kvm tools: don't exit on debug ioport write

While it shouldn't happen on regular guests, we sometimes hit it when fuzzing
within the guest, which would cause the lkvm process to exit - which is
undesired.

Our PIT tests were using the debug port to trigger a reboot. Instead of using
that port we now use the reboot line of our i8042 controller.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

tests/pit/tick.S

@@ -4,15 +4,6 @@
 #define TIMER_FREQ	1193182
 #define TIMER_DIV(x)	((TIMER_FREQ+(x)/2)/(x))
 
-/*
- * hpa noted:
- *
- * 0xe0..0xef are "motherboard specific", but 0xe9 is
- * used for Bochs debugging and 0xed is the Phoenix-reserved
- * delay port
- */
-#define DBG_PORT	0xe0
-
 #define TEST_COUNT	0x0200
 
 	.code16gcc
@@ -82,8 +73,9 @@ test_ok:
 	mov	$(msg2_end-msg2), %cx
 	cs rep/outsb
 
-	/* not a valid port to force exit */
-	outb	%al, $DBG_PORT
+	/* Reboot by using the i8042 reboot line */
+	mov	$0xfe, %al
+	outb	%al, $0x64
 
 timer_isr:
 	cli

x86/ioport.c

@@ -5,7 +5,7 @@
 
 static bool debug_io_out(struct ioport *ioport, struct kvm *kvm, u16 port, void *data, int size)
 {
-	exit(EXIT_SUCCESS);
+	return 0;
 }
 
 static struct ioport_operations debug_ops = {