KVM: nVMX: Fix loss of pending IRQ/NMI before entering L2

Consider the case L1 had a IRQ/NMI event until it executed
VMLAUNCH/VMRESUME which wasn't delivered because it was disallowed
(e.g. interrupts disabled). When L1 executes VMLAUNCH/VMRESUME,
L0 needs to evaluate if this pending event should cause an exit from
L2 to L1 or delivered directly to L2 (e.g. In case L1 don't intercept
EXTERNAL_INTERRUPT).

Usually this would be handled by L0 requesting a IRQ/NMI window
by setting VMCS accordingly. However, this setting was done on
VMCS01 and now VMCS02 is active instead. Thus, when L1 executes
VMLAUNCH/VMRESUME we force L0 to perform pending event evaluation by
requesting a KVM_REQ_EVENT.

Note that above scenario exists when L1 KVM is about to enter L2 but
requests an "immediate-exit". As in this case, L1 will
disable-interrupts and then send a self-IPI before entering L2.

Reviewed-by: Nikita Leshchenko <nikita.leshchenko@oracle.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/vmx.c

@@ -12537,8 +12537,11 @@ static int enter_vmx_non_root_mode(struct kvm_vcpu *vcpu, u32 *exit_qual)
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	bool from_vmentry = !!exit_qual;
 	u32 dummy_exit_qual;
+	u32 vmcs01_cpu_exec_ctrl;
 	int r = 0;
 
+	vmcs01_cpu_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
+
 	enter_guest_mode(vcpu);
 
 	if (!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS))
@@ -12574,6 +12577,25 @@ static int enter_vmx_non_root_mode(struct kvm_vcpu *vcpu, u32 *exit_qual)
 		kvm_make_request(KVM_REQ_GET_VMCS12_PAGES, vcpu);
 	}
 
+	/*
+	 * If L1 had a pending IRQ/NMI until it executed
+	 * VMLAUNCH/VMRESUME which wasn't delivered because it was
+	 * disallowed (e.g. interrupts disabled), L0 needs to
+	 * evaluate if this pending event should cause an exit from L2
+	 * to L1 or delivered directly to L2 (e.g. In case L1 don't
+	 * intercept EXTERNAL_INTERRUPT).
+	 *
+	 * Usually this would be handled by L0 requesting a
+	 * IRQ/NMI window by setting VMCS accordingly. However,
+	 * this setting was done on VMCS01 and now VMCS02 is active
+	 * instead. Thus, we force L0 to perform pending event
+	 * evaluation by requesting a KVM_REQ_EVENT.
+	 */
+	if (vmcs01_cpu_exec_ctrl &
+		(CPU_BASED_VIRTUAL_INTR_PENDING | CPU_BASED_VIRTUAL_NMI_PENDING)) {
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
+	}
+
 	/*
 	 * Note no nested_vmx_succeed or nested_vmx_fail here. At this point
 	 * we are no longer running L1, and VMLAUNCH/VMRESUME has not yet