Re: [PATCH RFC 00/13] fix DMA aligment issues around virtio

[Petr Tesarik]

On Tue, 30 Dec 2025 05:15:42 -0500
"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:

> Cong Wang reported dma debug warnings with virtio-vsock
> and proposed a patch, see:
> 
> https://lore.kernel.org/all/20251228015451.1253271-1-xiyou.wangcong@xxxxxxxxx/
> 
> however, the issue is more widespread.
> This is an attempt to fix it systematically.
> Note: i2c and gio might also be affected, I am still looking
> into it. Help from maintainers welcome.
> 
> Early RFC, compile tested only. Sending for early feedback/flames.
> Cursor/claude used liberally mostly for refactoring, and english.
> 
> DMA maintainers, could you please confirm the DMA core changes
> are ok with you?

Before anyone else runs into the same issue as I did: This patch series
does not apply cleanly unless you first apply commit b148e85c918a
("virtio_ring: switch to use vring_virtqueue for virtqueue_add
variants") from the mst/vhost/vhost branch.

But if you go to the trouble of adding the mst/vhost remote, then the
above-mentioned branch also contains this patch series, and it's
probably the best place to find the patched code...

Now, let me set out for review.

Petr T

> Thanks!
> 
> 
> Michael S. Tsirkin (13):
>   dma-mapping: add __dma_from_device_align_begin/end
>   docs: dma-api: document __dma_align_begin/end
>   dma-mapping: add DMA_ATTR_CPU_CACHE_CLEAN
>   docs: dma-api: document DMA_ATTR_CPU_CACHE_CLEAN
>   dma-debug: track cache clean flag in entries
>   virtio: add virtqueue_add_inbuf_cache_clean API
>   vsock/virtio: fix DMA alignment for event_list
>   vsock/virtio: use virtqueue_add_inbuf_cache_clean for events
>   virtio_input: fix DMA alignment for evts
>   virtio_scsi: fix DMA cacheline issues for events
>   virtio-rng: fix DMA alignment for data buffer
>   virtio_input: use virtqueue_add_inbuf_cache_clean for events
>   vsock/virtio: reorder fields to reduce struct padding
> 
>  Documentation/core-api/dma-api-howto.rst  | 42 +++++++++++++
>  Documentation/core-api/dma-attributes.rst |  9 +++
>  drivers/char/hw_random/virtio-rng.c       |  2 +
>  drivers/scsi/virtio_scsi.c                | 18 ++++--
>  drivers/virtio/virtio_input.c             |  5 +-
>  drivers/virtio/virtio_ring.c              | 72 +++++++++++++++++------
>  include/linux/dma-mapping.h               | 17 ++++++
>  include/linux/virtio.h                    |  5 ++
>  kernel/dma/debug.c                        | 26 ++++++--
>  net/vmw_vsock/virtio_transport.c          |  8 ++-
>  10 files changed, 172 insertions(+), 32 deletions(-)
>