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

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Date:   Thu, 23 Apr 2020 17:35:25 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        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 Thu, 23 Apr 2020 at 17:25, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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.

We will not exit from vmx_vcpu_run to vcpu_enter_guest, so it will not
help, right?

    Wanpeng