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

[Leon Romanovsky <leon@kernel.org>]

On Thu, May 15, 2025 at 11:47:15AM -0600, Alex Williamson wrote:
> 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?

VFIO changes will come through your tree. DMA patches are the same as in
Marek's DMA tree and in our RDMA tree.

I prepared PR to save from your hassle of merging dma/dma-mapping-for-6.16-two-step-api
topic from Marek and collecting VFIO patches from ML.

> Why do the commits not include a review/ack from Yishai?

They have Jason's review tags and as far as I know Yishai, he trusts
Jason's judgement.

> 
> 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,

This is exactly what is in this PR: reviewed VFIO patches which were
posted to the ML on top of Marek's shared branch.

If you prefer, I can repost the VFIO patches.

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(-)
> > 
>