From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, Jesper Dangaard Brouer <brouer@redhat.com>
Subject: Re: [PATCH net-next 1/2] virtio-net: don't reserve space for vnet header for XDP
Date: Wed, 6 May 2020 05:54:46 -0400 [thread overview]
Message-ID: <20200506055436-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <7a169b06-b6b9-eac1-f03a-39dd1cfcce57@redhat.com>
On Wed, May 06, 2020 at 04:19:40PM +0800, Jason Wang wrote:
>
> On 2020/5/6 下午3:53, Michael S. Tsirkin wrote:
> > On Wed, May 06, 2020 at 02:16:32PM +0800, Jason Wang wrote:
> > > We tried to reserve space for vnet header before
> > > xdp.data_hard_start. But this is useless since the packet could be
> > > modified by XDP which may invalidate the information stored in the
> > > header and there's no way for XDP to know the existence of the vnet
> > > header currently.
> > What do you mean? Doesn't XDP_PASS use the header in the buffer?
>
>
> We don't, see 436c9453a1ac0 ("virtio-net: keep vnet header zeroed after
> processing XDP")
>
> If there's other place, it should be a bug.
>
>
> >
> > > So let's just not reserve space for vnet header in this case.
> > In any case, we can find out XDP does head adjustments
> > if we need to.
>
>
> But XDP program can modify the packets without adjusting headers.
>
> Thanks
Then what's the problem?
>
> >
> >
> > > Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > ---
> > > drivers/net/virtio_net.c | 6 +++---
> > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 11f722460513..98dd75b665a5 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -684,8 +684,8 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > > page = xdp_page;
> > > }
> > > - xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len;
> > > - xdp.data = xdp.data_hard_start + xdp_headroom;
> > > + xdp.data_hard_start = buf + VIRTNET_RX_PAD;
> > > + xdp.data = xdp.data_hard_start + xdp_headroom + vi->hdr_len;
> > > xdp.data_end = xdp.data + len;
> > > xdp.data_meta = xdp.data;
> > > xdp.rxq = &rq->xdp_rxq;
> > > @@ -845,7 +845,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > > * the descriptor on if we get an XDP_TX return code.
> > > */
> > > data = page_address(xdp_page) + offset;
> > > - xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len;
> > > + xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM;
> > > xdp.data = data + vi->hdr_len;
> > > xdp.data_end = xdp.data + (len - vi->hdr_len);
> > > xdp.data_meta = xdp.data;
> > > --
> > > 2.20.1
next prev parent reply other threads:[~2020-05-06 9:54 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 6:16 [PATCH net-next 1/2] virtio-net: don't reserve space for vnet header for XDP Jason Wang
2020-05-06 6:16 ` [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers Jason Wang
2020-05-06 7:37 ` Michael S. Tsirkin
2020-05-06 8:21 ` Jason Wang
2020-05-06 12:08 ` Michael S. Tsirkin
2020-05-08 1:54 ` Jason Wang
2020-05-06 7:53 ` [PATCH net-next 1/2] virtio-net: don't reserve space for vnet header for XDP Michael S. Tsirkin
2020-05-06 8:19 ` Jason Wang
2020-05-06 9:54 ` Michael S. Tsirkin [this message]
2020-05-08 1:56 ` Jason Wang
2020-05-06 8:21 ` Jesper Dangaard Brouer
2020-05-06 8:34 ` Jason Wang
2020-05-06 9:46 ` Michael S. Tsirkin
2020-05-08 1:59 ` Jason Wang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200506055436-mutt-send-email-mst@kernel.org \
--to=mst@redhat.com \
--cc=bpf@vger.kernel.org \
--cc=brouer@redhat.com \
--cc=jasowang@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).