Re: [PATCH v8 0/5] Support message-based DMA in vfio-user server

[Mattias Nissler]

Stefan, to the best of my knowledge this is fully reviewed and ready
to go in - can you kindly pick it up or advise in case there's
something I missed? Thanks!

On Mon, Mar 4, 2024 at 11:25 AM Peter Xu <peterx@redhat.com> wrote:
>
> On Mon, Mar 04, 2024 at 02:05:49AM -0800, Mattias Nissler wrote:
> > This series adds basic support for message-based DMA in qemu's vfio-user
> > server. This is useful for cases where the client does not provide file
> > descriptors for accessing system memory via memory mappings. My motivating 
> > use
> > case is to hook up device models as PCIe endpoints to a hardware design. 
> > This
> > works by bridging the PCIe transaction layer to vfio-user, and the endpoint
> > does not access memory directly, but sends memory requests TLPs to the 
> > hardware
> > design in order to perform DMA.
> >
> > Note that more work is needed to make message-based DMA work well: qemu
> > currently breaks down DMA accesses into chunks of size 8 bytes at maximum, 
> > each
> > of which will be handled in a separate vfio-user DMA request message. This 
> > is
> > quite terrible for large DMA accesses, such as when nvme reads and writes
> > page-sized blocks for example. Thus, I would like to improve qemu to be 
> > able to
> > perform larger accesses, at least for indirect memory regions. I have 
> > something
> > working locally, but since this will likely result in more involved surgery 
> > and
> > discussion, I am leaving this to be addressed in a separate patch.
>
> No objection from my side memory-wise.  It'll be good to get some words
> from Paolo if possible.
>
> Copy Peter Maydell due to the other relevant discussion.
>
> https://lore.kernel.org/qemu-devel/20240228125939.56925-1-heinrich.schuchardt@canonical.com/
>
> --
> Peter Xu
>