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);
