linux-kernel - Re: [PATCH v2 2/3] virtio_net: Add missing virtio header in skb for XDP

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Message-ID: <CAKhg4tJRM4qMJBwNs=HWczq7muw0_m_szH8L0CDaxpC+kJSeNw@mail.gmail.com>
Date: Thu, 25 Jan 2024 14:52:48 +0800
From: Liang Chen <liangchen.linux@...il.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v2 2/3] virtio_net: Add missing virtio header in skb for XDP_PASS

On Wed, Jan 24, 2024 at 7:04 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
>
>
> 在 2024/1/24 下午4:57, Liang Chen 写道:
> > For the XDP_PASS scenario of the XDP path, the skb constructed with
> > xdp_buff does not include the virtio header. Adding the virtio header
> > information back when creating the skb.
> >
> > Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> > ---
> >   drivers/net/virtio_net.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index b56828804e5f..2de46eb4c661 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1270,6 +1270,9 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> >       if (unlikely(!skb))
> >               goto err;
> >
> > +     /* Store the original virtio header for subsequent use by the driver. */
> > +     memcpy(skb_vnet_common_hdr(skb), &virtnet_xdp.hdr, vi->hdr_len);
>
> If xdp push or xdp pull modifies xdp_buff, will the original header
> still apply to the modified data?
>

No, it would be an issue then. Anyway, this patch will be dropped in v3. Thanks.

> Thanks,
> Heng
>
> > +
> >       if (metasize)
> >               skb_metadata_set(skb, metasize);
> >
> > @@ -1635,6 +1638,9 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> >               head_skb = build_skb_from_xdp_buff(dev, vi, xdp, xdp_frags_truesz);
> >               if (unlikely(!head_skb))
> >                       break;
> > +             /* Store the original virtio header for subsequent use by the driver. */
> > +             memcpy(skb_vnet_common_hdr(head_skb), &virtnet_xdp.hdr, vi->hdr_len);
> > +
> >               return head_skb;
> >
> >       case XDP_TX:
>