Re: [PATCH net 4/9] virtio-net: correctly handle XDP_PASS for linearized packets

[Jason Wang]

On 2016å12æ23æ 23:57, John Fastabend wrote:
> On 16-12-23 06:37 AM, Jason Wang wrote:
> > When XDP_PASS were determined for linearized packets, we try to get
> > new buffers in the virtqueue and build skbs from them. This is wrong,
> > we should create skbs based on existed buffers instead. Fixing them by
> > creating skb based on xdp_page.
> >
> > With this patch "ping 192.168.100.4 -s 3900 -M do" works for XDP_PASS.
> >
> > Cc: John Fastabend <john.r.fastabend@xxxxxxxxx>
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   drivers/net/virtio_net.c | 10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 58ad40e..470293e 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -578,8 +578,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> >   		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
> >   		switch (act) {
> >   		case XDP_PASS:
> > -			if (unlikely(xdp_page != page))
> > -				__free_pages(xdp_page, 0);
> > +			/* We can only create skb based on xdp_page. */
> > +			if (unlikely(xdp_page != page)) {
> > +				rcu_read_unlock();
> > +				put_page(page);
> > +				head_skb = page_to_skb(vi, rq, xdp_page,
> > +						       0, len, PAGE_SIZE);
> > +				return head_skb;
> > +			}
> >   			break;
> >   		case XDP_TX:
> >   			if (unlikely(xdp_page != page))
> Great thanks. This was likely working before because of the memory
> leak fixed in 3/9.

Looks not, without this and 3/9 the code will try to get buffers and 
build skb for a new packet instead of existed buffers.

Thanks

> Acked-by: John Fastabend <john.r.fastabend@xxxxxxxxx>