Re: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers

[Paolo Bonzini]

On 24/04/20 18:25, Jim Mattson wrote:
>> Assuming we're going forward with this, at an absolute minimum the RDMSRs
>> need to be wrapped with checks on host _and_ guest support for the emulated
>> behavior.  Given the significant overhead, this might even be something
>> that should require an extra opt-in from userspace to enable.
> 
> I would like to see performance data before enabling this unconditionally.

I wouldn't want this to be enabled unconditionally anyway, because you
need to take into account live migration to and from processors that do
not have APERF/MPERF support.

Paolo