linux-kernel - [patch] disable NMI watchdog by default

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Message-ID: <20070114092926.GA14465@elte.hu>
Date:	Sun, 14 Jan 2007 10:29:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>, Linus Torvalds <torvalds@...l.org>
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org
Subject: [patch] disable NMI watchdog by default

From: Ingo Molnar <mingo@...e.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@...e.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
-
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