From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" 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 Message-ID: <20200506055436-mutt-send-email-mst@kernel.org> References: <20200506061633.16327-1-jasowang@redhat.com> <20200506033834-mutt-send-email-mst@kernel.org> <7a169b06-b6b9-eac1-f03a-39dd1cfcce57@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <7a169b06-b6b9-eac1-f03a-39dd1cfcce57@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Jason Wang Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Jesper Dangaard Brouer List-Id: virtualization@lists.linuxfoundation.org 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 > > > Signed-off-by: Jason Wang > > > --- > > > 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