Subject: Re: [PATCH net-next v3 3/3] virtio-net: synchronize operstate with admin state on up/down

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 17 Jul 2024 02:00:23 -0400

On Wed, Jul 17, 2024 at 09:19:02AM +0800, Jason Wang wrote:
> On Wed, Jul 10, 2024 at 11:03 AM Jason Wang <[email-masked]> wrote:
> >
> > On Tue, Jul 9, 2024 at 9:28 PM Michael S. Tsirkin <[email-masked]> wrote:
> > >
> > > On Tue, Jul 09, 2024 at 04:02:14PM +0800, Jason Wang wrote:
> > > > This patch synchronize operstate with admin state per RFC2863.
> > > >
> > > > This is done by trying to toggle the carrier upon open/close and
> > > > synchronize with the config change work. This allows propagate status
> > > > correctly to stacked devices like:
> > > >
> > > > ip link add link enp0s3 macvlan0 type macvlan
> > > > ip link set link enp0s3 down
> > > > ip link show
> > > >
> > > > Before this patch:
> > > >
> > > > 3: enp0s3: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
> > > >     link/ether 00:00:05:00:00:09 brd ff:ff:ff:ff:ff:ff
> > > > ......
> > > > 5: macvlan0@enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
> > > >     link/ether b2:a9:c5:04:da:53 brd ff:ff:ff:ff:ff:ff
> > > >
> > > > After this patch:
> > > >
> > > > 3: enp0s3: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
> > > >     link/ether 00:00:05:00:00:09 brd ff:ff:ff:ff:ff:ff
> > > > ...
> > > > 5: macvlan0@enp0s3: <NO-CARRIER,BROADCAST,MULTICAST,UP,M-DOWN> mtu 1500 qdisc noqueue state LOWERLAYERDOWN mode DEFAULT group default qlen 1000
> > > >     link/ether b2:a9:c5:04:da:53 brd ff:ff:ff:ff:ff:ff
> > >
> > > I think that the commit log is confusing. It seems to say that
> > > the issue fixed is synchronizing state with hardware
> > > config change.
> > > But your example does not show any
> > > hardware change. Isn't this example really just
> > > a side effect of setting carrier off on close?
> >
> > The main goal for this patch is to make virtio-net follow RFC2863. The
> > main thing that is missed is to synchronize the operstate with admin
> > state, if we do this, we get several good results, one of the obvious
> > one is to allow virtio-net to propagate status to the upper layer, for
> > example if the admin state of the lower virtio-net is down it should
> > be propagated to the macvlan on top, so I give the example of using a
> > stacked device. I'm not we had others but the commit log is probably
> > too small to say all of it.
> 
> Michael, any more comments on this?
> 
> Thans

Still don't get it, sorry.
> > > > This is done by trying to toggle the carrier upon open/close and
> > > > synchronize with the config change work.
What does this sentence mean? What is not synchronized with config
change that needs to be?

> >
> > >
> > >
> > > > Cc: Venkat Venkatsubra <[email-masked]>
> > > > Cc: Gia-Khanh Nguyen <[email-masked]>
> > > > Signed-off-by: Jason Wang <[email-masked]>
> > >
> > > Yes but this just forces lots of re-reads of config on each
> > > open/close for no good reason.
> >
> > Does it really harm? Technically the link status could be changed
> > several times when the admin state is down as well.
> >
> > > Config interrupt is handled in core, you can read once
> > > on probe and then handle config changes.
> >
> > Per RFC2863, the code tries to avoid dealing with any operstate change
> > via config space read when the admin state is down.
> >
> > >
> > >
> > >
> > >
> > >
> > > > ---
> > > >  drivers/net/virtio_net.c | 64 ++++++++++++++++++++++++----------------
> > > >  1 file changed, 38 insertions(+), 26 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 0b4747e81464..e6626ba25b29 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -2476,6 +2476,25 @@ static void virtnet_cancel_dim(struct virtnet_info *vi, struct dim *dim)
> > > >       net_dim_work_cancel(dim);
> > > >  }
> > > >
> > > > +static void virtnet_update_settings(struct virtnet_info *vi)
> > > > +{
> > > > +     u32 speed;
> > > > +     u8 duplex;
> > > > +
> > > > +     if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX))
> > > > +             return;
> > > > +
> > > > +     virtio_cread_le(vi->vdev, struct virtio_net_config, speed, &speed);
> > > > +
> > > > +     if (ethtool_validate_speed(speed))
> > > > +             vi->speed = speed;
> > > > +
> > > > +     virtio_cread_le(vi->vdev, struct virtio_net_config, duplex, &duplex);
> > > > +
> > > > +     if (ethtool_validate_duplex(duplex))
> > > > +             vi->duplex = duplex;
> > > > +}
> > > > +
> > > >  static int virtnet_open(struct net_device *dev)
> > > >  {
> > > >       struct virtnet_info *vi = netdev_priv(dev);
> > > > @@ -2494,6 +2513,18 @@ static int virtnet_open(struct net_device *dev)
> > > >                       goto err_enable_qp;
> > > >       }
> > > >
> > > > +     if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> > > > +             virtio_config_driver_enable(vi->vdev);
> > > > +             /* Do not schedule the config change work as the
> > > > +              * config change notification might have been disabled
> > > > +              * by the virtio core. */
> > >
> > > I don't get why you need this.
> > > If the notification was disabled it will just trigger later.
> > > This is exactly why using core is a good idea.
> >
> > So we need a read here (this seems to be not rare for most modern
> > hardware NICs) because we don't know if the link status is changed or
> > not and it is not guaranteed by virtio_config_driver_enable() since it
> > only works when there's a pending config change. Another thing is that
> > the device is being freezed, so the virtio core may prevent the device
> > from accessing the device.
> >
> > So using virtio_config_changed() will guaranteed that:
> >
> > 1) if the device is not being freezed, it will read the config space soon
> > 2) if the device is being freezed, the read of the config space will
> > be delayed to resume
> >
> > >
> > >
> > > > +             virtio_config_changed(vi->vdev);
> > > > +     } else {
> > > > +             vi->status = VIRTIO_NET_S_LINK_UP;
> > > > +             virtnet_update_settings(vi);
> > >
> > >
> > > And why do we need this here I don't get at all.
> >
> > See above, because doing this on a probe is racy and buggy: The
> > opersate is up even if the adminstate is not, this is conflict with
> > RFC2863:
> >
> > "
> > If ifAdminStatus is down(2) then ifOperStatus
> >             should be down(2)
> > "
> >
> > >
> > > > +             netif_carrier_on(dev);
> > > > +     }
> > >
> > >
> > >
> > > > +
> > > >       return 0;
> > > >
> > > >  err_enable_qp:
> > > > @@ -2936,12 +2967,19 @@ static int virtnet_close(struct net_device *dev)
> > > >       disable_delayed_refill(vi);
> > > >       /* Make sure refill_work doesn't re-enable napi! */
> > > >       cancel_delayed_work_sync(&vi->refill);
> > > > +     /* Make sure config notification doesn't schedule config work */
> > > > +     virtio_config_driver_disable(vi->vdev);
> > > > +     /* Make sure status updating is cancelled */
> > > > +     cancel_work_sync(&vi->config_work);
> > > >
> > > >       for (i = 0; i < vi->max_queue_pairs; i++) {
> > > >               virtnet_disable_queue_pair(vi, i);
> > > >               virtnet_cancel_dim(vi, &vi->rq[i].dim);
> > > >       }
> > > >
> > > > +     vi->status &= ~VIRTIO_NET_S_LINK_UP;
> > > > +     netif_carrier_off(dev);
> > > > +
> > > >       return 0;
> > > >  }
> > > >
> > > > @@ -4640,25 +4678,6 @@ static void virtnet_init_settings(struct net_device *dev)
> > > >       vi->duplex = DUPLEX_UNKNOWN;
> > > >  }
> > > >
> > > > -static void virtnet_update_settings(struct virtnet_info *vi)
> > > > -{
> > > > -     u32 speed;
> > > > -     u8 duplex;
> > > > -
> > > > -     if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX))
> > > > -             return;
> > > > -
> > > > -     virtio_cread_le(vi->vdev, struct virtio_net_config, speed, &speed);
> > > > -
> > > > -     if (ethtool_validate_speed(speed))
> > > > -             vi->speed = speed;
> > > > -
> > > > -     virtio_cread_le(vi->vdev, struct virtio_net_config, duplex, &duplex);
> > > > -
> > > > -     if (ethtool_validate_duplex(duplex))
> > > > -             vi->duplex = duplex;
> > > > -}
> > > > -
> > > >  static u32 virtnet_get_rxfh_key_size(struct net_device *dev)
> > > >  {
> > > >       return ((struct virtnet_info *)netdev_priv(dev))->rss_key_size;
> > > > @@ -6000,13 +6019,6 @@ static int virtnet_probe(struct virtio_device *vdev)
> > > >       /* Assume link up if device can't report link status,
> > > >          otherwise get link status from config. */
> > > >       netif_carrier_off(dev);
> > > > -     if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> > > > -             schedule_work(&vi->config_work);
> > > > -     } else {
> > > > -             vi->status = VIRTIO_NET_S_LINK_UP;
> > > > -             virtnet_update_settings(vi);
> > > > -             netif_carrier_on(dev);
> > > > -     }
> > >
> > >
> > > Here it all made sense - we were reading config for the 1st time.
> >
> > See above.
> >
> > Thanks
> >
> > >
> > >
> > > >       for (i = 0; i < ARRAY_SIZE(guest_offloads); i++)
> > > >               if (virtio_has_feature(vi->vdev, guest_offloads[i]))
> > > > --
> > > > 2.31.1
> > >
> > >