Re: KVM PMU virtualization

[Ingo Molnar <mingo@elte.hu>]

* Jes Sorensen <Jes.Sorensen@redhat.com> wrote:

> On 02/26/10 12:06, Joerg Roedel wrote:
>
> > Isn't there a cpuid bit indicating the availability of architectural 
> > perfmon?
> 
> Nope, the perfmon flag is a fake Linux flag, set based on the contents on 
> cpuid 0x0a

There is a way to query the CPU for 'architectural perfmon' though, via CPUID 
alone - that is how we set the X86_FEATURE_ARCH_PERFMON shortcut. The logic 
is:

        if (c->cpuid_level > 9) {
                unsigned eax = cpuid_eax(10);
                /* Check for version and the number of counters */
                if ((eax & 0xff) && (((eax>>8) & 0xff) > 1))
                        set_cpu_cap(c, X86_FEATURE_ARCH_PERFMON);
        }

But emulating that doesnt solve the problem: as OSs generally dont key their 
PMU drivers off the relatively new 'architectural perfmon' CPUID detail, but 
based on much higher level CPUID attributes. (like Intel/AMD)

	Ingo