[patch] disable NMI watchdog by default

Ingo Molnar
2007-01-14T09:33:59Z

From: Ingo Molnar <mingo@elte.hu>
Subject: [patch] disable NMI watchdog by default

there's a new NMI watchdog related problem: KVM crashes on certain
bzImages because ... we enable the NMI watchdog by default (even if the
user does not ask for it) , and no other OS on this planet does that so
KVM doesnt have emulation for that yet. So KVM injects a #GP, which
crashes the Linux guest:

general protection fault: 0000 [#1]
PREEMPT SMP
Modules linked in:
CPU: 0
EIP: 0060:[<c011a8ae>] Not tainted VLI
EFLAGS: 00000246 (2.6.20-rc5-rt0 #3)
EIP is at setup_apic_nmi_watchdog+0x26d/0x3d3

and no, i did /not/ request an nmi_watchdog on the boot command line!

Solution: turn off that darn thing! It's a debug tool, not a 'make life
harder' tool!!

with this patch the KVM guest boots up just fine.

And with this my laptop (Lenovo T60) also stops its sporadic hard
hanging (sometimes in acpi_init(), sometimes later during bootup,
sometimes much later during actual use) as well. It hung with both
nmi_watchdog=1 and nmi_watchdog=2, so it's generally the fact of NMI
injection that is causing problems, not the NMI watchdog variant, nor
any particular bootup code.

The patch is unintrusive.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

Index: linux/include/asm-i386/nmi.h
===================================================================
--- linux.orig/include/asm-i386/nmi.h
+++ linux/include/asm-i386/nmi.h
@@ -33,7 +33,7 @@ extern int nmi_watchdog_tick (struct pt_

extern atomic_t nmi_active;
extern unsigned int nmi_watchdog;
-#define NMI_DEFAULT -1
+#define NMI_DEFAULT 0
#define NMI_NONE 0
#define NMI_IO_APIC 1
#define NMI_LOCAL_APIC 2
Index: linux/include/asm-x86_64/nmi.h
===================================================================
--- linux.orig/include/asm-x86_64/nmi.h
+++ linux/include/asm-x86_64/nmi.h
@@ -63,7 +63,7 @@ extern int setup_nmi_watchdog(char *);

extern atomic_t nmi_active;
extern unsigned int nmi_watchdog;
-#define NMI_DEFAULT -1
+#define NMI_DEFAULT 0
#define NMI_NONE 0
#define NMI_IO_APIC 1
#define NMI_LOCAL_APIC 2