KVM: nVMX: Drop a superfluous WARN on reflecting EXTERNAL_INTERRUPT

Drop the WARN in nested_vmx_reflect_vmexit() that fires if KVM attempts
to reflect an external interrupt.  The WARN is blatantly impossible to
hit now that nested_vmx_l0_wants_exit() is called from
nested_vmx_reflect_vmexit() unconditionally returns true for
EXTERNAL_INTERRUPT.
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200415175519.14230-7-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -5863,12 +5863,11 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason)
 		return false;
 
 	/*
-	 * At this point, the exit interruption info in exit_intr_info
-	 * is only valid for EXCEPTION_NMI exits.  For EXTERNAL_INTERRUPT
-	 * we need to query the in-kernel LAPIC.
+	 * vmcs.VM_EXIT_INTR_INFO is only valid for EXCEPTION_NMI exits.  For
+	 * EXTERNAL_INTERRUPT, the value for vmcs12->vm_exit_intr_info would
+	 * need to be synthesized by querying the in-kernel LAPIC, but external
+	 * interrupts are never reflected to L1 so it's a non-issue.
 	 */
-	WARN_ON(exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT);
-
 	if ((exit_intr_info &
 	     (INTR_INFO_VALID_MASK | INTR_INFO_DELIVER_CODE_MASK)) ==
 	    (INTR_INFO_VALID_MASK | INTR_INFO_DELIVER_CODE_MASK)) {