Subject: Re: [PATCH net-next V2] virtio-net: synchronize operstate with admin state on up/down

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 20 Jun 2024 01:58:40 -0400

On Thu, Jun 06, 2024 at 08:22:13AM +0800, Jason Wang wrote:
> On Fri, May 31, 2024 at 8:18 AM Jason Wang <[email-masked]> wrote:
> >
> > On Thu, May 30, 2024 at 9:09 PM Michael S. Tsirkin <[email-masked]> wrote:
> > >
> > > On Thu, May 30, 2024 at 06:29:51PM +0800, Jason Wang wrote:
> > > > On Thu, May 30, 2024 at 2:10 PM Michael S. Tsirkin <[email-masked]> wrote:
> > > > >
> > > > > On Thu, May 30, 2024 at 11:20:55AM +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
> > > > > >
> > > > > > Cc: Venkat Venkatsubra <[email-masked]>
> > > > > > Cc: Gia-Khanh Nguyen <[email-masked]>
> > > > > > Reviewed-by: Xuan Zhuo <[email-masked]>
> > > > > > Acked-by: Michael S. Tsirkin <[email-masked]>
> > > > > > Signed-off-by: Jason Wang <[email-masked]>
> > > > > > ---
> > > > > > Changes since V1:
> > > > > > - rebase
> > > > > > - add ack/review tags
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > > ---
> > > > > >  drivers/net/virtio_net.c | 94 +++++++++++++++++++++++++++-------------
> > > > > >  1 file changed, 63 insertions(+), 31 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > > index 4a802c0ea2cb..69e4ae353c51 100644
> > > > > > --- a/drivers/net/virtio_net.c
> > > > > > +++ b/drivers/net/virtio_net.c
> > > > > > @@ -433,6 +433,12 @@ struct virtnet_info {
> > > > > >       /* The lock to synchronize the access to refill_enabled */
> > > > > >       spinlock_t refill_lock;
> > > > > >
> > > > > > +     /* Is config change enabled? */
> > > > > > +     bool config_change_enabled;
> > > > > > +
> > > > > > +     /* The lock to synchronize the access to config_change_enabled */
> > > > > > +     spinlock_t config_change_lock;
> > > > > > +
> > > > > >       /* Work struct for config space updates */
> > > > > >       struct work_struct config_work;
> > > > > >
> > > > >
> > > > >
> > > > > But we already have dev->config_lock and dev->config_enabled.
> > > > >
> > > > > And it actually works better - instead of discarding config
> > > > > change events it defers them until enabled.
> > > > >
> > > >
> > > > Yes but then both virtio-net driver and virtio core can ask to enable
> > > > and disable and then we need some kind of synchronization which is
> > > > non-trivial.
> > >
> > > Well for core it happens on bring up path before driver works
> > > and later on tear down after it is gone.
> > > So I do not think they ever do it at the same time.
> >
> > For example, there could be a suspend/resume when the admin state is down.
> >
> > >
> > >
> > > > And device enabling on the core is different from bringing the device
> > > > up in the networking subsystem. Here we just delay to deal with the
> > > > config change interrupt on ndo_open(). (E.g try to ack announce is
> > > > meaningless when the device is down).
> > > >
> > > > Thanks
> > >
> > > another thing is that it is better not to re-read all config
> > > on link up if there was no config interrupt - less vm exits.
> >
> > Yes, but it should not matter much as it's done in the ndo_open().
> 
> Michael, any more comments on this?
> 
> Please confirm if this patch is ok or not. If you prefer to reuse the
> config_disable() I can change it from a boolean to a counter that
> allows to be nested.
> 
> Thanks

I think doing this in core and re-using config_lock is a cleaner approach for sure, yes.

For remove we do not need stacking. But yes we need it for freeze.

I am not sure how will a counter work. Let's see the patch.

It might be easier, besides config_enabled, to add config_disabled,
document that  config_enabled is controlled by core,
config_disabled by driver.
And we'd have 2 APIs virtio_config_disable_core and
virtio_config_disable_driver.

But I leave that decision in your capable hands.

> > Thanks
> > > --
> > > MST