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/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c
index 4d8450ee3635..a66d607f5b92 100644
--- a/arch/x86_64/kernel/mce.c
+++ b/arch/x86_64/kernel/mce.c
@@ -667,6 +667,20 @@ static struct miscdevice mce_log_device = {
         &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. 
  */