Re: [PATCH v2] kvm: x86: emulate monitor and mwait instructions as nop

Michael S. Tsirkin
2014-06-04T19:08:04Z

On Wed, Jun 04, 2014 at 06:34:04PM +0200, Paolo Bonzini wrote:
> Il 04/06/2014 16:44, Alexander Graf ha scritto:
> >
> >
> >>Obviously, if you really like the current behavior better you can
> >>always reject whatever patch I'll come up with, but I'd like to at
> >>least try and see what it would look like :)
> >
> >I think it's perfectly fine to leave mwait always implemented as NOP -
> >it's valid behavior.
> >
> >As for the CPUID exposure, that should be a pure QEMU thing. If
> >overriding CPUID bits the kernel mask tells us doesn't work today, we
> >should just make it possible :).
>
> That should be the purpose of KVM_GET_EMULATED_CPUID, so MWAIT could be
> added in __do_cpuid_ent_emulated. However, the corresponding QEMU patches
> were never included. Borislav, can you refresh them?
>
> Paolo

I don't understand why would we want mwait bit set in CPUID.
The only reason we want the nop is because of broken guests which
don't check CPUID.

--
MST