[virt-tools-list] [virt-manager PATCH 0/8] cpu related bug fixes and improvements

[Hetz Ben Hamo]

> > Out of curiosity, I got 2 questions:
>
> Hi
>
> > 1. Where does the domcapabilities are being retrieved from?
>
> You can get it by running 'virsh domcapabilities', it has some
> parameters that can change the output, look for domcapabilities
> in 'man virsh'.
>
> To extend the answer, the data are provided by libvirt and libvirt
> gets the data from QEMU (libvirt >= 3.2.0 and QEMU >= 2.9.0) or from
> it's own database and cpuid.
>

Ok.


> > 2. Is is possible to change some flags (in the CPU section) from
> 'require'
> > to disable and vice versa? (i'm talking system wide, not per VM) if so,
> how?
>
> No, these domcapabilities returns what is possible with specific QEMU
> on specific host.  If you want to disable some features or enable them
> you need to specify that for every singe VM.
>
> My question is why would you like to change the CPU features?
>
> I'm tracking an issue with AMD's Zen/Zen+ based processors.
The "monitor" CPU flag is not being exposed in nested virtualization in the
guest OS. I tried it with Hyper-V, ESXi, and XenServer as well as KVM.

With Libvirt - it is, indeed, being disabled and this behavior is correct:

virsh domcapabilities | grep monitor
     <feature policy='disable' name='monitor'/>

However, when trying to use oVirt in nested virtualization with any AMD
Zen/Zen+ based CPU, it doesn't let create or run any VM and it complains
about "monitor" is missing, and I'm trying to figure out who needs to fix
the code, either oVirt or the KVM devs. That's why I wanted to see if it's
an error or not.

Thanks,
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