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

[Siwei Liu <loseweigh@gmail.com>]

On Tue, Jun 26, 2018 at 5:29 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Tue, Jun 26, 2018 at 04:38:26PM -0700, Siwei Liu wrote:
>> On Mon, Jun 25, 2018 at 6:50 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
>> > 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.
>>
>> That's why I think pairing using MAC is fragile IMHO. When VF's MAC
>> got changed before virtio attempts to match and pair the device, it
>> ends up with no pairing found out at all.
>
> Guest seems to match on the hardware mac and ignore whatever
> is set by user. Makes sense to me and should not be fragile.
Host can change the hardware mac for VF any time.

-Siwei
>
>
>> UUID is better.
>>
>> -Siwei
>>
>> >
>> > --
>> > MST