| Message ID | 20190325080650.19896-3-xiaoyao.li@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Switch MSR_MISC_FEATURES_ENABLES and one optimization | expand |
On Mon, Mar 25, 2019 at 04:06:50PM +0800, Xiaoyao Li wrote: > KVM needs to switch MSR_MISC_FEATURES_ENABLES between host and guest in > every pcpu/vcpu context switch. Since WRMSR is expensive, this patch tries > to save cycles by avoiding WRMSR MSR_MISC_FEATURES_ENABLES whenever possible. > > If host's value is zero, nothing needs to be done, since guest can use > kvm emulated cpuid faulting. > > If host's value is non-zero, it need not clear MSR_MISC_FEATURES_ENABLES > unconditionally. We can use hardware cpuid faulting if guest's > value is equal to host'value, thus avoid WRMSR > MSR_MISC_FEATURES_ENABLES. > > Since hardware cpuid faulting takes higher priority than CPUID vm exit, > it should be updated to hardware while guest wrmsr and hardware cpuid > faulting is used for guest. > > Signed-off-by: Xiaoyao Li <xiaoyao.li@linux.intel.com> > --- > arch/x86/include/asm/kvm_host.h | 2 ++ > arch/x86/kvm/vmx/vmx.c | 13 ++++++++++--- > arch/x86/kvm/x86.c | 15 ++++++++++++--- > 3 files changed, 24 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 2c53df4a5a2a..9bcb444b903d 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1343,6 +1343,8 @@ void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw); > void kvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l); > int kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr); > > +int kvm_supported_msr_misc_features_enables(struct kvm_vcpu *vcpu, u64 data); > + > int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr); > int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr); > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 65aa947947ba..73bb11f74b36 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -1035,10 +1035,10 @@ static void vmx_prepare_guest_misc_features_enables(struct vcpu_vmx *vmx) > { > u64 msrval = this_cpu_read(msr_misc_features_shadow); > > - if (!msrval) > + if (!msrval || msrval == vmx->vcpu.arch.msr_misc_features_enables) > return; > > - wrmsrl(MSR_MISC_FEATURES_ENABLES, 0ULL); > + wrmsrl(MSR_MISC_FEATURES_ENABLES, vmx->vcpu.arch.msr_misc_features_enables); > } > > void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > @@ -1136,7 +1136,7 @@ static void vmx_load_host_misc_features_enables(struct vcpu_vmx *vmx) > { > u64 msrval = this_cpu_read(msr_misc_features_shadow); > > - if (!msrval) > + if (!msrval || msrval == vmx->vcpu.arch.msr_misc_features_enables) > return; > > wrmsrl(MSR_MISC_FEATURES_ENABLES, msrval); > @@ -2043,6 +2043,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > else > vmx->pt_desc.guest.addr_a[index / 2] = data; > break; > + case MSR_MISC_FEATURES_ENABLES: > + if (!kvm_supported_msr_misc_features_enables(vcpu, data)) > + return 1; > + if (this_cpu_read(msr_misc_features_shadow) && vmx->loaded_cpu_state) > + wrmsrl(MSR_MISC_FEATURES_ENABLES, data); > + vcpu->arch.msr_misc_features_enables = data; > + break; > case MSR_TSC_AUX: > if (!msr_info->host_initiated && > !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP)) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index ad1df965574e..d2af90422a51 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2449,6 +2449,17 @@ static void record_steal_time(struct kvm_vcpu *vcpu) > &vcpu->arch.st.steal, sizeof(struct kvm_steal_time)); > } > > +int kvm_supported_msr_misc_features_enables(struct kvm_vcpu *vcpu, u64 data) The name kvm_supported_msr_misc_features_enables() is a bit confusing, e.g. I expected it to return a bitmask of the supported features. Maybe kvm_misc_features_enables_msr_valid() to be consistent with vmx_feature_control_msr_valid()? > +{ > + if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT || > + (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && > + !supports_cpuid_fault(vcpu))) > + return 0; > + else > + return 1; No need for the if-else, you can simply do: return (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT) || (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && !supports_cpuid_fault(vcpu)); You could even shorten it to: return (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT) || (data && !supports_cpuid_fault(vcpu)); although that might be getting a bit too cute. > +} > +EXPORT_SYMBOL_GPL(kvm_supported_msr_misc_features_enables); > + > int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > { > bool pr = false; > @@ -2669,9 +2680,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > vcpu->arch.msr_platform_info = data; > break; > case MSR_MISC_FEATURES_ENABLES: > - if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT || > - (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && > - !supports_cpuid_fault(vcpu))) > + if (!kvm_supported_msr_misc_features_enables(vcpu, data)) > return 1; > vcpu->arch.msr_misc_features_enables = data; > break; > -- > 2.19.1 >
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 2c53df4a5a2a..9bcb444b903d 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1343,6 +1343,8 @@ void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw); void kvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l); int kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr); +int kvm_supported_msr_misc_features_enables(struct kvm_vcpu *vcpu, u64 data); + int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr); int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr); diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 65aa947947ba..73bb11f74b36 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1035,10 +1035,10 @@ static void vmx_prepare_guest_misc_features_enables(struct vcpu_vmx *vmx) { u64 msrval = this_cpu_read(msr_misc_features_shadow); - if (!msrval) + if (!msrval || msrval == vmx->vcpu.arch.msr_misc_features_enables) return; - wrmsrl(MSR_MISC_FEATURES_ENABLES, 0ULL); + wrmsrl(MSR_MISC_FEATURES_ENABLES, vmx->vcpu.arch.msr_misc_features_enables); } void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) @@ -1136,7 +1136,7 @@ static void vmx_load_host_misc_features_enables(struct vcpu_vmx *vmx) { u64 msrval = this_cpu_read(msr_misc_features_shadow); - if (!msrval) + if (!msrval || msrval == vmx->vcpu.arch.msr_misc_features_enables) return; wrmsrl(MSR_MISC_FEATURES_ENABLES, msrval); @@ -2043,6 +2043,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) else vmx->pt_desc.guest.addr_a[index / 2] = data; break; + case MSR_MISC_FEATURES_ENABLES: + if (!kvm_supported_msr_misc_features_enables(vcpu, data)) + return 1; + if (this_cpu_read(msr_misc_features_shadow) && vmx->loaded_cpu_state) + wrmsrl(MSR_MISC_FEATURES_ENABLES, data); + vcpu->arch.msr_misc_features_enables = data; + break; case MSR_TSC_AUX: if (!msr_info->host_initiated && !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP)) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ad1df965574e..d2af90422a51 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2449,6 +2449,17 @@ static void record_steal_time(struct kvm_vcpu *vcpu) &vcpu->arch.st.steal, sizeof(struct kvm_steal_time)); } +int kvm_supported_msr_misc_features_enables(struct kvm_vcpu *vcpu, u64 data) +{ + if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT || + (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && + !supports_cpuid_fault(vcpu))) + return 0; + else + return 1; +} +EXPORT_SYMBOL_GPL(kvm_supported_msr_misc_features_enables); + int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) { bool pr = false; @@ -2669,9 +2680,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) vcpu->arch.msr_platform_info = data; break; case MSR_MISC_FEATURES_ENABLES: - if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT || - (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && - !supports_cpuid_fault(vcpu))) + if (!kvm_supported_msr_misc_features_enables(vcpu, data)) return 1; vcpu->arch.msr_misc_features_enables = data; break;
KVM needs to switch MSR_MISC_FEATURES_ENABLES between host and guest in every pcpu/vcpu context switch. Since WRMSR is expensive, this patch tries to save cycles by avoiding WRMSR MSR_MISC_FEATURES_ENABLES whenever possible. If host's value is zero, nothing needs to be done, since guest can use kvm emulated cpuid faulting. If host's value is non-zero, it need not clear MSR_MISC_FEATURES_ENABLES unconditionally. We can use hardware cpuid faulting if guest's value is equal to host'value, thus avoid WRMSR MSR_MISC_FEATURES_ENABLES. Since hardware cpuid faulting takes higher priority than CPUID vm exit, it should be updated to hardware while guest wrmsr and hardware cpuid faulting is used for guest. Signed-off-by: Xiaoyao Li <xiaoyao.li@linux.intel.com> --- arch/x86/include/asm/kvm_host.h | 2 ++ arch/x86/kvm/vmx/vmx.c | 13 ++++++++++--- arch/x86/kvm/x86.c | 15 ++++++++++++--- 3 files changed, 24 insertions(+), 6 deletions(-)