netdev - Re: [PATCH v2 07/15] vsock/virtio: fix DMA alignment for event

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Message-ID: <20260108090639-mutt-send-email-mst@kernel.org>
Date: Thu, 8 Jan 2026 09:07:53 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.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>,
	"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>, Petr Tesarik <ptesarik@...e.com>,
	Leon Romanovsky <leon@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>,
	Bartosz Golaszewski <brgl@...nel.org>, 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 v2 07/15] vsock/virtio: fix DMA alignment for event_list

On Thu, Jan 08, 2026 at 03:04:07PM +0100, Stefano Garzarella wrote:
> On Mon, Jan 05, 2026 at 03:23:17AM -0500, Michael S. Tsirkin wrote:
> > On non-cache-coherent platforms, when a structure contains a buffer
> > used for DMA alongside fields that the CPU writes to, cacheline sharing
> > can cause data corruption.
> > 
> > The event_list array is used for DMA_FROM_DEVICE operations via
> > virtqueue_add_inbuf(). The adjacent event_run and guest_cid fields are
> > written by the CPU while the buffer is available, so mapped for the
> > device. If these share cachelines with event_list, CPU writes can
> > corrupt DMA data.
> > 
> > Add __dma_from_device_group_begin()/end() annotations to ensure event_list
> > is isolated in its own cachelines.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> > net/vmw_vsock/virtio_transport.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > index 8c867023a2e5..bb94baadfd8b 100644
> > --- a/net/vmw_vsock/virtio_transport.c
> > +++ b/net/vmw_vsock/virtio_transport.c
> > @@ -17,6 +17,7 @@
> > #include <linux/virtio_ids.h>
> > #include <linux/virtio_config.h>
> > #include <linux/virtio_vsock.h>
> > +#include <linux/dma-mapping.h>
> > #include <net/sock.h>
> > #include <linux/mutex.h>
> > #include <net/af_vsock.h>
> > @@ -59,8 +60,9 @@ struct virtio_vsock {
> > 	 */
> > 	struct mutex event_lock;
> > 	bool event_run;
> > +	__dma_from_device_group_begin();
> > 	struct virtio_vsock_event event_list[8];
> > -
> > +	__dma_from_device_group_end();
> 
> Can we keep the blank line before `guest_cid` so that the comment before
> this section makes sense? (regarding the lock required to access these
> fields)
> 
> Thanks,
> Stefano

A follow up patch re-introduces it, so I don't think it matters?

> > 	u32 guest_cid;
> > 	bool seqpacket_allow;
> > 
> > -- 
> > MST
> >