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 03:53:31 -0400 Message-ID: <20200506033834-mutt-send-email-mst@kernel.org> References: <20200506061633.16327-1-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200506061633.16327-1-jasowang@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 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? > 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. > 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