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

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Message-ID: <20251231094052-mutt-send-email-mst@kernel.org>
Date: Wed, 31 Dec 2025 09:42:41 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Petr Tesarik <ptesarik@...e.com>
Cc: linux-kernel@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Olivia Mackall <olivia@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Jason Wang <jasowang@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Stefano Garzarella <sgarzare@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Leon Romanovsky <leon@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>, linux-doc@...r.kernel.org,
	linux-crypto@...r.kernel.org, virtualization@...ts.linux.dev,
	linux-scsi@...r.kernel.org, iommu@...ts.linux.dev,
	kvm@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC 00/13] fix DMA aligment issues around virtio

On Wed, Dec 31, 2025 at 02:12:24PM +0100, Petr Tesarik wrote:
> On Tue, 30 Dec 2025 05:15:42 -0500
> "Michael S. Tsirkin" <mst@...hat.com> 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/
> > 
> > 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.

Oh right sorry I forgot to mention it.  It's this one:

https://lore.kernel.org/all/20251230064649.55597-8-jasowang@redhat.com/

one can just do

b4 shazam 20251230064649.55597-8-jasowang@...hat.com


> 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(-)
> >