linux-kernel - Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP

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Date:   Wed, 28 Jun 2017 05:17:13 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer
 XDP

On Wed, Jun 28, 2017 at 10:14:34AM +0800, Jason Wang wrote:
> 
> 
> On 2017年06月28日 10:02, Michael S. Tsirkin wrote:
> > On Wed, Jun 28, 2017 at 09:54:03AM +0800, Jason Wang wrote:
> > > We should allow csumed packet for small buffer, otherwise XDP_PASS
> > > won't work correctly.
> > > 
> > > Fixes commit bb91accf2733 ("virtio-net: XDP support for small buffers")
> > > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > The issue would be VIRTIO_NET_HDR_F_DATA_VALID might be set.
> > What do you think?
> 
> I think it's safe. For XDP_PASS, it work like in the past.

That's the part I don't get. With DATA_VALID csum in packet is wrong, XDP
tools assume it's value.

> For XDP_TX, we
> zero the vnet header.

Again TX offload is disabled, so packets will go out with an invalid
checksum.

> For adjusting header, XDP prog should deal with csum.
> 
> Thanks

That part seems right.

> > 
> > > ---
> > > The patch is needed for -stable.
> > > ---
> > >   drivers/net/virtio_net.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 143d8a9..499fcc9 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -413,7 +413,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > >   		void *orig_data;
> > >   		u32 act;
> > > -		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
> > > +		if (unlikely(hdr->hdr.gso_type))
> > >   			goto err_xdp;
> > >   		xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len;
> > > -- 
> > > 2.7.4