Re: [PATCH 3/3] KVM: x86: fix ready_for_interrupt reporting in split IRQ chip case

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/11/2015 20:07, Matt Gingell wrote:
> This patch adds a call to kvm_arch_interrupt_allowed to ensure ready for
> interrupt is reported to user space correctly. This addresses a problem
> observed in QEMU when kvm->ready_for_interrupt is set but the x86
> interrupt flag is clear.
> 
> Additionally, test that the APIC is ready to accept an interrupt before
> reporting we are ready for injection.
> 
> Reviewed-by: Andy Honig <ahonig@google.com>
> Signed-off-by: Matt Gingell <gingell@google.com>

I think you need to add the same call to dm_request_for_irq_injection, like

-	return (irqchip_split(vcpu->kvm)
-		? kvm_apic_accept_pic_intr(vcpu)
-		: kvm_arch_interrupt_allowed(vcpu));
+	if (!kvm_arch_interrupt_allowed(vcpu))
+		return false;
+
+	return !lapic_in_kernel(vcpu) || kvm_apic_accept_pic_intr(vcpu);

At this point, just to err on the safe side, we probably should test
kvm_event_needs_reinjection(vcpu) as well in dm_request_for_irq_injection.

We can then make a new function kvm_vcpu_ready_for_interrupt_injection
with the sequence of tests (kvm_cpu_has_interrupt,
kvm_arch_interrupt_allowed, kvm_event_needs_reinjection, possibly
kvm_apic_accept_pic_intr) so that:

- dm_request_for_irq_injection becomes simply

	return (vcpu->run->request_interrupt_window &&
		likely(!pic_in_kernel(vcpu->kvm));

- the caller of dm_request_for_irq_injection does

	if (dm_request_for_irq_injection(vcpu) &&
	    kvm_vcpu_ready_for_interrupt_injection(vcpu))

- post_kvm_run_save's assignment becomes

	kvm_run->ready_for_interrupt_injection =
		!pic_in_kernel(vcpu->kvm) ||
		kvm_vcpu_ready_for_interrupt_injection(vcpu);

The code would make a lot of sense then; I hope it will work too. :)

Paolo "ceci n'est pas une patch"