KVM: x86: Check for pending interrupts when APICv is getting disabled

When APICv is active, interrupt injection doesn't raise KVM_REQ_EVENT
request (see __apic_accept_irq()) as the required work is done by hardware.
In case KVM_REQ_APICV_UPDATE collides with such injection, the interrupt
may never get delivered.

Currently, the described situation is hardly possible: all
kvm_request_apicv_update() calls normally happen upon VM creation when
no interrupts are pending. We are, however, going to move unconditional
kvm_request_apicv_update() call from kvm_hv_activate_synic() to
synic_update_vector() and without this fix 'hyperv_connections' test from
kvm-unit-tests gets stuck on IPI delivery attempt right after configuring
a SynIC route which triggers APICv disablement.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210609150911.1471882c-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -9137,6 +9137,15 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 	vcpu->arch.apicv_active = kvm_apicv_activated(vcpu->kvm);
 	kvm_apic_update_apicv(vcpu);
 	static_call(kvm_x86_refresh_apicv_exec_ctrl)(vcpu);
+
+	/*
+	 * When APICv gets disabled, we may still have injected interrupts
+	 * pending. At the same time, KVM_REQ_EVENT may not be set as APICv was
+	 * still active when the interrupt got accepted. Make sure
+	 * inject_pending_event() is called to check for that.
+	 */
+	if (!vcpu->arch.apicv_active)
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);