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

[Jason Wang]

On 2017å06æ28æ 10:17, Michael S. Tsirkin wrote:
> On Wed, Jun 28, 2017 at 10:14:34AM +0800, Jason Wang wrote:
> > On 2017å06æ28æ 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@xxxxxxxxxx>
> > > 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.

DATA_VALID is CHECKSUM_UNCESSARY on the host, and according to the 
comment in skbuff.h


"
 *   The hardware you're dealing with doesn't calculate the full checksum
 *   (as in CHECKSUM_COMPLETE), but it does parse headers and verify 
checksums
 *   for specific protocols. For such packets it will set 
CHECKSUM_UNNECESSARY
 *   if their checksums are okay. skb->csum is still undefined in this case
 *   though. A driver or device must never modify the checksum field in the
 *   packet even if checksum is verified.
"

The csum is correct I believe?

Thanks

> > 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