Re: [PATCH][v2] kvm: x86: emulate APERF/MPERF registers

[Xiaoyao Li]

On 4/29/2020 1:46 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 we should emulate aperf mperf to achieve it

the period of aperf/mperf in guest mode are accumulated as
emulated value, and add per-VM knod to enable emulate mperfaperf

diff v1:
1. support AMD
2. support per-vm capability to enable

[...]

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 851e9cc79930..1d157a8dba46 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4310,6 +4310,12 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct 
msr_data *msr_info)
        case MSR_F10H_DECFG:
                msr_info->data = svm->msr_decfg;
                break;
+       case MSR_IA32_MPERF:
+               msr_info->data = vcpu->arch.v_mperf;
+               break;
+       case MSR_IA32_APERF:
+               msr_info->data = vcpu->arch.v_aperf;
+               break;
        default:
                return kvm_get_msr_common(vcpu, msr_info);
        }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 91749f1254e8..b05e276e262b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1914,6 +1914,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct 
msr_data *msr_info)
                    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
                        return 1;
                goto find_shared_msr;
+       case MSR_IA32_MPERF:
+               msr_info->data = vcpu->arch.v_mperf;
+               break;
+       case MSR_IA32_APERF:
+               msr_info->data = vcpu->arch.v_aperf;
+               break;

They are same for both vmx and svm, you can put them in kvm_get_msr_common()

BTW, are those two MSR always readable regardless of guest's CPUID?

        default:
        find_shared_msr:
                msr = find_msr_entry(vmx, msr_info->index);