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>

include/asm-i386/mce.h

@@ -5,3 +5,7 @@ extern void mcheck_init(struct cpuinfo_x86 *c);
 #endif
 
 extern int mce_disabled;
+
+extern void stop_mce(void);
+extern void restart_mce(void);
+

include/asm-i386/nmi.h

@@ -57,5 +57,7 @@ unsigned lapic_adjust_nmi_hz(unsigned hz);
 int lapic_watchdog_ok(void);
 void disable_lapic_nmi_watchdog(void);
 void enable_lapic_nmi_watchdog(void);
+void stop_nmi(void);
+void restart_nmi(void);
 
 #endif /* ASM_NMI_H */

include/asm-x86_64/mce.h

@@ -107,6 +107,9 @@ extern void do_machine_check(struct pt_regs *, long);
 
 extern int mce_notify_user(void);
 
+extern void stop_mce(void);
+extern void restart_mce(void);
+
 #endif
 
 #endif

include/asm-x86_64/nmi.h

@@ -88,5 +88,7 @@ unsigned lapic_adjust_nmi_hz(unsigned hz);
 int lapic_watchdog_ok(void);
 void disable_lapic_nmi_watchdog(void);
 void enable_lapic_nmi_watchdog(void);
+void stop_nmi(void);
+void restart_nmi(void);
 
 #endif /* ASM_NMI_H */