qubes-linux-kernel/0003-mce-hide-EBUSY-initialization-error-on-Xen.patch

From 2d71f4d315dfcaaa9e4c1e3693e391f9d2b0a8b4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
 <marmarek@invisiblethingslab.com>
Date: Tue, 5 Jan 2016 02:44:04 +0100
Subject: [PATCH] mce: hide EBUSY initialization error on Xen
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In case of Xen, the device is already registered by xen mcelog (in
xen_late_init_mcelog), so fail here is expected. Note that
mcheck_init_device call is still expected to initialize mce_device. Comment
from threshold_init_device explaining the situation:

/*
 * there are 3 funcs which need to be _initcalled in a logic sequence:
 * 1. xen_late_init_mcelog
 * 2. mcheck_init_device
 * 3. threshold_init_device
 *
 * xen_late_init_mcelog must register xen_mce_chrdev_device before
 * native mce_chrdev_device registration if running under xen platform;
 *
 * mcheck_init_device should be inited before threshold_init_device to
 * initialize mce_device, otherwise a NULL ptr dereference will cause panic.
 *
 * so we use following _initcalls
 * 1. device_initcall(xen_late_init_mcelog);
 * 2. device_initcall_sync(mcheck_init_device);
 * 3. late_initcall(threshold_init_device);
 *
 * when running under xen, the initcall order is 1,2,3;
 * on baremetal, we skip 1 and we do only 2 and 3.
 */

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 953b3ce92dcc..e0bb9b52d8d1 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -52,6 +52,10 @@
 #include <asm/msr.h>
 #include <asm/reboot.h>
 
+#ifdef CONFIG_XEN_MCE_LOG
+#include <xen/xen.h>
+#endif
+
 #include "mce-internal.h"
 
 static DEFINE_MUTEX(mce_log_mutex);
@@ -2395,6 +2399,11 @@ static __init int mcheck_init_device(void)
 	free_cpumask_var(mce_device_initialized);
 
 err_out:
+#ifdef CONFIG_XEN_MCE_LOG
+	/* in case of Xen, the character device was already registered, so do not
+	 * treat this as an error */
+	if (!xen_initial_domain() || err != -EBUSY)
+#endif
 	pr_err("Unable to init MCE device (rc: %d)\n", err);
 
 	return err;
-- 
2.17.1