On Tue, Apr 19, 2022 at 11:03 PM Michael S. Tsirkin <[email protected]> wrote:
>
> 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.
>
> From your description it sounds like you have observed this
> in practice, right?
>
>
>
> > I have attached a patch for kernel 5.18-rc3 which fixes the problem by
> > deferring feature set after virtio driver initialization.
> >
> > Best Regards,
> >
> > --
> > Maciej Szymański
> > Senior Staff Engineer
> >
> > OpenSynergy GmbH
> > Rotherstr. 20, 10245 Berlin
> >
> > Phone: +49 30 60 98 54 0 -86
> > Fax: +49 30 60 98 54 0 -99
> > E-Mail: [email protected]
> >
> > www.opensynergy.com
> >
> > Handelsregister/Commercial Registry: Amtsgericht Charlottenburg, HRB 108616B
> > Geschäftsführer/Managing Director: Regis Adjamah
> >
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>
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 87838cb..a44462d 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -264,6 +264,8 @@ struct virtnet_info {
> > unsigned long guest_offloads;
> > unsigned long guest_offloads_capable;
> >
> > + netdev_features_t features;
> > +
>
> I don't much like how we are forced to keep a copy of features
> here :( At least pls add a comment explaining what's going on,
> who owns this etc.
>
> > /* failover when STANDBY feature enabled */
> > struct failover *failover;
> > };
> > @@ -2976,6 +2978,15 @@ static int virtnet_get_phys_port_name(struct
> > net_device *dev, char *buf,
> >
> > static int virtnet_set_features(struct net_device *dev,
> > netdev_features_t features)
> > +{
> > + struct virtnet_info *vi = netdev_priv(dev);
> > + vi->features = features;
> > +
> > + return 0;
> > +}
>
>
> Looks like this breaks changing features after initialization -
> these will never be propagated to hardware now.
Yes, I think we need to have a check and only defer the setting when
virtio device is not ready.
Thanks
>
> > +
> > +static int virtnet_set_features_deferred(struct net_device *dev,
> > + netdev_features_t features)
> > {
> > struct virtnet_info *vi = netdev_priv(dev);
> > u64 offloads;
> > @@ -3644,6 +3655,13 @@ static int virtnet_probe(struct virtio_device *vdev)
> >
> > virtio_device_ready(vdev);
> >
> > + /* Deferred feature set after device ready */
> > + err = virtnet_set_features_deferred(dev, vi->features);
>
>
> It seems that if this is called e.g. for a device without a CVQ and
> there are things that actually need to change then it will BUG_ON.
>
>
> > + if (err) {
> > + pr_debug("virtio_net: set features failed\n");
> > + goto free_unregister_netdev;
> > + }
> > +
> > err = virtnet_cpu_notif_add(vi);
> > if (err) {
> > pr_debug("virtio_net: registering cpu notifier failed\n");
> >
>
> --
> MST
>
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