From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: KVM PMU virtualization
Date: Fri, 26 Feb 2010 12:24:04 +0100
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Cc: Joerg Roedel <joro@8bytes.org>, Avi Kivity <avi@redhat.com>,
	KVM General <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Zachary Amsden <zamsden@redhat.com>,
	Gleb Natapov <gleb@redhat.com>, ming.m.lin@intel.com,
	"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Arjan van de Ven <arjan@infradead.org>,
	Fr??d??ric Weisbecker <fweisbec@gmail.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>
To: Jes Sorensen <Jes.Sorensen@redhat.com>
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* 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