x86: Stop MCEs and NMIs during code patching

When a machine check or NMI occurs while multiple byte code is patched
the CPU could theoretically see an inconsistent instruction and crash.
Prevent this by temporarily disabling MCEs and returning early in the
NMI handler.

Based on discussion with Mathieu Desnoyers.

Cc: Mathieu Desnoyers <compudj@krystal.dyndns.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/arch/i386/kernel/cpu/mcheck/mce.c b/arch/i386/kernel/cpu/mcheck/mce.c
index 56cd485b127c..34c781eddee4 100644
--- a/arch/i386/kernel/cpu/mcheck/mce.c
+++ b/arch/i386/kernel/cpu/mcheck/mce.c
@@ -60,6 +60,20 @@ void mcheck_init(struct cpuinfo_x86 *c)
         }
 }
 
+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;