On Fri, Nov 17, 2023 at 04:33:27PM +0800, Yang, Weijiang wrote:
> 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 :-)
How about guest_cpu_cap_kvm_restrict or guest_cpu_cap_kvm_constrain ?
>
>
