Re: libvirt and nestedhvm.

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 06/06/14 14:28, Alvin Starr wrote:
> I am trying to shoehorn the ability to start a nested HVM into libvirt
> through the libxl interface.
>
> Setting the nestedhvm flag is easy enough but I also need to mask the
> svm_npt cpuid flags.

This presumably comes from a KVM centric view where the environment
running libvirtd is the host environment?

>
> This is where life gets interesting.
>
> LIbvirt seems to probe the CPUID registers to determine what flags are
> available.
> Libvirt then stops me from trying to mask the svm or npt flags since
> they are not visible in dom0.
>
> So my question is.
> Can I enable the svm,npt flags in dom0?

Technically it is possible to make these flags appear...

> Is there anything equivalent to nestedhvm for dom0?

... but being features that PV guests cannot possibly use, advertising
them is a bad idea.

>
> or is there a way to read the raw CPU flags?
>
Not really.

It is one of the many things on my bucketlist of basic things which need
fixing with all the other Xen/libxc/toolstack cpuid work.

~Andrew