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Tsirkin" Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Jesper Dangaard Brouer References: <20200506061633.16327-1-jasowang@redhat.com> <20200506033834-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <7a169b06-b6b9-eac1-f03a-39dd1cfcce57@redhat.com> Date: Wed, 6 May 2020 16:19:40 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200506033834-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/5/6 =E4=B8=8B=E5=8D=883:53, 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=20 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 > > >> 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_de= vice *dev, >> page =3D xdp_page; >> } >> =20 >> - xdp.data_hard_start =3D buf + VIRTNET_RX_PAD + vi->hdr_len; >> - xdp.data =3D xdp.data_hard_start + xdp_headroom; >> + xdp.data_hard_start =3D buf + VIRTNET_RX_PAD; >> + xdp.data =3D xdp.data_hard_start + xdp_headroom + vi->hdr_len; >> xdp.data_end =3D xdp.data + len; >> xdp.data_meta =3D xdp.data; >> xdp.rxq =3D &rq->xdp_rxq; >> @@ -845,7 +845,7 @@ static struct sk_buff *receive_mergeable(struct ne= t_device *dev, >> * the descriptor on if we get an XDP_TX return code. >> */ >> data =3D page_address(xdp_page) + offset; >> - xdp.data_hard_start =3D data - VIRTIO_XDP_HEADROOM + vi->hdr_len; >> + xdp.data_hard_start =3D data - VIRTIO_XDP_HEADROOM; >> xdp.data =3D data + vi->hdr_len; >> xdp.data_end =3D xdp.data + (len - vi->hdr_len); >> xdp.data_meta =3D xdp.data; >> --=20 >> 2.20.1