commit 123aa76ec0cab5d4881cd8509faed43231e68801
author Andi Kleen <andi@firstfloor.org> Thu Feb 12 13:39:27 2009 +0100
committer H. Peter Anvin <hpa@linux.intel.com> Tue Feb 17 15:32:38 2009 -0800
tree 9b15b722f93adf886fc4dcbacea062325b2ea365
parent 973a2dd1d50a11d380086601f14e59116f93e8c5

x86, mce: don't disable machine checks during code patching

Impact: low priority bug fix

This removes part of a a patch I added myself some time ago. After some
consideration the patch was a bad idea. In particular it stopped machine check
exceptions during code patching.

To quote the comment:

        * MCEs only happen when something got corrupted and in this
        * case we must do something about the corruption.
        * Ignoring it is worse than a unlikely patching race.
        * Also machine checks tend to be broadcast and if one CPU
        * goes into machine check the others follow quickly, so we don't
        * expect a machine check to cause undue problems during to code
        * patching.

So undo the machine check related parts of
8f4e956b313dcccbc7be6f10808952345e3b638c NMIs are still disabled.

This only removes code, the only additions are a new comment.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/alternative.c

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a84ac7b..5b8394a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -414,9 +414,17 @@
 	   that might execute the to be patched code.
 	   Other CPUs are not running. */
 	stop_nmi();
-#ifdef CONFIG_X86_MCE
-	stop_mce();
-#endif
+
+	/*
+	 * Don't stop machine check exceptions while patching.
+	 * MCEs only happen when something got corrupted and in this
+	 * case we must do something about the corruption.
+	 * Ignoring it is worse than a unlikely patching race.
+	 * Also machine checks tend to be broadcast and if one CPU
+	 * goes into machine check the others follow quickly, so we don't
+	 * expect a machine check to cause undue problems during to code
+	 * patching.
+	 */
 
 	apply_alternatives(__alt_instructions, __alt_instructions_end);
 
@@ -456,9 +464,6 @@
 				(unsigned long)__smp_locks_end);
 
 	restart_nmi();
-#ifdef CONFIG_X86_MCE
-	restart_mce();
-#endif
 }
 
 /**

arch/x86/kernel/cpu/mcheck/mce_32.c

diff --git a/arch/x86/kernel/cpu/mcheck/mce_32.c b/arch/x86/kernel/cpu/mcheck/mce_32.c
index dfaebce..3552119 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_32.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_32.c
@@ -60,20 +60,6 @@
 	}
 }
 
-static unsigned long old_cr4 __initdata;
-
-void __init stop_mce(void)
-{
-	old_cr4 = read_cr4();
-	clear_in_cr4(X86_CR4_MCE);
-}
-
-void __init restart_mce(void)
-{
-	if (old_cr4 & X86_CR4_MCE)
-		set_in_cr4(X86_CR4_MCE);
-}
-
 static int __init mcheck_disable(char *str)
 {
 	mce_disabled = 1;

arch/x86/kernel/cpu/mcheck/mce_64.c

diff --git a/arch/x86/kernel/cpu/mcheck/mce_64.c b/arch/x86/kernel/cpu/mcheck/mce_64.c
index 5ed8099..25ccdbe 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_64.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_64.c
@@ -680,20 +680,6 @@
 	&mce_chrdev_ops,
 };
 
-static unsigned long old_cr4 __initdata;
-
-void __init stop_mce(void)
-{
-	old_cr4 = read_cr4();
-	clear_in_cr4(X86_CR4_MCE);
-}
-
-void __init restart_mce(void)
-{
-	if (old_cr4 & X86_CR4_MCE)
-		set_in_cr4(X86_CR4_MCE);
-}
-
 /*
  * Old style boot options parsing. Only for compatibility.
  */