[PATCH 2/2] KVM: nVMX: avoid losing the posted notification interrupt when exiting L2

[Maxim Levitsky <mlevitsk@redhat.com>]

While delivering a nested posted interrupt notification
(see vmx_deliver_nested_posted_interrupt), KVM assumes that,
as long as the target vCPU is in the guest mode, KVM can send the
special POSTED_INTR_NESTED_VECTOR, which will either trigger APICv ucode
to inject all interrupts into L2 or cause a VM exit, after which
vmx_complete_nested_posted_interrupt is supposed to finish the job.

However, a third case is possible: if the target vCPU is about to exit
to L1, the posted notification interrupt must be instead injected
to L1' APIC, but KVM doesn't do this.

Detect this case in the nested VM exit path and act accordingly.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 2142e25c9b6c..4d8bb7f7fcd4 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2445,7 +2445,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
 			 ~PIN_BASED_VMX_PREEMPTION_TIMER);
 
 	/* Posted interrupts setting is only taken from vmcs12.  */
-	vmx->nested.pi_pending = false;
+	WARN_ON_ONCE(vmx->nested.pi_pending);
 	if (nested_cpu_has_posted_intr(vmcs12)) {
 		vmx->nested.posted_intr_nv = vmcs12->posted_intr_nv;
 	} else {
@@ -5162,6 +5162,14 @@ void __nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
 	kvm_clear_exception_queue(vcpu);
 	kvm_clear_interrupt_queue(vcpu);
 
+	if (lapic_in_kernel(vcpu) && vmx->nested.pi_pending) {
+		vmx->nested.pi_pending = 0;
+		if (!WARN_ON_ONCE(vmx->nested.posted_intr_nv == -1)) {
+			kvm_lapic_set_irr(vmx->nested.posted_intr_nv, vcpu->arch.apic);
+			kvm_make_request(KVM_REQ_EVENT, vcpu);
+		}
+	}
+
 	vmx_switch_vmcs(vcpu, &vmx->vmcs01);
 
 	kvm_nested_vmexit_handle_ibrs(vcpu);
-- 
2.54.0