Messages in this thread | | | Date | Fri, 17 Nov 2023 16:33:27 +0800 | Subject | Re: [PATCH 3/9] KVM: x86: Initialize guest cpu_caps based on guest CPUID | From | "Yang, Weijiang" <> |
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On 11/17/2023 6:29 AM, Sean Christopherson wrote: > On Thu, Nov 16, 2023, Weijiang Yang wrote: >> On 11/11/2023 7:55 AM, Sean Christopherson wrote: >> >> [...] >> >>> -static __always_inline void guest_cpu_cap_check_and_set(struct kvm_vcpu *vcpu, >>> - unsigned int x86_feature) >>> +static __always_inline void guest_cpu_cap_clear(struct kvm_vcpu *vcpu, >>> + unsigned int x86_feature) >>> { >>> - if (kvm_cpu_cap_has(x86_feature) && guest_cpuid_has(vcpu, x86_feature)) >>> + unsigned int x86_leaf = __feature_leaf(x86_feature); >>> + >>> + reverse_cpuid_check(x86_leaf); >>> + vcpu->arch.cpu_caps[x86_leaf] &= ~__feature_bit(x86_feature); >>> +} >>> + >>> +static __always_inline void guest_cpu_cap_change(struct kvm_vcpu *vcpu, >>> + unsigned int x86_feature, >>> + bool guest_has_cap) >>> +{ >>> + if (guest_has_cap) >>> guest_cpu_cap_set(vcpu, x86_feature); >>> + else >>> + guest_cpu_cap_clear(vcpu, x86_feature); >>> +} >> I don't see any necessity to add 3 functions, i.e., guest_cpu_cap_{set, clear, change}, for > I want to have equivalents to the cpuid_entry_*() APIs so that we don't end up > with two different sets of names. And the clear() API already has a second user. > >> guest_cpu_cap update. IMHO one function is enough, e.g,: > Hrm, I open coded the OR/AND logic in cpuid_entry_change() to try to force CMOV > instead of Jcc. That honestly seems like a pointless optimization. I would > rather use the helpers, which is less code. > >> static __always_inline void guest_cpu_cap_update(struct kvm_vcpu *vcpu, >> unsigned int x86_feature, >> bool guest_has_cap) >> { >> unsigned int x86_leaf = __feature_leaf(x86_feature); >> >> reverse_cpuid_check(x86_leaf); >> if (guest_has_cap) >> vcpu->arch.cpu_caps[x86_leaf] |= __feature_bit(x86_feature); >> else >> vcpu->arch.cpu_caps[x86_leaf] &= ~__feature_bit(x86_feature); >> } >> >>> + >>> +static __always_inline void guest_cpu_cap_restrict(struct kvm_vcpu *vcpu, >>> + unsigned int x86_feature) >>> +{ >>> + if (!kvm_cpu_cap_has(x86_feature)) >>> + guest_cpu_cap_clear(vcpu, x86_feature); >>> } >> _restrict is not clear to me for what the function actually does -- it >> conditionally clears guest cap depending on KVM support of the feature. >> >> How about renaming it to guest_cpu_cap_sync()? > "sync" isn't correct because it's not synchronizing with KVM's capabilitiy, e.g. > the guest capability will remaing unset if the guest CPUID bit is clear but the > KVM capability is available. > > How about constrain()? I don't know, just feel we already have guest_cpu_cap_{set, clear, change}, here the name cannot exactly match the behavior of the function, maybe guest_cpu_cap_filter()? But just ignore the nit, up to you to decide the name :-)
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