| Message ID | 20240126085444.324918-27-xiong.y.zhang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/pmu: Introduce passthrough vPM | expand |
On Fri, Jan 26, 2024, Xiong Zhang wrote: > From: Mingwei Zhang <mizhang@google.com> > > Add host_perf_cap field in kvm_caps to record host PMU capability. This > helps KVM recognize the PMU capability difference between host and guest. > This awareness improves performance in PMU context switch. In particular, > KVM will need to zero out all MSRs that guest PMU does not use but host PMU > does use. Having the host PMU feature set cached in host_perf_cap in > kvm_caps structure saves a rdmsrl() to IA32_PERF_CAPABILITY MSR on each PMU > context switch. In addition, this is more convenient approach than open > another API on the host perf subsystem side. > > Signed-off-by: Mingwei Zhang <mizhang@google.com> > --- > arch/x86/kvm/vmx/vmx.c | 17 +++++++++-------- > arch/x86/kvm/x86.h | 1 + > 2 files changed, 10 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 349954f90fe9..50100954cd92 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -7896,32 +7896,33 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) > vmx_update_exception_bitmap(vcpu); > } > > -static u64 vmx_get_perf_capabilities(void) > +static void vmx_get_perf_capabilities(void) > { > u64 perf_cap = PMU_CAP_FW_WRITES; > struct x86_pmu_lbr lbr; > - u64 host_perf_cap = 0; > + > + kvm_caps.host_perf_cap = 0; > > if (!enable_pmu) > - return 0; > + return; > > if (boot_cpu_has(X86_FEATURE_PDCM)) > - rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap); > + rdmsrl(MSR_IA32_PERF_CAPABILITIES, kvm_caps.host_perf_cap); I would strongly prefer KVM snapshot the host's MSR_IA32_PERF_CAPABILITIES, if the CPU has PDMC, i.e. not leave it zero if the PMU is disabled. > > if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR) && > !enable_passthrough_pmu) { > x86_perf_get_lbr(&lbr); > if (lbr.nr) > - perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT; > + perf_cap |= kvm_caps.host_perf_cap & PMU_CAP_LBR_FMT; > } > > if (vmx_pebs_supported() && !enable_passthrough_pmu) { > - perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK; > + perf_cap |= kvm_caps.host_perf_cap & PERF_CAP_PEBS_MASK; > if ((perf_cap & PERF_CAP_PEBS_FORMAT) < 4) > perf_cap &= ~PERF_CAP_PEBS_BASELINE; > } > > - return perf_cap; > + kvm_caps.supported_perf_cap = perf_cap; > } > > static __init void vmx_set_cpu_caps(void) > @@ -7946,7 +7947,7 @@ static __init void vmx_set_cpu_caps(void) > > if (!enable_pmu) > kvm_cpu_cap_clear(X86_FEATURE_PDCM); > - kvm_caps.supported_perf_cap = vmx_get_perf_capabilities(); > + vmx_get_perf_capabilities(); > > if (!enable_sgx) { > kvm_cpu_cap_clear(X86_FEATURE_SGX); > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > index 38b73e98eae9..a29eb0469d7e 100644 > --- a/arch/x86/kvm/x86.h > +++ b/arch/x86/kvm/x86.h > @@ -28,6 +28,7 @@ struct kvm_caps { > u64 supported_mce_cap; > u64 supported_xcr0; > u64 supported_xss; > + u64 host_perf_cap; > u64 supported_perf_cap; This is confusing, host_perf_cap doesn't track "capabilities" so much as it tracks a raw host value. Luckily, I have a series that I am going to post this week that adds another struct for tracking host values, e.g. host_xss, host_efer, etc. > }; > > -- > 2.34.1 >
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 349954f90fe9..50100954cd92 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7896,32 +7896,33 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) vmx_update_exception_bitmap(vcpu); } -static u64 vmx_get_perf_capabilities(void) +static void vmx_get_perf_capabilities(void) { u64 perf_cap = PMU_CAP_FW_WRITES; struct x86_pmu_lbr lbr; - u64 host_perf_cap = 0; + + kvm_caps.host_perf_cap = 0; if (!enable_pmu) - return 0; + return; if (boot_cpu_has(X86_FEATURE_PDCM)) - rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap); + rdmsrl(MSR_IA32_PERF_CAPABILITIES, kvm_caps.host_perf_cap); if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR) && !enable_passthrough_pmu) { x86_perf_get_lbr(&lbr); if (lbr.nr) - perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT; + perf_cap |= kvm_caps.host_perf_cap & PMU_CAP_LBR_FMT; } if (vmx_pebs_supported() && !enable_passthrough_pmu) { - perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK; + perf_cap |= kvm_caps.host_perf_cap & PERF_CAP_PEBS_MASK; if ((perf_cap & PERF_CAP_PEBS_FORMAT) < 4) perf_cap &= ~PERF_CAP_PEBS_BASELINE; } - return perf_cap; + kvm_caps.supported_perf_cap = perf_cap; } static __init void vmx_set_cpu_caps(void) @@ -7946,7 +7947,7 @@ static __init void vmx_set_cpu_caps(void) if (!enable_pmu) kvm_cpu_cap_clear(X86_FEATURE_PDCM); - kvm_caps.supported_perf_cap = vmx_get_perf_capabilities(); + vmx_get_perf_capabilities(); if (!enable_sgx) { kvm_cpu_cap_clear(X86_FEATURE_SGX); diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index 38b73e98eae9..a29eb0469d7e 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -28,6 +28,7 @@ struct kvm_caps { u64 supported_mce_cap; u64 supported_xcr0; u64 supported_xss; + u64 host_perf_cap; u64 supported_perf_cap; };