On Tue, 30 Dec 2025 05:15:42 -0500
"Michael S. Tsirkin" [off-list ref] 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@gmail.com/ (local)

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(-)