On Tue, Apr 19, 2022 at 04:12:31PM +0200, Maciej Szymański wrote:
> Hello,
>
> I've found a problem in virtio-net driver.
> If virtio-net backend device advertises guest offload features, there is
> an unpermitted usage of control virtqueue before driver is initialized.
> According to VIRTIO specification 2.1.2 :
> "The device MUST NOT consume buffers or send any used buffer
> notifications to the driver before DRIVER_OK."
Right.
> During an initialization, driver calls register_netdevice which invokes
> callback function virtnet_set_features from __netdev_update_features.
> If guest offload features are advertised by the device,
> virtnet_set_guest_offloads is using virtnet_send_command to write and
> read from VQ.
> That leads to initialization stuck as device is not permitted yet to use VQ.
Hmm so we have this:
if ((dev->features ^ features) & NETIF_F_GRO_HW) {
if (vi->xdp_enabled)
return -EBUSY;
if (features & NETIF_F_GRO_HW)
offloads = vi->guest_offloads_capable;
else
offloads = vi->guest_offloads_capable &
~GUEST_OFFLOAD_GRO_HW_MASK;
err = virtnet_set_guest_offloads(vi, offloads);
if (err)
return err;
vi->guest_offloads = offloads;
}
which I guess should have prevented virtnet_set_guest_offloads from ever running.
