On Mon, Jan 15, 2024 at 05:32:25PM -0500, Michael S. Tsirkin wrote: > On Mon, Jan 15, 2024 at 09:48:40PM +0200, Andrew Melnychenko wrote: > > When the Qemu launched with vhost but without tap vnet_hdr, > > vhost tries to copy vnet_hdr from socket iter with size 0 > > to the page that may contain some trash. > > That trash can be interpreted as unpredictable values for > > vnet_hdr. > > That leads to dropping some packets and in some cases to > > stalling vhost routine when the vhost_net tries to process > > packets and fails in a loop. > > > > Qemu options: > > -netdev tap,vhost=on,vnet_hdr=off,... > > > > Signed-off-by: Andrew Melnychenko <andrew@xxxxxxxxxx> > > --- > > drivers/vhost/net.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index f2ed7167c848..57411ac2d08b 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -735,6 +735,9 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq, > > hdr = buf; > > gso = &hdr->gso; > > > > + if (!sock_hlen) > > + memset(buf, 0, pad); > > + > > if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && > > vhost16_to_cpu(vq, gso->csum_start) + > > vhost16_to_cpu(vq, gso->csum_offset) + 2 > > > > Hmm need to analyse it to make sure there are no cases where we leak > some data to guest here in case where sock_hlen is set ... Could you post this analysis pls? > > -- > > 2.43.0
