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

["Li,Rongqing" <lirongqing@baidu.com>]

> -----邮件原件-----
> 发件人: Paolo Bonzini [mailto:pbonzini@redhat.com]
> 发送时间: 2020年4月29日 18:21
> 收件人: Peter Zijlstra <peterz@infradead.org>; Li,Rongqing
> <lirongqing@baidu.com>
> 抄送: linux-kernel@vger.kernel.org; kvm@vger.kernel.org; x86@kernel.org;
> hpa@zytor.com; bp@alien8.de; mingo@redhat.com; tglx@linutronix.de;
> joro@8bytes.org; jmattson@google.com; wanpengli@tencent.com;
> vkuznets@redhat.com; sean.j.christopherson@intel.com
> 主题: Re: [PATCH][v2] kvm: x86: emulate APERF/MPERF registers
> 
> On 29/04/20 10:54, Peter Zijlstra wrote:
> > On Wed, Apr 29, 2020 at 01:46:36PM +0800, 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
> > Would it make sense to provide a pass-through APERF/MPERF for
> > KVM_HINTS_REALTIME ? Because that hint guarantees we have a 1:1
> > vCPU:CPU binding and guaranteed no over-commit.
> >
> 
> Yes but that's up to userspace.
> 
> Paolo

Seem kernel should give the capability to userspace to disable the intercept mperf/aperf for KVM_HINTS_REALTIME

So I will change this patch to support three mode mperfaperf:  none, software emulate, and pt


diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1d157a8dba46..6b05f78bde78 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1657,9 +1657,11 @@ static void init_vmcb(struct vcpu_svm *svm)
        set_intercept(svm, INTERCEPT_SKINIT);
        set_intercept(svm, INTERCEPT_WBINVD);
        set_intercept(svm, INTERCEPT_XSETBV);
-       set_intercept(svm, INTERCEPT_RDPRU);
        set_intercept(svm, INTERCEPT_RSM);
 
+       if (!guest_mperfaperf_pt(svm->vcpu.kvm))
+               set_intercept(svm, INTERCEPT_RDPRU);
+
        if (!kvm_mwait_in_guest(svm->vcpu.kvm)) {
                set_intercept(svm, INTERCEPT_MONITOR);
                set_intercept(svm, INTERCEPT_MWAIT);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b05e276e262b..231732924c50 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6765,6 +6765,12 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
                vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
                vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
        }
+
+       if (guest_mperfaperf_pt(vcpu->kvm)) {
+               vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_MPERF, MSR_TYPE_R);
+               vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_APERF, MSR_TYPE_R);
+       }
+
        vmx->msr_bitmap_mode = 0;
 
        vmx->loaded_vmcs = &vmx->vmcs01;


-Li