Xen can support console_io hypercalls for any domains, not just dom0,
depending on DEBUG and XSM policies. These hypercalls can be very useful
for development and debugging.

Introduce a kernel command line option xen_console_io to enable the
usage of console_io hypercalls for any domain upon request. When
xen_console_io is not specified, the current behavior is retained.

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
---
 .../admin-guide/kernel-parameters.txt         |  5 +++
 drivers/tty/hvc/hvc_xen.c                     | 33 ++++++++++++++++---
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e88505e945d52..953d3f597f007 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7620,6 +7620,11 @@
 			save/restore/migration must be enabled to handle larger
 			domains.
 
+	xen_console_io	[XEN,EARLY]
+			Boolean option to enable/disable the usage of the Xen
+			console_io hypercalls to read and write to the console.
+			Mostly useful for debugging and development.
+
 	xen_emul_unplug=		[HW,X86,XEN,EARLY]
 			Unplug Xen emulated devices
 			Format: [unplug0,][unplug1]
diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index 388a71afd6efe..299b08c90bab1 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -51,6 +51,28 @@ static DEFINE_SPINLOCK(xencons_lock);
 
 /* ------------------------------------------------------------------ */
 
+static bool xen_console_io = false;
+static int __initdata opt_console_io = -1;
+
+static int __init parse_xen_console_io(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (strcmp(arg, "off") == 0 ||
+	    strcmp(arg, "disabled") == 0 ||
+	    strcmp(arg, "0") == 0) {
+		opt_console_io = 0;
+	}
+	else if (strcmp(arg, "on") == 0 ||
+		 strcmp(arg, "enabled") == 0 ||
+		 strcmp(arg, "1") == 0) {
+		opt_console_io = 1;
+	}
+	return 0;
+}
+early_param("xen_console_io", parse_xen_console_io);
+
 static struct xencons_info *vtermno_to_xencons(int vtermno)
 {
 	struct xencons_info *entry, *ret = NULL;
@@ -331,7 +353,7 @@ static int xen_initial_domain_console_init(void)
 	struct xencons_info *info;
 	unsigned long flags;
 
-	if (!xen_initial_domain())
+	if (!xen_console_io)
 		return -ENODEV;
 
 	info = vtermno_to_xencons(HVC_COOKIE);
@@ -369,7 +391,7 @@ void xen_console_resume(void)
 {
 	struct xencons_info *info = vtermno_to_xencons(HVC_COOKIE);
 	if (info != NULL && info->irq) {
-		if (!xen_initial_domain())
+		if (!xen_console_io)
 			xen_console_update_evtchn(info);
 		rebind_evtchn_irq(info->evtchn, info->irq);
 	}
@@ -601,7 +623,7 @@ static int __init xen_hvc_init(void)
 	if (!xen_domain())
 		return -ENODEV;
 
-	if (xen_initial_domain()) {
+	if (xen_console_io) {
 		ops = &dom0_hvc_ops;
 		r = xen_initial_domain_console_init();
 		if (r < 0)
@@ -651,10 +673,13 @@ static int xen_cons_init(void)
 {
 	const struct hv_ops *ops;
 
+	xen_console_io = opt_console_io >= 0 ? opt_console_io :
+					       xen_initial_domain();
+
 	if (!xen_domain())
 		return 0;
 
-	if (xen_initial_domain())
+	if (xen_console_io)
 		ops = &dom0_hvc_ops;
 	else {
 		int r;
-- 
2.25.1

On 10.01.26 00:18, Stefano Stabellini wrote:
> Xen can support console_io hypercalls for any domains, not just dom0,
> depending on DEBUG and XSM policies. These hypercalls can be very useful
> for development and debugging.
> 
> Introduce a kernel command line option xen_console_io to enable the
> usage of console_io hypercalls for any domain upon request. When
> xen_console_io is not specified, the current behavior is retained.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
> ---
>   .../admin-guide/kernel-parameters.txt         |  5 +++
>   drivers/tty/hvc/hvc_xen.c                     | 33 ++++++++++++++++---
>   2 files changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index e88505e945d52..953d3f597f007 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7620,6 +7620,11 @@
>   			save/restore/migration must be enabled to handle larger
>   			domains.
>   
> +	xen_console_io	[XEN,EARLY]
> +			Boolean option to enable/disable the usage of the Xen
> +			console_io hypercalls to read and write to the console.
> +			Mostly useful for debugging and development.
> +
>   	xen_emul_unplug=		[HW,X86,XEN,EARLY]
>   			Unplug Xen emulated devices
>   			Format: [unplug0,][unplug1]
> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> index 388a71afd6efe..299b08c90bab1 100644
> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -51,6 +51,28 @@ static DEFINE_SPINLOCK(xencons_lock);
>   
>   /* ------------------------------------------------------------------ */
>   
> +static bool xen_console_io = false;
> +static int __initdata opt_console_io = -1;
> +
> +static int __init parse_xen_console_io(char *arg)
> +{
> +	if (!arg)
> +		return -EINVAL;
> +
> +	if (strcmp(arg, "off") == 0 ||
> +	    strcmp(arg, "disabled") == 0 ||
> +	    strcmp(arg, "0") == 0) {
> +		opt_console_io = 0;
> +	}
> +	else if (strcmp(arg, "on") == 0 ||
> +		 strcmp(arg, "enabled") == 0 ||
> +		 strcmp(arg, "1") == 0) {
> +		opt_console_io = 1;
> +	}

I'd prefer use of kstrtobool() instead of open-coding something similar.


Juergen