Re: [PATCH 7/9] KVM: Expose the architectural performance monitoring CPUID leaf

[Gleb Natapov <gleb@redhat.com>]

On Tue, Nov 01, 2011 at 09:49:27AM -0600, David Ahern wrote:
> On 10/30/2011 10:53 AM, Gleb Natapov wrote:
> > From: Avi Kivity <avi@redhat.com>
> > 
> > Provide a CPUID leaf that describes the emulated PMU.
> > 
> > Signed-off-by: Avi Kivity <avi@redhat.com>
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > ---
> >  arch/x86/kvm/x86.c |   23 ++++++++++++++++++++++-
> >  1 files changed, 22 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 5ea4cb8..56153a9 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2543,6 +2543,28 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> >  	}
> >  	case 9:
> >  		break;
> > +	case 0xa: { /* Architectural Performance Monitoring */
> > +		struct x86_pmu_capability cap;
> > +
> > +		perf_get_x86_pmu_capability(&cap);
> > +
> > +		/*
> > +		 * Only support guest architectural pmu on a host
> > +		 * with architectural pmu.
> > +		 */
> > +		if (!cap.version)
> > +			memset(&cap, 0, sizeof(cap));
> > +
> > +		entry->eax = min(cap.version, 2)
> > +			| (cap.num_counters_gp << 8)
> > +			| (cap.bit_width_gp << 16)
> > +			| (cap.events_mask_len << 24);
> > +		entry->ebx = cap.events_mask;
> > +		entry->ecx = 0;
> > +		entry->edx = cap.num_counters_fixed
> > +			| (cap.bit_width_fixed << 5);
> > +		break;
> > +	}
> 
> If PERF_EVENTS is disabled in the host kernel will KVM return the right
> thing for the guest that might have PERF_EVENTS enabled?
> 
With correct implementation of perf_get_x86_pmu_capability() it should.
PERF_EVENTS disable version should set cap.version to zero, so guest will
find that vcpu does not provide architectural PMU.

> David
> 
> 
> >  	/* function 0xb has additional index. */
> >  	case 0xb: {
> >  		int i, level_type;
> > @@ -2637,7 +2659,6 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> >  	case 3: /* Processor serial number */
> >  	case 5: /* MONITOR/MWAIT */
> >  	case 6: /* Thermal management */
> > -	case 0xA: /* Architectural Performance Monitoring */
> >  	case 0x80000007: /* Advanced power management */
> >  	case 0xC0000002:
> >  	case 0xC0000003:

--
			Gleb.