Re: [PATCH v5 10/16] KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled

[Xu, Like]

On 2021/4/20 16:30, Liuxiangdong wrote:
> On 2021/4/15 11:20, Like Xu wrote:
> > The bit 12 represents "Processor Event Based Sampling Unavailable (RO)" :
> >     1 = PEBS is not supported.
> >     0 = PEBS is supported.
> >
> > A write to this PEBS_UNAVL available bit will bring #GP(0) when guest PEBS
> > is enabled. Some PEBS drivers in guest may care about this bit.
> >
> > Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/vmx/pmu_intel.c | 2 ++
> >   arch/x86/kvm/x86.c           | 4 ++++
> >   2 files changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> > index 58f32a55cc2e..c846d3eef7a7 100644
> > --- a/arch/x86/kvm/vmx/pmu_intel.c
> > +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > @@ -588,6 +588,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
> >           bitmap_set(pmu->all_valid_pmc_idx, INTEL_PMC_IDX_FIXED_VLBR, 1);
> >         if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_FORMAT) {
> > +        vcpu->arch.ia32_misc_enable_msr &= 
> > ~MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
> >           if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_BASELINE) {
> >               pmu->pebs_enable_mask = ~pmu->global_ctrl;
> >               pmu->reserved_bits &= ~ICL_EVENTSEL_ADAPTIVE;
> > @@ -597,6 +598,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
> >               }
> >               pmu->pebs_data_cfg_mask = ~0xff00000full;
> >           } else {
> > +            vcpu->arch.ia32_misc_enable_msr |= 
> > MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
> >               pmu->pebs_enable_mask =
> >                   ~((1ull << pmu->nr_arch_gp_counters) - 1);
> >           }
>
> I guess what we want is
>
>        if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_FORMAT) {
>                vcpu->arch.ia32_misc_enable_msr &= 
> ~MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
>                if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_BASELINE) {
>                        pmu->pebs_enable_mask = ~pmu->global_ctrl;
>                        pmu->reserved_bits &= ~ICL_EVENTSEL_ADAPTIVE;
>                        for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
>                                pmu->fixed_ctr_ctrl_mask &=
>                                        ~(1ULL << (INTEL_PMC_IDX_FIXED + i 
> * 4));
>                        }
>                        pmu->pebs_data_cfg_mask = ~0xff00000full;
>                } else {
>                        pmu->pebs_enable_mask =
>                                ~((1ull << pmu->nr_arch_gp_counters) - 1);
>                }
>        } else {
>                vcpu->arch.ia32_misc_enable_msr |= 
> MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
>                vcpu->arch.perf_capabilities &= ~PERF_CAP_PEBS_MASK;
>        }
>
>
> But here is
>
>        if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_FORMAT) {
>                vcpu->arch.ia32_misc_enable_msr &= 
> ~MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;
>                if (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_BASELINE) {
>                        pmu->pebs_enable_mask = ~pmu->global_ctrl;
>                        pmu->reserved_bits &= ~ICL_EVENTSEL_ADAPTIVE;
>                        for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
>                                pmu->fixed_ctr_ctrl_mask &=
>                                        ~(1ULL << (INTEL_PMC_IDX_FIXED + i 
> * 4));
>                        }
>                        pmu->pebs_data_cfg_mask = ~0xff00000full;
>                } else {
>                        vcpu->arch.ia32_misc_enable_msr |= 
> MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL;

You got me. The v5 is wrong here but v4 is right.

Please let me know if you have more comments on this version.

> pmu->pebs_enable_mask =
>                                ~((1ull << pmu->nr_arch_gp_counters) - 1);
>                }
>        } else {
>                vcpu->arch.perf_capabilities &= ~PERF_CAP_PEBS_MASK;
>        }
>
>
> Wrong else branch?
>
>
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 1a64e816e06d..ed38f1dada63 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -3126,6 +3126,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, 
> > struct msr_data *msr_info)
> >           break;
> >       case MSR_IA32_MISC_ENABLE:
> >           data &= ~MSR_IA32_MISC_ENABLE_EMON;
> > +        if (!msr_info->host_initiated &&
> > +            (vcpu->arch.perf_capabilities & PERF_CAP_PEBS_FORMAT) &&
> > +            (data & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL))
> > +            return 1;
> >           if (!kvm_check_has_quirk(vcpu->kvm, 
> > KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT) &&
> >               ((vcpu->arch.ia32_misc_enable_msr ^ data) & 
> > MSR_IA32_MISC_ENABLE_MWAIT)) {
> >               if (!guest_cpuid_has(vcpu, X86_FEATURE_XMM3))