1 files changed, 23 insertions, 23 deletions

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index d3d91dae065..1e456dca4f6 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -209,29 +209,28 @@ static int xen_hvm_console_init(void)
 		info = kzalloc(sizeof(struct xencons_info), GFP_KERNEL | __GFP_ZERO);
 		if (!info)
 			return -ENOMEM;
-	}
-
-	/* already configured */
-	if (info->intf != NULL)
+	} else if (info->intf != NULL) {
+		/* already configured */
 		return 0;
-
-	r = hvm_get_parameter(HVM_PARAM_CONSOLE_EVTCHN, &v);
-	if (r < 0) {
-		kfree(info);
-		return -ENODEV;
 	}
+	/*
+	 * If the toolstack (or the hypervisor) hasn't set these values, the
+	 * default value is 0. Even though mfn = 0 and evtchn = 0 are
+	 * theoretically correct values, in practice they never are and they
+	 * mean that a legacy toolstack hasn't initialized the pv console correctly.
+	 */
+	r = hvm_get_parameter(HVM_PARAM_CONSOLE_EVTCHN, &v);
+	if (r < 0 || v == 0)
+		goto err;
 	info->evtchn = v;
-	hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &v);
-	if (r < 0) {
-		kfree(info);
-		return -ENODEV;
-	}
+	v = 0;
+	r = hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &v);
+	if (r < 0 || v == 0)
+		goto err;
 	mfn = v;
 	info->intf = ioremap(mfn << PAGE_SHIFT, PAGE_SIZE);
-	if (info->intf == NULL) {
-		kfree(info);
-		return -ENODEV;
-	}
+	if (info->intf == NULL)
+		goto err;
 	info->vtermno = HVC_COOKIE;
 
 	spin_lock(&xencons_lock);
@@ -239,6 +238,9 @@ static int xen_hvm_console_init(void)
 	spin_unlock(&xencons_lock);
 
 	return 0;
+err:
+	kfree(info);
+	return -ENODEV;
 }
 
 static int xen_pv_console_init(void)
@@ -256,12 +258,10 @@ static int xen_pv_console_init(void)
 		info = kzalloc(sizeof(struct xencons_info), GFP_KERNEL | __GFP_ZERO);
 		if (!info)
 			return -ENOMEM;
-	}
-
-	/* already configured */
-	if (info->intf != NULL)
+	} else if (info->intf != NULL) {
+		/* already configured */
 		return 0;
-
+	}
 	info->evtchn = xen_start_info->console.domU.evtchn;
 	info->intf = mfn_to_virt(xen_start_info->console.domU.mfn);
 	info->vtermno = HVC_COOKIE;