netdev - Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when available

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Message-ID: <20171220162919.5618baa9@cakuba.netronome.com>
Date:   Wed, 20 Dec 2017 16:29:19 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Sridhar Samudrala <sridhar.samudrala@...el.com>,
        stephen@...workplumber.org, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        alexander.duyck@...il.com
Subject: Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when
 available

On Thu, 21 Dec 2017 02:15:31 +0200, Michael S. Tsirkin wrote:
> On Wed, Dec 20, 2017 at 02:33:34PM -0800, Jakub Kicinski wrote:
> > On Mon, 18 Dec 2017 16:40:36 -0800, Sridhar Samudrala wrote:  
> > > +static int virtio_netdev_event(struct notifier_block *this,
> > > +			       unsigned long event, void *ptr)
> > > +{
> > > +	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
> > > +
> > > +	/* Skip our own events */
> > > +	if (event_dev->netdev_ops == &virtnet_netdev)
> > > +		return NOTIFY_DONE;  
> > 
> > I wonder how does this work WRT loop prevention.  What if I have two
> > virtio devices with the same MAC, what is preventing them from claiming
> > each other?  Is it only the check above (not sure what is "own" in
> > comment referring to)?  
> 
> I expect we will add a feature bit (VIRTIO_NET_F_MASTER) and it will
> be host's responsibility not to add more than 1 such device.

Do you mean a virtio_net feature bit?  That won't stop the loop with
a hyperv device.  Unless we want every paravirt device to have such
bit and enforce there can be only one magic bond enslavement active in
the system.

Making the bonding information separate from the slaves seems so much
cleaner...  No limitation on device types, or how many bonds user
chooses to create.  No MAC matching...

> > I'm worried the check above will not stop virtio from enslaving hyperv
> > interfaces and vice versa, potentially leading to a loop, no?  There is
> > also the fact that it would be preferable to share the code between
> > paravirt drivers, to avoid duplicated bugs.
> > 
> > My suggestion during the previous discussion was to create a paravirt
> > bond device, which will explicitly tell the OS which interfaces to
> > bond, regardless of which driver they're using.  Could be some form of
> > ACPI/FW driver too, I don't know enough about x86 FW to suggest
> > something fully fleshed :(