Linux Virtualization - Jun 2018 - [virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio_net

On Tue, 26 Jun 2018 04:50:25 +0300
"Michael S. Tsirkin" <mst at 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.
> 
So, what I get from this is that QEMU needs to be able to control all
of standby, uuid, and mac to accommodate the different setups
(respectively have libvirt/management software set it up). Is the host
able to find out respectively define whether a VF is trusted?

On Tue, Jun 26, 2018 at 05:17:32PM +0200, Cornelia Huck
wrote:
> On Tue, 26 Jun 2018 04:50:25 +0300
> "Michael S. Tsirkin" <mst at 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.
> > 
> 
> So, what I get from this is that QEMU needs to be able to control all
> of standby, uuid, and mac to accommodate the different setups
> (respectively have libvirt/management software set it up). Is the host
> able to find out respectively define whether a VF is trusted?
You do it with ip link I think but QEMU doesn't normally do this,
it relies on libvirt to poke at host kernel and supply the info.

-- 
MST

On Tue, 26 Jun 2018 18:38:51 +0300
"Michael S. Tsirkin" <mst at redhat.com> wrote:
> On Tue, Jun 26, 2018 at 05:17:32PM +0200, Cornelia Huck wrote:
> > On Tue, 26 Jun 2018 04:50:25 +0300
> > "Michael S. Tsirkin" <mst at 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.
> > >   
> > 
> > So, what I get from this is that QEMU needs to be able to control all
> > of standby, uuid, and mac to accommodate the different setups
> > (respectively have libvirt/management software set it up). Is the host
> > able to find out respectively define whether a VF is trusted?  
> 
> You do it with ip link I think but QEMU doesn't normally do this,
> it relies on libvirt to poke at host kernel and supply the info.
> 
Ok, that makes me conclude that we definitely need to involve the
libvirt folks before we proceed further with defining QEMU interfaces.