arch/i386/kernel/nmi.c

/*
 *  linux/arch/i386/nmi.c
 *
 *  NMI watchdog support on APIC systems
 *
 *  Started by Ingo Molnar <mingo@redhat.com>
 *
 *  Fixes:
 *  Mikael Pettersson	: AMD K7 support for local APIC NMI watchdog.
 *  Mikael Pettersson	: Power Management for local APIC NMI watchdog.
 *  Mikael Pettersson	: Pentium 4 support for local APIC NMI watchdog.
 *  Pavel Machek and
 *  Mikael Pettersson	: PM converted to driver model. Disable/enable API.
 */

#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/nmi.h>
#include <linux/sysdev.h>
#include <linux/sysctl.h>
#include <linux/percpu.h>
#include <linux/dmi.h>
#include <linux/kprobes.h>
#include <linux/cpumask.h>

#include <asm/smp.h>
#include <asm/nmi.h>
#include <asm/kdebug.h>
#include <asm/intel_arch_perfmon.h>

#include "mach_traps.h"

int unknown_nmi_panic;
int nmi_watchdog_enabled;

/* perfctr_nmi_owner tracks the ownership of the perfctr registers:
 * evtsel_nmi_owner tracks the ownership of the event selection
 * - different performance counters/ event selection may be reserved for
 *   different subsystems this reservation system just tries to coordinate
 *   things a little
 */
static DEFINE_PER_CPU(unsigned long, perfctr_nmi_owner);
static DEFINE_PER_CPU(unsigned long, evntsel_nmi_owner[3]);

static cpumask_t backtrace_mask = CPU_MASK_NONE;

/* this number is calculated from Intel's MSR_P4_CRU_ESCR5 register and it's
 * offset from MSR_P4_BSU_ESCR0.  It will be the max for all platforms (for now)
 */
#define NMI_MAX_COUNTER_BITS 66

/* nmi_active:
 * >0: the lapic NMI watchdog is active, but can be disabled
 * <0: the lapic NMI watchdog has not been set up, and cannot
 *     be enabled
 *  0: the lapic NMI watchdog is disabled, but can be enabled
 */
atomic_t nmi_active = ATOMIC_INIT(0);		/* oprofile uses this */

unsigned int nmi_watchdog = NMI_DEFAULT;
static unsigned int nmi_hz = HZ;

struct nmi_watchdog_ctlblk {
	int enabled;
	u64 check_bit;
	unsigned int cccr_msr;
	unsigned int perfctr_msr;  /* the MSR to reset in NMI handler */
	unsigned int evntsel_msr;  /* the MSR to select the events to handle */
};
static DEFINE_PER_CPU(struct nmi_watchdog_ctlblk, nmi_watchdog_ctlblk);

/* local prototypes */
static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu);

extern void show_registers(struct pt_regs *regs);
extern int unknown_nmi_panic;

/* converts an msr to an appropriate reservation bit */
static inline unsigned int nmi_perfctr_msr_to_bit(unsigned int msr)
{
	/* returns the bit offset of the performance counter register */
	switch (boot_cpu_data.x86_vendor) {
	case X86_VENDOR_AMD:
		return (msr - MSR_K7_PERFCTR0);
	case X86_VENDOR_INTEL:
		if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON))
			return (msr - MSR_ARCH_PERFMON_PERFCTR0);

		switch (boot_cpu_data.x86) {
		case 6:
			return (msr - MSR_P6_PERFCTR0);
		case 15:
			return (msr - MSR_P4_BPU_PERFCTR0);
		}
	}
	return 0;
}

/* converts an msr to an appropriate reservation bit */
static inline unsigned int nmi_evntsel_msr_to_bit(unsigned int msr)
{
	/* returns the bit offset of the event selection register */
	switch (boot_cpu_data.x86_vendor) {
	case X86_VENDOR_AMD:
		return (msr - MSR_K7_EVNTSEL0);
	case X86_VENDOR_INTEL:
		if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON))
			return (msr - MSR_ARCH_PERFMON_EVENTSEL0);

		switch (boot_cpu_data.x86) {
		case 6:
			return (msr - MSR_P6_EVNTSEL0);
		case 15:
			return (msr - MSR_P4_BSU_ESCR0);
		}
	}
	return 0;
}

/* checks for a bit availability (hack for oprofile) */
int avail_to_resrv_perfctr_nmi_bit(unsigned int counter)
{
	BUG_ON(counter > NMI_MAX_COUNTER_BITS);

	return (!test_bit(counter, &__get_cpu_var(perfctr_nmi_owner)));
}

/* checks the an msr for availability */
int avail_to_resrv_perfctr_nmi(unsigned int msr)
{
	unsigned int counter;

	counter = nmi_perfctr_msr_to_bit(msr);
	BUG_ON(counter > NMI_MAX_COUNTER_BITS);

	return (!test_bit(counter, &__get_cpu_var(perfctr_nmi_owner)));
}

int reserve_perfctr_nmi(unsigned int msr)
{
	unsigned int counter;

	counter = nmi_perfctr_msr_to_bit(msr);
	BUG_ON(counter > NMI_MAX_COUNTER_BITS);

	if (!test_and_set_bit(counter, &__get_cpu_var(perfctr_nmi_owner)))
		return 1;
	return 0;
}

void release_perfctr_nmi(unsigned int msr)
{
	unsigned int counter;

	counter = nmi_perfctr_msr_to_bit(msr);
	BUG_ON(counter > NMI_MAX_COUNTER_BITS);

	clear_bit(counter, &__get_cpu_var(perfctr_nmi_owner));
}

int reserve_evntsel_nmi(unsigned int msr)
{
	unsigned int counter;

	counter = nmi_evntsel_msr_to_bit(msr);
	BUG_ON(counter > NMI_MAX_COUNTER_BITS);

	if (!test_and_set_bit(counter, &__get_cpu_var(evntsel_nmi_owner)[0]))
		return 1;
	return 0;
}

void release_evntsel_nmi(unsigned int msr)
{
	unsigned int counter;

	counter = nmi_evntsel_msr_to_bit(msr);
	BUG_ON(counter > NMI_MAX_COUNTER_BITS);

	clear_bit(counter, &__get_cpu_var(evntsel_nmi_owner)[0]);
}

static __cpuinit inline int nmi_known_cpu(void)
{
	switch (boot_cpu_data.x86_vendor) {
	case X86_VENDOR_AMD:
		return ((boot_cpu_data.x86 == 15) || (boot_cpu_data.x86 == 6));
	case X86_VENDOR_INTEL:
		if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON))
			return 1;
		else
			return ((boot_cpu_data.x86 == 15) || (boot_cpu_data.x86 == 6));
	}
	return 0;
}

#ifdef CONFIG_SMP
/* The performance counters used by NMI_LOCAL_APIC don't trigger when
 * the CPU is idle. To make sure the NMI watchdog really ticks on all
 * CPUs during the test make them busy.
 */
static __init void nmi_cpu_busy(void *data)
{
	volatile int *endflag = data;
	local_irq_enable_in_hardirq();
	/* Intentionally don't use cpu_relax here. This is
	   to make sure that the performance counter really ticks,
	   even if there is a simulator or similar that catches the
	   pause instruction. On a real HT machine this is fine because
	   all other CPUs are busy with "useless" delay loops and don't
	   care if they get somewhat less cycles. */
	while (*endflag == 0)
		barrier();
}
#endif

static int __init check_nmi_watchdog(void)
{
	volatile int endflag = 0;
	unsigned int *prev_nmi_count;
	int cpu;

	/* Enable NMI watchdog for newer systems.
	   Probably safe on most older systems too, but let's be careful.
	   IBM ThinkPads use INT10 inside SMM and that allows early NMI inside SMM
	   which hangs the system. Disable watchdog for all thinkpads */
	if (nmi_watchdog == NMI_DEFAULT && dmi_get_year(DMI_BIOS_DATE) >= 2004 &&
		!dmi_name_in_vendors("ThinkPad"))
		nmi_watchdog = NMI_LOCAL_APIC;

	if ((nmi_watchdog == NMI_NONE) || (nmi_watchdog == NMI_DEFAULT))
		return 0;

	if (!atomic_read(&nmi_active))
		return 0;

	prev_nmi_count = kmalloc(NR_CPUS * sizeof(int), GFP_KERNEL);
	if (!prev_nmi_count)
		return -1;

	printk(KERN_INFO "Testing NMI watchdog ... ");

	if (nmi_watchdog == NMI_LOCAL_APIC)
		smp_call_function(nmi_cpu_busy, (void *)&endflag, 0, 0);

	for_each_possible_cpu(cpu)
		prev_nmi_count[cpu] = per_cpu(irq_stat, cpu).__nmi_count;
	local_irq_enable();
	mdelay((10*1000)/nmi_hz); // wait 10 ticks

	for_each_possible_cpu(cpu) {
#ifdef CONFIG_SMP
		/* Check cpu_callin_map here because that is set
		   after the timer is started. */
		if (!cpu_isset(cpu, cpu_callin_map))
			continue;
#endif
		if (!per_cpu(nmi_watchdog_ctlblk, cpu).enabled)
			continue;
		if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
			printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
				cpu,
				prev_nmi_count[cpu],
				nmi_count(cpu));
			per_cpu(nmi_watchdog_ctlblk, cpu).enabled = 0;
			atomic_dec(&nmi_active);
		}
	}
	if (!atomic_read(&nmi_active)) {
		kfree(prev_nmi_count);
		atomic_set(&nmi_active, -1);
		return -1;
	}
	endflag = 1;
	printk("OK.\n");

	/* now that we know it works we can reduce NMI frequency to
	   something more reasonable; makes a difference in some configs */
	if (nmi_watchdog == NMI_LOCAL_APIC) {
		struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

		nmi_hz = 1;
		/*
		 * On Intel CPUs with ARCH_PERFMON only 32 bits in the counter
		 * are writable, with higher bits sign extending from bit 31.
		 * So, we can only program the counter with 31 bit values and
		 * 32nd bit should be 1, for 33.. to be 1.
		 * Find the appropriate nmi_hz
		 */
	 	if (wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR0 &&
			((u64)cpu_khz * 1000) > 0x7fffffffULL) {
			u64 count = (u64)cpu_khz * 1000;
			do_div(count, 0x7fffffffUL);
			nmi_hz = count + 1;
		}
	}

	kfree(prev_nmi_count);
	return 0;
}
/* This needs to happen later in boot so counters are working */
late_initcall(check_nmi_watchdog);

static int __init setup_nmi_watchdog(char *str)
{
	int nmi;

	get_option(&str, &nmi);

	if ((nmi >= NMI_INVALID) || (nmi < NMI_NONE))
		return 0;
	/*
	 * If any other x86 CPU has a local APIC, then
	 * please test the NMI stuff there and send me the
	 * missing bits. Right now Intel P6/P4 and AMD K7 only.
	 */
	if ((nmi == NMI_LOCAL_APIC) && (nmi_known_cpu() == 0))
		return 0;  /* no lapic support */
	nmi_watchdog = nmi;
	return 1;
}

__setup("nmi_watchdog=", setup_nmi_watchdog);

static void disable_lapic_nmi_watchdog(void)
{
	BUG_ON(nmi_watchdog != NMI_LOCAL_APIC);

	if (atomic_read(&nmi_active) <= 0)
		return;

	on_each_cpu(stop_apic_nmi_watchdog, NULL, 0, 1);

	BUG_ON(atomic_read(&nmi_active) != 0);
}

static void enable_lapic_nmi_watchdog(void)
{
	BUG_ON(nmi_watchdog != NMI_LOCAL_APIC);

	/* are we already enabled */
	if (atomic_read(&nmi_active) != 0)
		return;

	/* are we lapic aware */
	if (nmi_known_cpu() <= 0)
		return;

	on_each_cpu(setup_apic_nmi_watchdog, NULL, 0, 1);
	touch_nmi_watchdog();
}

void disable_timer_nmi_watchdog(void)
{
	BUG_ON(nmi_watchdog != NMI_IO_APIC);

	if (atomic_read(&nmi_active) <= 0)
		return;

	disable_irq(0);
	on_each_cpu(stop_apic_nmi_watchdog, NULL, 0, 1);

	BUG_ON(atomic_read(&nmi_active) != 0);
}

void enable_timer_nmi_watchdog(void)
{
	BUG_ON(nmi_watchdog != NMI_IO_APIC);

	if (atomic_read(&nmi_active) == 0) {
		touch_nmi_watchdog();
		on_each_cpu(setup_apic_nmi_watchdog, NULL, 0, 1);
		enable_irq(0);
	}
}

#ifdef CONFIG_PM

static int nmi_pm_active; /* nmi_active before suspend */

static int lapic_nmi_suspend(struct sys_device *dev, pm_message_t state)
{
	/* only CPU0 goes here, other CPUs should be offline */
	nmi_pm_active = atomic_read(&nmi_active);
	stop_apic_nmi_watchdog(NULL);
	BUG_ON(atomic_read(&nmi_active) != 0);
	return 0;
}

static int lapic_nmi_resume(struct sys_device *dev)
{
	/* only CPU0 goes here, other CPUs should be offline */
	if (nmi_pm_active > 0) {
		setup_apic_nmi_watchdog(NULL);
		touch_nmi_watchdog();
	}
	return 0;
}


static struct sysdev_class nmi_sysclass = {
	set_kset_name("lapic_nmi"),
	.resume		= lapic_nmi_resume,
	.suspend	= lapic_nmi_suspend,
};

static struct sys_device device_lapic_nmi = {
	.id	= 0,
	.cls	= &nmi_sysclass,
};

static int __init init_lapic_nmi_sysfs(void)
{
	int error;

	/* should really be a BUG_ON but b/c this is an
	 * init call, it just doesn't work.  -dcz
	 */
	if (nmi_watchdog != NMI_LOCAL_APIC)
		return 0;

	if ( atomic_read(&nmi_active) < 0 )
		return 0;

	error = sysdev_class_register(&nmi_sysclass);
	if (!error)
		error = sysdev_register(&device_lapic_nmi);
	return error;
}
/* must come after the local APIC's device_initcall() */
late_initcall(init_lapic_nmi_sysfs);

#endif	/* CONFIG_PM */

/*
 * Activate the NMI watchdog via the local APIC.
 * Original code written by Keith Owens.
 */

static void write_watchdog_counter(unsigned int perfctr_msr, const char *descr)
{
	u64 count = (u64)cpu_khz * 1000;

	do_div(count, nmi_hz);
	if(descr)
		Dprintk("setting %s to -0x%08Lx\n", descr, count);
	wrmsrl(perfctr_msr, 0 - count);
}

/* Note that these events don't tick when the CPU idles. This means
   the frequency varies with CPU load. */

#define K7_EVNTSEL_ENABLE	(1 << 22)
#define K7_EVNTSEL_INT		(1 << 20)
#define K7_EVNTSEL_OS		(1 << 17)
#define K7_EVNTSEL_USR		(1 << 16)
#define K7_EVENT_CYCLES_PROCESSOR_IS_RUNNING	0x76
#define K7_NMI_EVENT		K7_EVENT_CYCLES_PROCESSOR_IS_RUNNING

static int setup_k7_watchdog(void)
{
	unsigned int perfctr_msr, evntsel_msr;
	unsigned int evntsel;
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	perfctr_msr = MSR_K7_PERFCTR0;
	evntsel_msr = MSR_K7_EVNTSEL0;
	if (!reserve_perfctr_nmi(perfctr_msr))
		goto fail;

	if (!reserve_evntsel_nmi(evntsel_msr))
		goto fail1;

	wrmsrl(perfctr_msr, 0UL);

	evntsel = K7_EVNTSEL_INT
		| K7_EVNTSEL_OS
		| K7_EVNTSEL_USR
		| K7_NMI_EVENT;

	/* setup the timer */
	wrmsr(evntsel_msr, evntsel, 0);
	write_watchdog_counter(perfctr_msr, "K7_PERFCTR0");
	apic_write(APIC_LVTPC, APIC_DM_NMI);
	evntsel |= K7_EVNTSEL_ENABLE;
	wrmsr(evntsel_msr, evntsel, 0);

	wd->perfctr_msr = perfctr_msr;
	wd->evntsel_msr = evntsel_msr;
	wd->cccr_msr = 0;  //unused
	wd->check_bit = 1ULL<<63;
	return 1;
fail1:
	release_perfctr_nmi(perfctr_msr);
fail:
	return 0;
}

static void stop_k7_watchdog(void)
{
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	wrmsr(wd->evntsel_msr, 0, 0);

	release_evntsel_nmi(wd->evntsel_msr);
	release_perfctr_nmi(wd->perfctr_msr);
}

#define P6_EVNTSEL0_ENABLE	(1 << 22)
#define P6_EVNTSEL_INT		(1 << 20)
#define P6_EVNTSEL_OS		(1 << 17)
#define P6_EVNTSEL_USR		(1 << 16)
#define P6_EVENT_CPU_CLOCKS_NOT_HALTED	0x79
#define P6_NMI_EVENT		P6_EVENT_CPU_CLOCKS_NOT_HALTED

static int setup_p6_watchdog(void)
{
	unsigned int perfctr_msr, evntsel_msr;
	unsigned int evntsel;
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	perfctr_msr = MSR_P6_PERFCTR0;
	evntsel_msr = MSR_P6_EVNTSEL0;
	if (!reserve_perfctr_nmi(perfctr_msr))
		goto fail;

	if (!reserve_evntsel_nmi(evntsel_msr))
		goto fail1;

	wrmsrl(perfctr_msr, 0UL);

	evntsel = P6_EVNTSEL_INT
		| P6_EVNTSEL_OS
		| P6_EVNTSEL_USR
		| P6_NMI_EVENT;

	/* setup the timer */
	wrmsr(evntsel_msr, evntsel, 0);
	write_watchdog_counter(perfctr_msr, "P6_PERFCTR0");
	apic_write(APIC_LVTPC, APIC_DM_NMI);
	evntsel |= P6_EVNTSEL0_ENABLE;
	wrmsr(evntsel_msr, evntsel, 0);

	wd->perfctr_msr = perfctr_msr;
	wd->evntsel_msr = evntsel_msr;
	wd->cccr_msr = 0;  //unused
	wd->check_bit = 1ULL<<39;
	return 1;
fail1:
	release_perfctr_nmi(perfctr_msr);
fail:
	return 0;
}

static void stop_p6_watchdog(void)
{
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	wrmsr(wd->evntsel_msr, 0, 0);

	release_evntsel_nmi(wd->evntsel_msr);
	release_perfctr_nmi(wd->perfctr_msr);
}

/* Note that these events don't tick when the CPU idles. This means
   the frequency varies with CPU load. */

#define MSR_P4_MISC_ENABLE_PERF_AVAIL	(1<<7)
#define P4_ESCR_EVENT_SELECT(N)	((N)<<25)
#define P4_ESCR_OS		(1<<3)
#define P4_ESCR_USR		(1<<2)
#define P4_CCCR_OVF_PMI0	(1<<26)
#define P4_CCCR_OVF_PMI1	(1<<27)
#define P4_CCCR_THRESHOLD(N)	((N)<<20)
#define P4_CCCR_COMPLEMENT	(1<<19)
#define P4_CCCR_COMPARE		(1<<18)
#define P4_CCCR_REQUIRED	(3<<16)
#define P4_CCCR_ESCR_SELECT(N)	((N)<<13)
#define P4_CCCR_ENABLE		(1<<12)
#define P4_CCCR_OVF 		(1<<31)
/* Set up IQ_COUNTER0 to behave like a clock, by having IQ_CCCR0 filter
   CRU_ESCR0 (with any non-null event selector) through a complemented
   max threshold. [IA32-Vol3, Section 14.9.9] */

static int setup_p4_watchdog(void)
{
	unsigned int perfctr_msr, evntsel_msr, cccr_msr;
	unsigned int evntsel, cccr_val;
	unsigned int misc_enable, dummy;
	unsigned int ht_num;
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	rdmsr(MSR_IA32_MISC_ENABLE, misc_enable, dummy);
	if (!(misc_enable & MSR_P4_MISC_ENABLE_PERF_AVAIL))
		return 0;

#ifdef CONFIG_SMP
	/* detect which hyperthread we are on */
	if (smp_num_siblings == 2) {
		unsigned int ebx, apicid;

        	ebx = cpuid_ebx(1);
	        apicid = (ebx >> 24) & 0xff;
        	ht_num = apicid & 1;
	} else
#endif
		ht_num = 0;

	/* performance counters are shared resources
	 * assign each hyperthread its own set
	 * (re-use the ESCR0 register, seems safe
	 * and keeps the cccr_val the same)
	 */
	if (!ht_num) {
		/* logical cpu 0 */
		perfctr_msr = MSR_P4_IQ_PERFCTR0;
		evntsel_msr = MSR_P4_CRU_ESCR0;
		cccr_msr = MSR_P4_IQ_CCCR0;
		cccr_val = P4_CCCR_OVF_PMI0 | P4_CCCR_ESCR_SELECT(4);
	} else {
		/* logical cpu 1 */
		perfctr_msr = MSR_P4_IQ_PERFCTR1;
		evntsel_msr = MSR_P4_CRU_ESCR0;
		cccr_msr = MSR_P4_IQ_CCCR1;
		cccr_val = P4_CCCR_OVF_PMI1 | P4_CCCR_ESCR_SELECT(4);
	}

	if (!reserve_perfctr_nmi(perfctr_msr))
		goto fail;

	if (!reserve_evntsel_nmi(evntsel_msr))
		goto fail1;

	evntsel = P4_ESCR_EVENT_SELECT(0x3F)
	 	| P4_ESCR_OS
		| P4_ESCR_USR;

	cccr_val |= P4_CCCR_THRESHOLD(15)
		 | P4_CCCR_COMPLEMENT
		 | P4_CCCR_COMPARE
		 | P4_CCCR_REQUIRED;

	wrmsr(evntsel_msr, evntsel, 0);
	wrmsr(cccr_msr, cccr_val, 0);
	write_watchdog_counter(perfctr_msr, "P4_IQ_COUNTER0");
	apic_write(APIC_LVTPC, APIC_DM_NMI);
	cccr_val |= P4_CCCR_ENABLE;
	wrmsr(cccr_msr, cccr_val, 0);
	wd->perfctr_msr = perfctr_msr;
	wd->evntsel_msr = evntsel_msr;
	wd->cccr_msr = cccr_msr;
	wd->check_bit = 1ULL<<39;
	return 1;
fail1:
	release_perfctr_nmi(perfctr_msr);
fail:
	return 0;
}

static void stop_p4_watchdog(void)
{
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	wrmsr(wd->cccr_msr, 0, 0);
	wrmsr(wd->evntsel_msr, 0, 0);

	release_evntsel_nmi(wd->evntsel_msr);
	release_perfctr_nmi(wd->perfctr_msr);
}

#define ARCH_PERFMON_NMI_EVENT_SEL	ARCH_PERFMON_UNHALTED_CORE_CYCLES_SEL
#define ARCH_PERFMON_NMI_EVENT_UMASK	ARCH_PERFMON_UNHALTED_CORE_CYCLES_UMASK

static int setup_intel_arch_watchdog(void)
{
	unsigned int ebx;
	union cpuid10_eax eax;
	unsigned int unused;
	unsigned int perfctr_msr, evntsel_msr;
	unsigned int evntsel;
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	/*
	 * Check whether the Architectural PerfMon supports
	 * Unhalted Core Cycles Event or not.
	 * NOTE: Corresponding bit = 0 in ebx indicates event present.
	 */
	cpuid(10, &(eax.full), &ebx, &unused, &unused);
	if ((eax.split.mask_length < (ARCH_PERFMON_UNHALTED_CORE_CYCLES_INDEX+1)) ||
	    (ebx & ARCH_PERFMON_UNHALTED_CORE_CYCLES_PRESENT))
		goto fail;

	perfctr_msr = MSR_ARCH_PERFMON_PERFCTR0;
	evntsel_msr = MSR_ARCH_PERFMON_EVENTSEL0;

	if (!reserve_perfctr_nmi(perfctr_msr))
		goto fail;

	if (!reserve_evntsel_nmi(evntsel_msr))
		goto fail1;

	wrmsrl(perfctr_msr, 0UL);

	evntsel = ARCH_PERFMON_EVENTSEL_INT
		| ARCH_PERFMON_EVENTSEL_OS
		| ARCH_PERFMON_EVENTSEL_USR
		| ARCH_PERFMON_NMI_EVENT_SEL
		| ARCH_PERFMON_NMI_EVENT_UMASK;

	/* setup the timer */
	wrmsr(evntsel_msr, evntsel, 0);
	write_watchdog_counter(perfctr_msr, "INTEL_ARCH_PERFCTR0");
	apic_write(APIC_LVTPC, APIC_DM_NMI);
	evntsel |= ARCH_PERFMON_EVENTSEL0_ENABLE;
	wrmsr(evntsel_msr, evntsel, 0);

	wd->perfctr_msr = perfctr_msr;
	wd->evntsel_msr = evntsel_msr;
	wd->cccr_msr = 0;  //unused
	wd->check_bit = 1ULL << (eax.split.bit_width - 1);
	return 1;
fail1:
	release_perfctr_nmi(perfctr_msr);
fail:
	return 0;
}

static void stop_intel_arch_watchdog(void)
{
	unsigned int ebx;
	union cpuid10_eax eax;
	unsigned int unused;
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	/*
	 * Check whether the Architectural PerfMon supports
	 * Unhalted Core Cycles Event or not.
	 * NOTE: Corresponding bit = 0 in ebx indicates event present.
	 */
	cpuid(10, &(eax.full), &ebx, &unused, &unused);
	if ((eax.split.mask_length < (ARCH_PERFMON_UNHALTED_CORE_CYCLES_INDEX+1)) ||
	    (ebx & ARCH_PERFMON_UNHALTED_CORE_CYCLES_PRESENT))
		return;

	wrmsr(wd->evntsel_msr, 0, 0);
	release_evntsel_nmi(wd->evntsel_msr);
	release_perfctr_nmi(wd->perfctr_msr);
}

void setup_apic_nmi_watchdog (void *unused)
{
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	/* only support LOCAL and IO APICs for now */
	if ((nmi_watchdog != NMI_LOCAL_APIC) &&
	    (nmi_watchdog != NMI_IO_APIC))
	    	return;

	if (wd->enabled == 1)
		return;

	/* cheap hack to support suspend/resume */
	/* if cpu0 is not active neither should the other cpus */
	if ((smp_processor_id() != 0) && (atomic_read(&nmi_active) <= 0))
		return;

	if (nmi_watchdog == NMI_LOCAL_APIC) {
		switch (boot_cpu_data.x86_vendor) {
		case X86_VENDOR_AMD:
			if (boot_cpu_data.x86 != 6 && boot_cpu_data.x86 != 15)
				return;
			if (!setup_k7_watchdog())
				return;
			break;
		case X86_VENDOR_INTEL:
			if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
				if (!setup_intel_arch_watchdog())
					return;
				break;
			}
			switch (boot_cpu_data.x86) {
			case 6:
				if (boot_cpu_data.x86_model > 0xd)
					return;

				if (!setup_p6_watchdog())
					return;
				break;
			case 15:
				if (boot_cpu_data.x86_model > 0x4)
					return;

				if (!setup_p4_watchdog())
					return;
				break;
			default:
				return;
			}
			break;
		default:
			return;
		}
	}
	wd->enabled = 1;
	atomic_inc(&nmi_active);
}

void stop_apic_nmi_watchdog(void *unused)
{
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);

	/* only support LOCAL and IO APICs for now */
	if ((nmi_watchdog != NMI_LOCAL_APIC) &&
	    (nmi_watchdog != NMI_IO_APIC))
	    	return;

	if (wd->enabled == 0)
		return;

	if (nmi_watchdog == NMI_LOCAL_APIC) {
		switch (boot_cpu_data.x86_vendor) {
		case X86_VENDOR_AMD:
			stop_k7_watchdog();
			break;
		case X86_VENDOR_INTEL:
			if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
				stop_intel_arch_watchdog();
				break;
			}
			switch (boot_cpu_data.x86) {
			case 6:
				if (boot_cpu_data.x86_model > 0xd)
					break;
				stop_p6_watchdog();
				break;
			case 15:
				if (boot_cpu_data.x86_model > 0x4)
					break;
				stop_p4_watchdog();
				break;
			}
			break;
		default:
			return;
		}
	}
	wd->enabled = 0;
	atomic_dec(&nmi_active);
}

/*
 * the best way to detect whether a CPU has a 'hard lockup' problem
 * is to check it's local APIC timer IRQ counts. If they are not
 * changing then that CPU has some problem.
 *
 * as these watchdog NMI IRQs are generated on every CPU, we only
 * have to check the current processor.
 *
 * since NMIs don't listen to _any_ locks, we have to be extremely
 * careful not to rely on unsafe variables. The printk might lock
 * up though, so we have to break up any console locks first ...
 * [when there will be more tty-related locks, break them up
 *  here too!]
 */

static unsigned int
	last_irq_sums [NR_CPUS],
	alert_counter [NR_CPUS];

void touch_nmi_watchdog (void)
{
	int i;

	/*
	 * Just reset the alert counters, (other CPUs might be
	 * spinning on locks we hold):
	 */
	for_each_possible_cpu(i)
		alert_counter[i] = 0;

	/*
	 * Tickle the softlockup detector too:
	 */
	touch_softlockup_watchdog();
}
EXPORT_SYMBOL(touch_nmi_watchdog);

extern void die_nmi(struct pt_regs *, const char *msg);

__kprobes int nmi_watchdog_tick(struct pt_regs * regs, unsigned reason)
{

	/*
	 * Since current_thread_info()-> is always on the stack, and we
	 * always switch the stack NMI-atomically, it's safe to use
	 * smp_processor_id().
	 */
	unsigned int sum;
	int touched = 0;
	int cpu = smp_processor_id();
	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
	u64 dummy;
	int rc=0;

	/* check for other users first */
	if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
			== NOTIFY_STOP) {
		rc = 1;
		touched = 1;
	}

	if (cpu_isset(cpu, backtrace_mask)) {
		static DEFINE_SPINLOCK(lock);	/* Serialise the printks */

		spin_lock(&lock);
		printk("NMI backtrace for cpu %d\n", cpu);
		dump_stack();
		spin_unlock(&lock);
		cpu_clear(cpu, backtrace_mask);
	}

	sum = per_cpu(irq_stat, cpu).apic_timer_irqs;

	/* if the apic timer isn't firing, this cpu isn't doing much */
	if (!touched && last_irq_sums[cpu] == sum) {
		/*
		 * Ayiee, looks like this CPU is stuck ...
		 * wait a few IRQs (5 seconds) before doing the oops ...
		 */
		alert_counter[cpu]++;
		if (alert_counter[cpu] == 5*nmi_hz)
			/*
			 * die_nmi will return ONLY if NOTIFY_STOP happens..
			 */
			die_nmi(regs, "BUG: NMI Watchdog detected LOCKUP");
	} else {
		last_irq_sums[cpu] = sum;
		alert_counter[cpu] = 0;
	}
	/* see if the nmi watchdog went off */
	if (wd->enabled) {
		if (nmi_watchdog == NMI_LOCAL_APIC) {
			rdmsrl(wd->perfctr_msr, dummy);
			if (dummy & wd->check_bit){
				/* this wasn't a watchdog timer interrupt */
				goto done;
			}

			/* only Intel P4 uses the cccr msr */
	 		if (wd->cccr_msr != 0) {
	 			/*
	 			 * P4 quirks:
	 			 * - An overflown perfctr will assert its interrupt
	 			 *   until the OVF flag in its CCCR is cleared.
	 			 * - LVTPC is masked on interrupt and must be
	 			 *   unmasked by the LVTPC handler.
	 			 */
				rdmsrl(wd->cccr_msr, dummy);
				dummy &= ~P4_CCCR_OVF;
	 			wrmsrl(wd->cccr_msr, dummy);
	 			apic_write(APIC_LVTPC, APIC_DM_NMI);
	 		}
			else if (wd->perfctr_msr == MSR_P6_PERFCTR0 ||
				 wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR0) {
				/* P6 based Pentium M need to re-unmask
				 * the apic vector but it doesn't hurt
				 * other P6 variant.
				 * ArchPerfom/Core Duo also needs this */
				apic_write(APIC_LVTPC, APIC_DM_NMI);
			}
			/* start the cycle over again */
			write_watchdog_counter(wd->perfctr_msr, NULL);
			rc = 1;
		} else if (nmi_watchdog == NMI_IO_APIC) {
			/* don't know how to accurately check for this.
			 * just assume it was a watchdog timer interrupt
			 * This matches the old behaviour.
			 */
			rc = 1;
		}
	}
done:
	return rc;
}

int do_nmi_callback(struct pt_regs * regs, int cpu)
{
#ifdef CONFIG_SYSCTL
	if (unknown_nmi_panic)
		return unknown_nmi_panic_callback(regs, cpu);
#endif
	return 0;
}

#ifdef CONFIG_SYSCTL

static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu)
{
	unsigned char reason = get_nmi_reason();
	char buf[64];

	sprintf(buf, "NMI received for unknown reason %02x\n", reason);
	die_nmi(regs, buf);
	return 0;
}

/*
 * proc handler for /proc/sys/kernel/nmi
 */
int proc_nmi_enabled(struct ctl_table *table, int write, struct file *file,
			void __user *buffer, size_t *length, loff_t *ppos)
{
	int old_state;

	nmi_watchdog_enabled = (atomic_read(&nmi_active) > 0) ? 1 : 0;
	old_state = nmi_watchdog_enabled;
	proc_dointvec(table, write, file, buffer, length, ppos);
	if (!!old_state == !!nmi_watchdog_enabled)
		return 0;

	if (atomic_read(&nmi_active) < 0) {
		printk( KERN_WARNING "NMI watchdog is permanently disabled\n");
		return -EIO;
	}

	if (nmi_watchdog == NMI_DEFAULT) {
		if (nmi_known_cpu() > 0)
			nmi_watchdog = NMI_LOCAL_APIC;
		else
			nmi_watchdog = NMI_IO_APIC;
	}

	if (nmi_watchdog == NMI_LOCAL_APIC) {
		if (nmi_watchdog_enabled)
			enable_lapic_nmi_watchdog();
		else
			disable_lapic_nmi_watchdog();
	} else {
		printk( KERN_WARNING
			"NMI watchdog doesn't know what hardware to touch\n");
		return -EIO;
	}
	return 0;
}

#endif

void __trigger_all_cpu_backtrace(void)
{
	int i;

	backtrace_mask = cpu_online_map;
	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
	for (i = 0; i < 10 * 1000; i++) {
		if (cpus_empty(backtrace_mask))
			break;
		mdelay(1);
	}
}

EXPORT_SYMBOL(nmi_active);
EXPORT_SYMBOL(nmi_watchdog);
EXPORT_SYMBOL(avail_to_resrv_perfctr_nmi);
EXPORT_SYMBOL(avail_to_resrv_perfctr_nmi_bit);
EXPORT_SYMBOL(reserve_perfctr_nmi);
EXPORT_SYMBOL(release_perfctr_nmi);
EXPORT_SYMBOL(reserve_evntsel_nmi);
EXPORT_SYMBOL(release_evntsel_nmi);
EXPORT_SYMBOL(disable_timer_nmi_watchdog);
EXPORT_SYMBOL(enable_timer_nmi_watchdog);