Re: [PATCH net 1/2] virtio-net: disable guest csum during XDP set

[Jason Wang]

On 2018/11/24 äå4:01, David Miller wrote:
> From: Jason Wang <jasowang@xxxxxxxxxx>
> Date: Thu, 22 Nov 2018 14:36:30 +0800
>
> > We don't disable VIRTIO_NET_F_GUEST_CSUM if XDP was set. This means we
> > can receive partial csumed packets with metadata kept in the
> > vnet_hdr. This may have several side effects:
> >
> > - It could be overridden by header adjustment, thus is might be not
> >    correct after XDP processing.
> > - There's no way to pass such metadata information through
> >    XDP_REDIRECT to another driver.
> > - XDP does not support checksum offload right now.
> >
> > So simply disable guest csum if possible in this the case of XDP.
> >
> > Fixes: 3f93522ffab2d ("virtio-net: switch off offloads on demand if possible on XDP set")
> > Reported-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> > Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> > Cc: Pavel Popa <pashinho1990@xxxxxxxxx>
> > Cc: David Ahern <dsahern@xxxxxxxxx>
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> Applied and queued up for -stable.
>
> We really should have a way to use the checksum provided if the XDP
> program returns XDP_PASS and does not modify the packet contents
> or size.


Yes, I think this may require the assistance of BPF verifier to set a 
flag or other. Then we can assume the metadata is safe to use.

Thanks