[PATCH] x86/MCE, xen/mcelog: Make /dev/mcelog registration messages more precise

[Borislav Petkov]

From: Juergen Gross <jgross@xxxxxxxx>

When running under Xen as dom0, /dev/mcelog is being provided by Xen
instead of the normal mcelog character device of the MCE core. Convert
an error message being issued by the MCE core in this case to an
informative message that Xen has registered the device.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: linux-edac <linux-edac@xxxxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20170614084059.19294-1-jgross@xxxxxxxx
[ Massage a bit. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/kernel/cpu/mcheck/dev-mcelog.c | 8 +++++++-
 drivers/xen/mcelog.c                    | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
index a80427c30c93..10cec43aac38 100644
--- a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
+++ b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
@@ -415,9 +415,15 @@ static __init int dev_mcelog_init_device(void)
 	/* register character device /dev/mcelog */
 	err = misc_register(&mce_chrdev_device);
 	if (err) {
-		pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
+		if (err == -EBUSY)
+			/* Xen dom0 might have registered the device already. */
+			pr_info("Unable to init device /dev/mcelog, already registered");
+		else
+			pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
+
 		return err;
 	}
+
 	mce_register_decode_chain(&dev_mcelog_nb);
 	return 0;
 }
diff --git a/drivers/xen/mcelog.c b/drivers/xen/mcelog.c
index a493c7315e94..6cc1c15bcd84 100644
--- a/drivers/xen/mcelog.c
+++ b/drivers/xen/mcelog.c
@@ -408,6 +408,8 @@ static int __init xen_late_init_mcelog(void)
 	if (ret)
 		goto deregister;
 
+	pr_info("/dev/mcelog registered by Xen\n");
+
 	return 0;
 
 deregister:
-- 
2.13.0