.../admin-guide/kernel-parameters.txt | 5 ++++ drivers/tty/hvc/hvc_xen.c | 27 ++++++++++++++++--- 2 files changed, 28 insertions(+), 4 deletions(-)
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 v2:
- use kstrtobool
---
.../admin-guide/kernel-parameters.txt | 5 ++++
drivers/tty/hvc/hvc_xen.c | 27 ++++++++++++++++---
2 files changed, 28 insertions(+), 4 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..c94cc7df78d36 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)
@@ -651,10 +667,13 @@ 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;
--
2.25.1On 13.01.26 01:24, 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
On 13.01.26 08:57, Jürgen Groß wrote: > On 13.01.26 01:24, 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> Sorry, I need to revoke my R-b. I get: WARNING: modpost: vmlinux: section mismatch in reference: xen_cons_init+0x0 (section: .text) -> opt_console_io (section: .init.data) I think xen_cons_init() should be __init, too. Juergen
On Tue, 13 Jan 2026, Juergen Gross wrote: > On 13.01.26 08:57, Jürgen Groß wrote: > > On 13.01.26 01:24, 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> > > Sorry, I need to revoke my R-b. > > I get: > > WARNING: modpost: vmlinux: section mismatch in reference: xen_cons_init+0x0 > (section: .text) -> opt_console_io (section: .init.data) > > I think xen_cons_init() should be __init, too. Yes you are right, good catch. I am cross-compiling x86 on ARM and my environment is not warning me about it. I made the change.
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