On Thu, Nov 25, 2021 at 03:26:22PM +0800, Jason Wang wrote: > On Thu, Nov 25, 2021 at 3:20 PM Eli Cohen <elic@xxxxxxxxxx> wrote: > > > > On Thu, Nov 25, 2021 at 03:15:33PM +0800, Jason Wang wrote: > > > On Thu, Nov 25, 2021 at 3:09 PM Eli Cohen <elic@xxxxxxxxxx> wrote: > > > > > > > > On Thu, Nov 25, 2021 at 02:05:47PM +0800, Jason Wang wrote: > > > > > When VIRTIO_NET_F_MTU feature is not negotiated, we assume a very > > > > > large max_mtu. In this case, using small packet mode is not correct > > > > > since it may breaks the networking when MTU is grater than > > > > > ETH_DATA_LEN. > > > > > > > > > > To have a quick fix, simply enable the big packet mode when > > > > > VIRTIO_NET_F_MTU is not negotiated. We can do optimization on top. > > > > > > > > > > Reported-by: Eli Cohen <elic@xxxxxxxxxx> > > > > > Cc: Eli Cohen <elic@xxxxxxxxxx> > > > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > > > > --- > > > > > drivers/net/virtio_net.c | 7 ++++--- > > > > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > index 7c43bfc1ce44..83ae3ef5eb11 100644 > > > > > --- a/drivers/net/virtio_net.c > > > > > +++ b/drivers/net/virtio_net.c > > > > > @@ -3200,11 +3200,12 @@ static int virtnet_probe(struct virtio_device *vdev) > > > > > dev->mtu = mtu; > > > > > dev->max_mtu = mtu; > > > > > > > > > > - /* TODO: size buffers correctly in this case. */ > > > > > - if (dev->mtu > ETH_DATA_LEN) > > > > > - vi->big_packets = true; > > > > > } > > > > > > > > > > + /* TODO: size buffers correctly in this case. */ > > > > > + if (dev->max_mtu > ETH_DATA_LEN) > > > > > + vi->big_packets = true; > > > > > + > > > > > > > > If VIRTIO_NET_F_MTU is provided, then dev->max_mtu is going to equal > > > > ETH_DATA_LEN (will be set in ether_setup()) so I don't think it will set > > > > big_packets to true. > > > > > > I may miss something, the dev->max_mtu is just assigned to the mtu > > > value read from the config space in the code block above (inside the > > > feature check of VIRTIO_NET_F_MTU). > > > > Sorry, I meant "If VIRTIO_NET_F_MTU is ***NOT*** provided". In that case > > dev->max_mtu eauals ETH_DATA_LEN so you won't set vi->big_packets to > > true. > > I see but in this case, the above assignment: > > /* MTU range: 68 - 65535 */ > dev->min_mtu = MIN_MTU; > dev->max_mtu = MAX_MTU; > > happens after alloc_etherdev_mq() which calls ether_setup(), so we are > probably fine here. > > Thanks Actually the issue with VIRTIO_NET_F_MTU is that devices might be tempted to expose 9k here simply because they support jumbo frames, if they also don't support mergeable buffers this will force big packet mode. > > > > > > > > Thanks > > > > > > > > > > > > > > > > if (vi->any_header_sg) > > > > > dev->needed_headroom = vi->hdr_len; > > > > > > > > > > -- > > > > > 2.25.1 > > > > > > > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
