On Mon, Feb 03, 2014 at 03:26:42PM +0100, Peter Zijlstra wrote: > On Mon, Feb 03, 2014 at 03:19:18PM +0100, Paolo Bonzini wrote: > > Il 03/02/2014 15:12, Peter Zijlstra ha scritto: > > >>> But why doesn't it crash on baremetal? > > >>> Probably baremetal simply returns 0 or something. > > >>> Let me try .. > > >The claim "v2 and above have FEATURE_PDCM" is in fact true for real > > >hardware. > > > > > >If it didn't the rdmsr() would have generated an exception and we'd have > > >crashed just like your virtual thingy did. > > > > Right, and the virt thingy has no PEBS, so there is no correct value that we > > could return from the MSR. That's why the CPUID bit is zero. > > There's more than PEBS in there, there's also the LBR format (which you > obviously also don't have) and the full_width_write bit, which you also > don't have. > > Returning 0 is a safe value. Seeing you don't have LBR, we don't look at > the LBR format fields, seeing you don't have PEBS, we don't look at > those fields either. > > We don't appear to use the SMM_FREEZE bit at all, and 0 is in fact the > right value for full_width_write, since you lack the MSRs to support > that. > > Anyway, its easy for me to make future kernels do the right PDCM test, > probably easy to backport too (should apply with minimal trouble back a > fair number of releases). > > You can also implement the MSR to simply return 0, which is a safe > value. OK, I'm testing the following now: ---> Subject: [PATCH] kvm: emulate MSR_IA32_PERF_CAPABILITIES guests expect that this does not crash if version > 1. Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> --- arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 5d004da..eaf5016 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2407,6 +2407,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata) /* CPU multiplier */ data |= (((uint64_t)4ULL) << 40); break; + case MSR_IA32_PERF_CAPABILITIES: + data = 0; + break; case MSR_EFER: data = vcpu->arch.efer; break; -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
