Messages in this thread | | | Date | Wed, 16 Aug 2023 15:08:53 +0800 | Subject | Re: [PATCH v10 3/9] KVM: x86: Use KVM-governed feature framework to track "LAM enabled" | From | Binbin Wu <> |
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On 8/16/2023 11:46 AM, Huang, Kai wrote: > On Wed, 2023-07-19 at 22:41 +0800, Binbin Wu wrote: >> Use the governed feature framework to track if Linear Address Masking (LAM) >> is "enabled", i.e. if LAM can be used by the guest. So that guest_can_use() >> can be used to support LAM virtualization. > Better to explain why to use governed feature for LAM? Is it because there's > hot path(s) calling guest_cpuid_has()? Anyway some context of why can help > here. Yes, to avoid calling guest_cpuid_has() in CR3 handling and instruction emulation paths. I will add the context next version. Thanks!
> >> LAM modifies the checking that is applied to 64-bit linear addresses, allowing >> software to use of the untranslated address bits for metadata and masks the >> metadata bits before using them as linear addresses to access memory. >> >> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com> >> --- >> arch/x86/kvm/governed_features.h | 2 ++ >> arch/x86/kvm/vmx/vmx.c | 3 +++ >> 2 files changed, 5 insertions(+) >> >> diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h >> index 40ce8e6608cd..708578d60e6f 100644 >> --- a/arch/x86/kvm/governed_features.h >> +++ b/arch/x86/kvm/governed_features.h >> @@ -5,5 +5,7 @@ BUILD_BUG() >> >> #define KVM_GOVERNED_X86_FEATURE(x) KVM_GOVERNED_FEATURE(X86_FEATURE_##x) >> >> +KVM_GOVERNED_X86_FEATURE(LAM) >> + >> #undef KVM_GOVERNED_X86_FEATURE >> #undef KVM_GOVERNED_FEATURE >> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >> index 0ecf4be2c6af..ae47303c88d7 100644 >> --- a/arch/x86/kvm/vmx/vmx.c >> +++ b/arch/x86/kvm/vmx/vmx.c >> @@ -7783,6 +7783,9 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) >> vmx->msr_ia32_feature_control_valid_bits &= >> ~FEAT_CTL_SGX_LC_ENABLED; >> >> + if (boot_cpu_has(X86_FEATURE_LAM)) >> + kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_LAM); >> + > If you want to use boot_cpu_has(), it's better to be done at your last patch to > only set the cap bit when boot_cpu_has() is true, I suppose. Yes, but new version of kvm_governed_feature_check_and_set() of KVM-governed feature framework will check against kvm_cpu_cap_has() as well. I will remove the if statement and call kvm_governed_feature_check_and_set() directly. https://lore.kernel.org/kvm/20230815203653.519297-2-seanjc@google.com/
> >> /* Refresh #PF interception to account for MAXPHYADDR changes. */ >> vmx_update_exception_bitmap(vcpu); >> }
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