Re: [PATCH v3] KVM: x86: Inject pending interrupt even if pending nmi exist

[Paolo Bonzini <pbonzini@redhat.com>]

On 24/03/2016 06:17, Yuki Shibuya wrote:
> Non maskable interrupts (NMI) are preferred to interrupts in current
> implementation. If a NMI is pending and NMI is blocked by the result
> of nmi_allowed(), pending interrupt is not injected and
> enable_irq_window() is not executed, even if interrupts injection is
> allowed.
> 
> In old kernel (e.g. 2.6.32), schedule() is often called in NMI context.
> In this case, interrupts are needed to execute iret that intends end
> of NMI. The flag of blocking new NMI is not cleared until the guest
> execute the iret, and interrupts are blocked by pending NMI. Due to
> this, iret can't be invoked in the guest, and the guest is starved
> until block is cleared by some events (e.g. canceling injection).
> 
> This patch injects pending interrupts, when it's allowed, even if NMI
> is blocked. And, If an interrupts is pending after executing
> inject_pending_event(), enable_irq_window() is executed regardless of
> NMI pending counter.
> 
> Signed-off-by: Yuki Shibuya <shibuya.yk@ncos.nec.co.jp>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/x86.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7236bd3..d4fd555 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6087,12 +6087,10 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>  	}
>  
>  	/* try to inject new event if pending */
> -	if (vcpu->arch.nmi_pending) {
> -		if (kvm_x86_ops->nmi_allowed(vcpu)) {
> -			--vcpu->arch.nmi_pending;
> -			vcpu->arch.nmi_injected = true;
> -			kvm_x86_ops->set_nmi(vcpu);
> -		}
> +	if (vcpu->arch.nmi_pending && kvm_x86_ops->nmi_allowed(vcpu)) {
> +		--vcpu->arch.nmi_pending;
> +		vcpu->arch.nmi_injected = true;
> +		kvm_x86_ops->set_nmi(vcpu);
>  	} else if (kvm_cpu_has_injectable_intr(vcpu)) {
>  		/*
>  		 * Because interrupts can be injected asynchronously, we are
> @@ -6561,10 +6559,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  		if (inject_pending_event(vcpu, req_int_win) != 0)
>  			req_immediate_exit = true;
>  		/* enable NMI/IRQ window open exits if needed */
> -		else if (vcpu->arch.nmi_pending)
> -			kvm_x86_ops->enable_nmi_window(vcpu);
> -		else if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
> -			kvm_x86_ops->enable_irq_window(vcpu);
> +		else {
> +			if (vcpu->arch.nmi_pending)
> +				kvm_x86_ops->enable_nmi_window(vcpu);
> +			if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
> +				kvm_x86_ops->enable_irq_window(vcpu);
> +		}
>  
>  		if (kvm_lapic_enabled(vcpu)) {
>  			update_cr8_intercept(vcpu);
> 

Thanks, queued for 4.6 and stable.

Paolo