netdev - Re: [virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio

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Date:   Tue, 26 Jun 2018 04:50:25 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     Siwei Liu <loseweigh@...il.com>, Cornelia Huck <cohuck@...hat.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        virtio-dev@...ts.oasis-open.org, aaron.f.brown@...el.com,
        Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kubakici@...pl>,
        Netdev <netdev@...r.kernel.org>, qemu-devel@...gnu.org,
        virtualization@...ts.linux-foundation.org, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com,
        Joao Martins <joao.m.martins@...cle.com>,
        Venu Busireddy <venu.busireddy@...cle.com>,
        vijay.balakrishna@...cle.com
Subject: Re: [virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce
 VIRTIO_NET_F_STANDBY feature bit to virtio_net

On Mon, Jun 25, 2018 at 10:54:09AM -0700, Samudrala, Sridhar wrote:
> > > > > Might not neccessarily be something wrong, but it's very limited to
> > > > > prohibit the MAC of VF from changing when enslaved by failover.
> > > > You mean guest changing MAC? I'm not sure why we prohibit that.
> > > I think Sridhar and Jiri might be better person to answer it. My
> > > impression was that sync'ing the MAC address change between all 3
> > > devices is challenging, as the failover driver uses MAC address to
> > > match net_device internally.
> 
> Yes. The MAC address is assigned by the hypervisor and it needs to manage the movement
> of the MAC between the PF and VF.  Allowing the guest to change the MAC will require
> synchronization between the hypervisor and the PF/VF drivers. Most of the VF drivers
> don't allow changing guest MAC unless it is a trusted VF.

OK but it's a policy thing. Maybe it's a trusted VF. Who knows?
For example I can see host just
failing VIRTIO_NET_CTRL_MAC_ADDR_SET if it wants to block it.
I'm not sure why VIRTIO_NET_F_STANDBY has to block it in the guest.

-- 
MST