Re: [PATCH 3/3] KVM: x86: correct mwait and monitor emulation

Gabriel L. Somlo
2014-06-18T18:59:44Z

On Wed, Jun 18, 2014 at 11:30:07AM -0700, Eric Northup wrote:
> Quoting Gabriel's post http://www.spinics.net/lists/kvm/msg103792.html :
>
> [...]
>
> > E.g., OS X 10.5 *does* check CPUID, and panics if it doesn't find it.
> > It needs the MONITOR cpuid flag to be on, *and* the actual
> > instructions to work.

That was an argument in favor of finding a mechanism to allow (qemu)
users to enable an otherwise default-off monitor cpuid flag.

We definitely don't want to advertise monitor/mwait availability to
guests which would otherwise sanely fail back to a hlt-based idle loop
when cpuid tells them monitor/mwait are not available :)

However, check my earlier proposal of backing out of monitor/mwait
entirely (as it turns out, there's a kernel command line to tell OS X
not to use monitor/mwait, which is IMHO vastly preferable to creating
"undocumented" KVM hacks :)

Thanks much,
--Gabriel