KVM: x86: Use kvm_queue_exception_e() to queue #DF

Queue #DF by recursing on kvm_multiple_exception() by way of
kvm_queue_exception_e() instead of open coding the behavior.  This will
allow KVM to Just Work when a future commit moves exception interception
checks (for L2 => L1) into kvm_multiple_exception().

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-17-seanjc@google.comSigned-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -667,25 +667,22 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
 	}
 	class1 = exception_class(prev_nr);
 	class2 = exception_class(nr);
-	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
-		|| (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
+	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY) ||
+	    (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
 		/*
-		 * Generate double fault per SDM Table 5-5.  Set
-		 * exception.pending = true so that the double fault
-		 * can trigger a nested vmexit.
+		 * Synthesize #DF.  Clear the previously injected or pending
+		 * exception so as not to incorrectly trigger shutdown.
 		 */
-		vcpu->arch.exception.pending = true;
 		vcpu->arch.exception.injected = false;
-		vcpu->arch.exception.has_error_code = true;
-		vcpu->arch.exception.vector = DF_VECTOR;
-		vcpu->arch.exception.error_code = 0;
-		vcpu->arch.exception.has_payload = false;
-		vcpu->arch.exception.payload = 0;
-	} else
+		vcpu->arch.exception.pending = false;
+
+		kvm_queue_exception_e(vcpu, DF_VECTOR, 0);
+	} else {
 		/* replace previous exception with a new one in a hope
 		   that instruction re-execution will regenerate lost
 		   exception */
 		goto queue;
+	}
 }
 
 void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)