From: Wanpeng Li <wanpengli@xxxxxxxxxxx> PMU is not exposed to guest by most of products from cloud providers since the bad performance of PMU emulation and security concern. However, it calls perf_guest_switch_get_msrs() and clear_atomic_switch_msr() unconditionally even if PMU is not exposed to the guest before each vmentry. ~2% vmexit time reduced can be observed by kvm-unit-tests/vmexit.flat on my SKX server. Before patch: vmcall 1559 After patch: vmcall 1529 Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> --- v1 -> v2: * move the check before atomic_switch_perf_msrs arch/x86/kvm/vmx/vmx.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 40b1e61..b20423c 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6567,7 +6567,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) pt_guest_enter(vmx); - atomic_switch_perf_msrs(vmx); + if (vcpu_to_pmu(vcpu)->version) + atomic_switch_perf_msrs(vmx); atomic_switch_umwait_control_msr(vmx); if (enable_preemption_timer) -- 2.7.4
