netdev - Re: [PATCH vhost v13 04/12] virtio_ring: support add premapped buf

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Date: Tue, 4 Jun 2024 18:17:44 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Ilya Leoshkevich <iii@...ux.ibm.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, virtualization@...ts.linux-foundation.org, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, 
	John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org, bpf@...r.kernel.org, 
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH vhost v13 04/12] virtio_ring: support add premapped buf

On Tue, Jun 4, 2024 at 6:07 PM Ilya Leoshkevich <iii@...ux.ibm.com> wrote:
>
> On Thu, 2023-08-10 at 20:30 +0800, Xuan Zhuo wrote:
> > If the vq is the premapped mode, use the sg_dma_address() directly.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >  drivers/virtio/virtio_ring.c | 19 +++++++++++++++++--
> >  1 file changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c
> > b/drivers/virtio/virtio_ring.c
> > index 8e81b01e0735..f9f772e85a38 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -361,6 +361,11 @@ static struct device *vring_dma_dev(const struct
> > vring_virtqueue *vq)
> >  static int vring_map_one_sg(const struct vring_virtqueue *vq, struct
> > scatterlist *sg,
> >                           enum dma_data_direction direction,
> > dma_addr_t *addr)
> >  {
> > +     if (vq->premapped) {
> > +             *addr = sg_dma_address(sg);
> > +             return 0;
> > +     }
> > +
>
> I wonder if something needs to be done for KMSAN here, like it's done
> by the next block in this function? I'm looking into what seems to be a
> KMSAN false positive on s390x:
>
> BUG: KMSAN: uninit-value in receive_buf+0x45ca/0x6990
>  receive_buf+0x45ca/0x6990
>  virtnet_poll+0x17e0/0x3130
>  net_rx_action+0x832/0x26e0
>  handle_softirqs+0x330/0x10f0
>  [...]

I think there's a similar problem on x86 as well:
https://syzkaller.appspot.com/bug?extid=c5336dcd1b741349d27a

I was going to look closer this week.