[libvirt] exposing host-passthrough in virt-manager ui? (was: Re: [virt-tools-list] small suggestion)

[Cole Robinson]

On 2/6/19 10:57 AM, Pavel Hrdina wrote:
> On Wed, Feb 06, 2019 at 10:20:38AM -0500, Cole Robinson wrote:
>> On 2/5/19 6:19 PM, Hetz Ben Hamo wrote:
>>> Is it possible to add in the virt-manager the "host-passthrough" to the
>>> CPU models please?
>>>
>>
>> You can type 'host-passthrough' into the field and it will work. The reason
>> we don't advertise it is because it's considered to have some mild
>> supportability issues with libvirt. For the vast majority of use cases
>> though it's completely fine
> 
> Maybe we can reconsider this decision, the only thing that would not
> work is live migration to destination with different CPU and we can
> have a warning/info about it in the UI.
> 
> Possibly we could allow to set 'host-passthrough' as the default guest
> CPU in virt-manager config.
> 

Nowadays with host-model being much smarter, is there much functional 
difference between host-model and host-passthrough? I don't really know 
the answer.

> Most workstation/desktop users of virt-manager probably doesn't care
> about live migration and it would copy the host CPU as closely as
> possible.  Since we allow to manually type in 'host-passthrough' I
> personally don't see any reason why it cannot be selectable.
> 

The problem I see is that host-passthrough sets the libvirt 'taint' flag 
on the VM. While it doesn't have any real impact on end users generally 
I took that to mean 'you are doing something that is unsupported'.

I don't personally don't have strong feelings against it but I've just 
followed the advice I've been given here. Things have changed quite a 
bit in the cpu config space in the past few years so maybe things are 
different. changing subject and ccing libvir-list for wider audience

Thanks,
Cole