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Let me chip in on this as we are experiencing a similar issue:

We have started encountering this behaviour following a ubuntu trusty to
xenial upgrade (we are still running Mitaka). It affects VMs that
previously were successfully migrated cross architecture (xeon v2 ->
skylake and vice versa).
We are yet unable to pinpoint the exact cause because the issue is
difficult to reproduce: VMs started on the affected node migrate freely
and their xml is *identical* (except for UUIDs and such) to the one of
the VMs that refuse to migrate.

As a side note I think the key is the: "InvalidCPUInfo: Unacceptable CPU
info".
Normally, infact, the error would also include which are the problematic
flags and despite the exception coming always from driver.py the message
is different.

If anyone has any suggestions other than reboot the affected VMs I'll
gladly give them a try.

Best
Mattia

On 12/14/18 3:56 PM, Jonathan D. Proulx wrote:
> On Thu, Dec 13, 2018 at 06:48:10PM -0500, Erik McCormick wrote:
> :On Thu, Dec 13, 2018 at 5:37 PM Torin Woltjer
> :<torin.woltjer at granddial.com> wrote:
> :>
> :> Having issues getting live migrations to functions between two compute nodes.
> :> One is an Opteron G4 and the other is an Opteron G5. I can migrate from the G4 to the G5 just fine. When I try to migrate an instance from the G5 node to the G4 node I get an error message:
> :> InvalidCPUInfo: Unacceptable CPU info: CPU doesn't have compatibility.
> :> This is despite having the following setting in my /etc/nova/nova.conf on the G5 machine.
> :>
> :> [libvirt]
> :> cpu_mode = custom
> :> cpu_model = Opteron_G4
> :>
> :> Is this not the setting I'm looking for? What can I do to make this work?
> :>
> 
> :Did you create the instances you are trying to migrate after you
> :applied the setting? If not, do a cold migrate and then try the live
> :one again.
> 
> My bets are on this one, it's the sort of thing I do anyway. An
> `openstack server reboot --hard` should also recreate the VM inplace
> with new config settings I think.
> 
> you can double check that the instance you are trying to move has the
> correct CPU setting by looking at the libvirt XML, either in:
> 
> /var/lib/nova/instances/<instance uuid>/libvirt.xml
> 
> or dumping libvirt's info on running VM:
> 
> virsh dumpxml <virt instance-name>
> 
> what you don't want to see is:
> 
>   <cpu mode="host-passthrough" match="exact">
> 
> This is what I use and just live with somewhat complex mappings of
> what will move where because my user want all thw feature they can
> get.  So I'm not 100% sure what you wnat to see here, but I know it's
> not that.
> 
> -Jon
> 
> 


-- 
Mattia Belluco
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