Messages in this thread | | | Subject | Re: [PATCH net-next 1/2] virtio-net: don't reserve space for vnet header for XDP | From | Jason Wang <> | Date | Wed, 6 May 2020 16:19:40 +0800 |
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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
> > >> 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
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