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>
---
Changes in v3:
- mark xen_cons_init as __init

Changes in v2:
- use kstrtobool
---
 .../admin-guide/kernel-parameters.txt         |  5 ++++
 drivers/tty/hvc/hvc_xen.c                     | 29 +++++++++++++++----
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a8d0afde7f85a..68ab6fa72b685 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -8414,6 +8414,11 @@ Kernel parameters
 			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..95ec01b1aacf0 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -51,6 +51,22 @@ 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)
+{
+	bool val;
+	int ret;
+
+	ret = kstrtobool(arg, &val);
+	if (ret == 0)
+		opt_console_io = (int)val;
+
+	return ret;
+}
+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 +347,7 @@ 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 +385,7 @@ 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 +617,7 @@ 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)
@@ -647,14 +663,17 @@ static int __init xen_hvc_init(void)
 }
 device_initcall(xen_hvc_init);
 
-static int xen_cons_init(void)
+static int __init 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 14.01.26 00:24, 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>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen