> was done for RDMA, HMM and block layers.

Hi Leon,

Pull requests are not my typical workflow.  Are these mlx5-vfio-pci
changes intended to enter mainline through the vfio tree or your rdma
tree?  Why do the commits not include a review/ack from Yishai?

Typically I'd expect a patch series for the mlx5-vfio-pci changes that
I would apply, with Yishai's approval, to a shared branch containing the
commits Marek has already accepted.  I'm not sure why we're preempting
that process here.  Thanks,

Alex

> [1] [PATCH v10 00/24] Provide a new two step DMA mapping API
> https://lore.kernel.org/all/cover.1745831017.git.leon@kernel.org/
> 
> ----------------------------------------------------------------
> The following changes since commit 3ee7d9496342246f4353716f6bbf64c945ff6e2d:
> 
>   docs: core-api: document the IOVA-based API (2025-05-06 08:36:54 +0200)
> 
> are available in the Git repository at:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git tags/vfio-dma-two-step
> 
> for you to fetch changes up to 855c89a25e1756b7699b863afd4d6afcbd0de0d6:
> 
>   vfio/mlx5: Enable the DMA link API (2025-05-13 03:58:27 -0400)
> 
> ----------------------------------------------------------------
> Convert mlx5 VFIO PCI driver to new two step DMA API
> 
> This PR is based on newly accepted DMA API, which allows us
> to avoid building scatter-gather lists just to batch mapping
> and unmapping of pages.
> 
> VFIO PCI live migration code is building a very large "page list"
> for the device. Instead of allocating a scatter list entry per
> allocated page it can just allocate an array of 'struct page *',
> saving a large amount of memory.
> 
> Signed-off-by: Leon Romanovsky <leon@kernel.org>
> 
> ----------------------------------------------------------------
> Leon Romanovsky (3):
>       vfio/mlx5: Explicitly use number of pages instead of allocated length
>       vfio/mlx5: Rewrite create mkey flow to allow better code reuse
>       vfio/mlx5: Enable the DMA link API
> 
>  drivers/vfio/pci/mlx5/cmd.c  | 375 +++++++++++++++++++++----------------------
>  drivers/vfio/pci/mlx5/cmd.h  |  35 ++--
>  drivers/vfio/pci/mlx5/main.c |  87 +++++-----
>  3 files changed, 239 insertions(+), 258 deletions(-)
>