Messages in this thread | | | Subject | Re: [PATCH][v5] KVM: X86: support APERF/MPERF registers | From | Xiaoyao Li <> | Date | Sat, 30 May 2020 18:40:13 +0800 |
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On 5/30/2020 12:35 PM, Li RongQing wrote: > Guest kernel reports a fixed cpu frequency in /proc/cpuinfo, > this is confused to user when turbo is enable, and aperf/mperf > can be used to show current cpu frequency after 7d5905dc14a > "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)" > so guest should support aperf/mperf capability > > This patch implements aperf/mperf by three mode: none, software > emulation, and pass-through > > None: default mode, guest does not support aperf/mperf > > Software emulation: the period of aperf/mperf in guest mode are > accumulated as emulated value > > Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because > that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed > no over-commit. > > And a per-VM capability is added to configure aperfmperf mode >
[...]
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index cd708b0b460a..c960dda4251b 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -122,6 +122,14 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu) > MSR_IA32_MISC_ENABLE_MWAIT); > } > > + best = kvm_find_cpuid_entry(vcpu, 6, 0); > + if (best) { > + if (guest_has_aperfmperf(vcpu->kvm) && > + boot_cpu_has(X86_FEATURE_APERFMPERF)) > + best->ecx |= 1; > + else > + best->ecx &= ~1; > + }
In my understanding, KVM allows userspace to set a CPUID feature bit for guest even if hardware doesn't support the feature.
So what makes X86_FEATURE_APERFMPERF different here? Is there any concern I miss?
-Xiaoyao
> /* Note, maxphyaddr must be updated before tdp_level. */ > vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu); > vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
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