On Fri, Aug 27, 2021, Peter Zijlstra wrote:
> On Thu, Aug 26, 2021 at 05:57:10PM -0700, Sean Christopherson wrote:
> > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> > index 5cedc0e8a5d5..4c5ba4128b38 100644
> > --- a/arch/x86/kvm/x86.h
> > +++ b/arch/x86/kvm/x86.h
> > @@ -395,9 +395,10 @@ static inline void kvm_unregister_perf_callbacks(void)
> >
> > DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu);
> >
> > -static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu)
> > +static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu, bool is_nmi)
> > {
> > __this_cpu_write(current_vcpu, vcpu);
> > + WRITE_ONCE(vcpu->arch.handling_nmi_from_guest, is_nmi);
> >
> > kvm_register_perf_callbacks();
> > }
> > @@ -406,6 +407,7 @@ static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
> > {
> > kvm_unregister_perf_callbacks();
> >
> > + WRITE_ONCE(vcpu->arch.handling_nmi_from_guest, false);
> > __this_cpu_write(current_vcpu, NULL);
> > }
>
> Does this rely on kvm_{,un}register_perf_callback() being a function
> call and thus implying a sequence point to order the stores?
No, I'm just terrible at remembering which macros provide what ordering guarantees,
i.e. I was thinking WRITE_ONCE provided guarantees against compiler reordering.
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