KVM: nVMX: Re-evaluate L1 pending events when running L2 and L1 got posted-interrupt

In case posted-interrupt was delivered to CPU while it is in host
(outside guest), then posted-interrupt delivery will be done by
calling sync_pir_to_irr() at vmentry after interrupts are disabled.

sync_pir_to_irr() will check vmx->pi_desc.control ON bit and if
set, it will sync vmx->pi_desc.pir to IRR and afterwards update RVI to
ensure virtual-interrupt-delivery will dispatch interrupt to guest.

However, it is possible that L1 will receive a posted-interrupt while
CPU runs at host and is about to enter L2. In this case, the call to
sync_pir_to_irr() will indeed update the L1's APIC IRR but
vcpu_enter_guest() will then just resume into L2 guest without
re-evaluating if it should exit from L2 to L1 as a result of this
new pending L1 event.

To address this case, if sync_pir_to_irr() has a new L1 injectable
interrupt and CPU is running L2, we force exit GUEST_MODE which will
result in another iteration of vcpu_run() run loop which will call
kvm_vcpu_running() which will call check_nested_events() which will
handle the pending L1 event properly.
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/vmx.c

@@ -8978,6 +8978,7 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	int max_irr;
+	bool max_irr_updated;
 
 	WARN_ON(!vcpu->arch.apicv_active);
 	if (pi_test_on(&vmx->pi_desc)) {
@@ -8987,7 +8988,16 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
 		 * But on x86 this is just a compiler barrier anyway.
 		 */
 		smp_mb__after_atomic();
-		kvm_apic_update_irr(vcpu, vmx->pi_desc.pir, &max_irr);
+		max_irr_updated =
+			kvm_apic_update_irr(vcpu, vmx->pi_desc.pir, &max_irr);
+
+		/*
+		 * If we are running L2 and L1 has a new pending interrupt
+		 * which can be injected, we should re-evaluate
+		 * what should be done with this new L1 interrupt.
+		 */
+		if (is_guest_mode(vcpu) && max_irr_updated)
+			kvm_vcpu_exiting_guest_mode(vcpu);
 	} else {
 		max_irr = kvm_lapic_find_highest_irr(vcpu);
 	}