Re: [PATCH 07/15] KVM: Use dedicated flag to track if KVM is handling an NMI from guest

[Peter Zijlstra]

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?