Re: [PATCH v2 24/54] KVM: x86/pmu: Create a function prototype to disable MSR interception

Mingwei Zhang
2024-05-30T05:24:10Z

On Wed, May 08, 2024, Chen, Zide wrote:
>
>
> On 5/5/2024 10:29 PM, Mingwei Zhang wrote:
> > Add one extra pmu function prototype in kvm_pmu_ops to disable PMU MSR
> > interception.
> >
> > Signed-off-by: Mingwei Zhang <mizhang@google.com>
> > Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> > ---
> > arch/x86/include/asm/kvm-x86-pmu-ops.h | 1 +
> > arch/x86/kvm/cpuid.c | 4 ++++
> > arch/x86/kvm/pmu.c | 5 +++++
> > arch/x86/kvm/pmu.h | 2 ++
> > 4 files changed, 12 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm-x86-pmu-ops.h b/arch/x86/include/asm/kvm-x86-pmu-ops.h
> > index fd986d5146e4..1b7876dcb3c3 100644
> > --- a/arch/x86/include/asm/kvm-x86-pmu-ops.h
> > +++ b/arch/x86/include/asm/kvm-x86-pmu-ops.h
> > @@ -24,6 +24,7 @@ KVM_X86_PMU_OP(is_rdpmc_passthru_allowed)
> > KVM_X86_PMU_OP_OPTIONAL(reset)
> > KVM_X86_PMU_OP_OPTIONAL(deliver_pmi)
> > KVM_X86_PMU_OP_OPTIONAL(cleanup)
> > +KVM_X86_PMU_OP_OPTIONAL(passthrough_pmu_msrs)
> >
> > #undef KVM_X86_PMU_OP
> > #undef KVM_X86_PMU_OP_OPTIONAL
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index 77352a4abd87..b577ba649feb 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -381,6 +381,10 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> > vcpu->arch.reserved_gpa_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu);
> >
> > kvm_pmu_refresh(vcpu);
> > +
> > + if (is_passthrough_pmu_enabled(vcpu))
> > + kvm_pmu_passthrough_pmu_msrs(vcpu);
> > +
> > vcpu->arch.cr4_guest_rsvd_bits =
> > __cr4_reserved_bits(guest_cpuid_has, vcpu);
> >
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index 3afefe4cf6e2..bd94f2d67f5c 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -1059,3 +1059,8 @@ int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp)
> > kfree(filter);
> > return r;
> > }
> > +
> > +void kvm_pmu_passthrough_pmu_msrs(struct kvm_vcpu *vcpu)
> > +{
> > + static_call_cond(kvm_x86_pmu_passthrough_pmu_msrs)(vcpu);
> > +}
>
> Don't quite understand why a separate callback is needed. It seems it's
> not messier if put this logic in the kvm_x86_vcpu_after_set_cpuid()
> callback.

One of the key point here is whether we _can_ intercept RDPMC. We have
to intercept it if there is _any_ counters / MSRs that is accessible by
rdmpc. In Intel CPU, the PERF_METRICS MSR is accessible from RDPMC. This
MSR is a vendor specific one. So that's why we added another vendor API.

Thanks.
-Mingwei