linux-kernel - Re: [PATCH v2 1/5] KVM: LAPIC: Introduce interrupt delivery fastpath

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Date:   Thu, 23 Apr 2020 11:25:00 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v2 1/5] KVM: LAPIC: Introduce interrupt delivery fastpath

On 23/04/20 11:01, Wanpeng Li wrote:
> +static void fast_deliver_interrupt(struct kvm_lapic *apic, int vector)
> +{
> +	struct kvm_vcpu *vcpu = apic->vcpu;
> +
> +	kvm_lapic_clear_vector(vector, apic->regs + APIC_TMR);
> +
> +	if (vcpu->arch.apicv_active) {
> +		if (kvm_x86_ops.pi_test_and_set_pir_on(vcpu, vector))
> +			return;
> +
> +		kvm_x86_ops.sync_pir_to_irr(vcpu);
> +	} else {
> +		kvm_lapic_set_irr(vector, apic);
> +		if (kvm_cpu_has_injectable_intr(vcpu)) {
> +			if (kvm_x86_ops.interrupt_allowed(vcpu)) {
> +				kvm_queue_interrupt(vcpu,
> +					kvm_cpu_get_interrupt(vcpu), false);
> +				kvm_x86_ops.set_irq(vcpu);
> +			} else
> +				kvm_x86_ops.enable_irq_window(vcpu);
> +		}
> +	}
> +}
> +

Ok, got it now.  The problem is that deliver_posted_interrupt goes through

        if (!kvm_vcpu_trigger_posted_interrupt(vcpu, false))
                kvm_vcpu_kick(vcpu);

Would it help to make the above

        if (vcpu != kvm_get_running_vcpu() &&
	    !kvm_vcpu_trigger_posted_interrupt(vcpu, false))
                kvm_vcpu_kick(vcpu);

?  If that is enough for the APICv case, it's good enough.

Paolo