Messages in this thread | | | From | "Huang, Kai" <> | Subject | Re: [PATCH v3 07/15] KVM: nVMX: Use KVM-governed feature framework to track "nested VMX enabled" | Date | Wed, 16 Aug 2023 02:45:38 +0000 |
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On Tue, 2023-08-15 at 13:36 -0700, Sean Christopherson wrote: > Track "VMX exposed to L1" via a governed feature flag instead of using a > dedicated helper to provide the same functionality. The main goal is to > drive convergence between VMX and SVM with respect to querying features > that are controllable via module param (SVM likes to cache nested > features), avoiding the guest CPUID lookups at runtime is just a bonus > and unlikely to provide any meaningful performance benefits. > > No functional change intended. > > [...]
> > -/* > - * nested_vmx_allowed() checks whether a guest should be allowed to use VMX > - * instructions and MSRs (i.e., nested VMX). Nested VMX is disabled for > - * all guests if the "nested" module option is off, and can also be disabled > - * for a single guest by disabling its VMX cpuid bit. > - */ > -bool nested_vmx_allowed(struct kvm_vcpu *vcpu) > -{ > - return nested && guest_cpuid_has(vcpu, X86_FEATURE_VMX); > -} > - >
[...]
> @@ -7750,13 +7739,15 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) > guest_cpuid_has(vcpu, X86_FEATURE_XSAVE)) > kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_XSAVES); > > + kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_VMX); > + >
Nit:
nested_vmx_allowed() also checks 'nested' global variable. However kvm_governed_feature_check_and_set() is called unconditionally. Although IIUC it should never actually set the VMX governed bit when 'nested=0', it's not that obvious in _this_ patch.
Should we explicitly call this out in the changelog so git blamers can understand this more easily in the future?
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