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>

1 files changed, 11 insertions, 6 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a84ac7b570e6..5b8394a3a6b2 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -414,9 +414,17 @@ void __init alternative_instructions(void)
            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 @@ void __init alternative_instructions(void)
                                 (unsigned long)__smp_locks_end);
 
         restart_nmi();
-#ifdef CONFIG_X86_MCE
-        restart_mce();
-#endif
 }
 
 /**