x86, mce: add MCE poll count to /proc/interrupts

[linux-2.6/mini2440.git] / arch / x86 / kernel / cpu / mcheck / mce.c

/*
 * Machine check handler.
 *
 * K8 parts Copyright 2002,2003 Andi Kleen, SuSE Labs.
 * Rest from unknown author(s).
 * 2004 Andi Kleen. Rewrote most of it.
 * Copyright 2008 Intel Corporation
 * Author: Andi Kleen
 */
#include <linux/thread_info.h>
#include <linux/capability.h>
#include <linux/miscdevice.h>
#include <linux/ratelimit.h>
#include <linux/kallsyms.h>
#include <linux/rcupdate.h>
#include <linux/kobject.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/string.h>
#include <linux/sysdev.h>
#include <linux/ctype.h>
#include <linux/sched.h>
#include <linux/sysfs.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/kmod.h>
#include <linux/poll.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/fs.h>

#include <asm/processor.h>
#include <asm/idle.h>
#include <asm/mce.h>
#include <asm/msr.h>

#include "mce.h"

/* Handle unconfigured int18 (should never happen) */
static void unexpected_machine_check(struct pt_regs *regs, long error_code)
{
        printk(KERN_ERR "CPU#%d: Unexpected int18 (Machine Check).\n",
               smp_processor_id());
}

/* Call the installed machine check handler for this CPU setup. */
void (*machine_check_vector)(struct pt_regs *, long error_code) =
                                                unexpected_machine_check;

int                             mce_disabled;

#ifdef CONFIG_X86_NEW_MCE

#define MISC_MCELOG_MINOR       227

atomic_t mce_entry;

DEFINE_PER_CPU(unsigned, mce_exception_count);

/*
 * Tolerant levels:
 *   0: always panic on uncorrected errors, log corrected errors
 *   1: panic or SIGBUS on uncorrected errors, log corrected errors
 *   2: SIGBUS or log uncorrected errors (if possible), log corrected errors
 *   3: never panic or SIGBUS, log all errors (for testing only)
 */
static int                      tolerant = 1;
static int                      banks;
static u64                      *bank;
static unsigned long            notify_user;
static int                      rip_msr;
static int                      mce_bootlog = -1;

static char                     trigger[128];
static char                     *trigger_argv[2] = { trigger, NULL };

static unsigned long            dont_init_banks;

static DECLARE_WAIT_QUEUE_HEAD(mce_wait);

/* MCA banks polled by the period polling timer for corrected events */
DEFINE_PER_CPU(mce_banks_t, mce_poll_banks) = {
        [0 ... BITS_TO_LONGS(MAX_NR_BANKS)-1] = ~0UL
};

static inline int skip_bank_init(int i)
{
        return i < BITS_PER_LONG && test_bit(i, &dont_init_banks);
}

/* Do initial initialization of a struct mce */
void mce_setup(struct mce *m)
{
        memset(m, 0, sizeof(struct mce));
        m->cpu = smp_processor_id();
        rdtscll(m->tsc);
}

DEFINE_PER_CPU(struct mce, injectm);
EXPORT_PER_CPU_SYMBOL_GPL(injectm);

/*
 * Lockless MCE logging infrastructure.
 * This avoids deadlocks on printk locks without having to break locks. Also
 * separate MCEs from kernel messages to avoid bogus bug reports.
 */

static struct mce_log mcelog = {
        MCE_LOG_SIGNATURE,
        MCE_LOG_LEN,
};

void mce_log(struct mce *mce)
{
        unsigned next, entry;

        mce->finished = 0;
        wmb();
        for (;;) {
                entry = rcu_dereference(mcelog.next);
                for (;;) {
                        /*
                         * When the buffer fills up discard new entries.
                         * Assume that the earlier errors are the more
                         * interesting ones:
                         */
                        if (entry >= MCE_LOG_LEN) {
                                set_bit(MCE_OVERFLOW,
                                        (unsigned long *)&mcelog.flags);
                                return;
                        }
                        /* Old left over entry. Skip: */
                        if (mcelog.entry[entry].finished) {
                                entry++;
                                continue;
                        }
                        break;
                }
                smp_rmb();
                next = entry + 1;
                if (cmpxchg(&mcelog.next, entry, next) == entry)
                        break;
        }
        memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
        wmb();
        mcelog.entry[entry].finished = 1;
        wmb();

        set_bit(0, &notify_user);
}

static void print_mce(struct mce *m)
{
        printk(KERN_EMERG "\n"
               KERN_EMERG "HARDWARE ERROR\n"
               KERN_EMERG
               "CPU %d: Machine Check Exception: %16Lx Bank %d: %016Lx\n",
               m->cpu, m->mcgstatus, m->bank, m->status);
        if (m->ip) {
                printk(KERN_EMERG "RIP%s %02x:<%016Lx> ",
                       !(m->mcgstatus & MCG_STATUS_EIPV) ? " !INEXACT!" : "",
                       m->cs, m->ip);
                if (m->cs == __KERNEL_CS)
                        print_symbol("{%s}", m->ip);
                printk("\n");
        }
        printk(KERN_EMERG "TSC %llx ", m->tsc);
        if (m->addr)
                printk("ADDR %llx ", m->addr);
        if (m->misc)
                printk("MISC %llx ", m->misc);
        printk("\n");
        printk(KERN_EMERG "This is not a software problem!\n");
        printk(KERN_EMERG "Run through mcelog --ascii to decode "
               "and contact your hardware vendor\n");
}

static void mce_panic(char *msg, struct mce *backup, u64 start)
{
        int i;

        bust_spinlocks(1);
        console_verbose();
        for (i = 0; i < MCE_LOG_LEN; i++) {
                u64 tsc = mcelog.entry[i].tsc;

                if ((s64)(tsc - start) < 0)
                        continue;
                print_mce(&mcelog.entry[i]);
                if (backup && mcelog.entry[i].tsc == backup->tsc)
                        backup = NULL;
        }
        if (backup)
                print_mce(backup);
        panic(msg);
}

/* Support code for software error injection */

static int msr_to_offset(u32 msr)
{
        unsigned bank = __get_cpu_var(injectm.bank);
        if (msr == rip_msr)
                return offsetof(struct mce, ip);
        if (msr == MSR_IA32_MC0_STATUS + bank*4)
                return offsetof(struct mce, status);
        if (msr == MSR_IA32_MC0_ADDR + bank*4)
                return offsetof(struct mce, addr);
        if (msr == MSR_IA32_MC0_MISC + bank*4)
                return offsetof(struct mce, misc);
        if (msr == MSR_IA32_MCG_STATUS)
                return offsetof(struct mce, mcgstatus);
        return -1;
}

/* MSR access wrappers used for error injection */
static u64 mce_rdmsrl(u32 msr)
{
        u64 v;
        if (__get_cpu_var(injectm).finished) {
                int offset = msr_to_offset(msr);
                if (offset < 0)
                        return 0;
                return *(u64 *)((char *)&__get_cpu_var(injectm) + offset);
        }
        rdmsrl(msr, v);
        return v;
}

static void mce_wrmsrl(u32 msr, u64 v)
{
        if (__get_cpu_var(injectm).finished) {
                int offset = msr_to_offset(msr);
                if (offset >= 0)
                        *(u64 *)((char *)&__get_cpu_var(injectm) + offset) = v;
                return;
        }
        wrmsrl(msr, v);
}

int mce_available(struct cpuinfo_x86 *c)
{
        if (mce_disabled)
                return 0;
        return cpu_has(c, X86_FEATURE_MCE) && cpu_has(c, X86_FEATURE_MCA);
}

static inline void mce_get_rip(struct mce *m, struct pt_regs *regs)
{
        if (regs && (m->mcgstatus & MCG_STATUS_RIPV)) {
                m->ip = regs->ip;
                m->cs = regs->cs;
        } else {
                m->ip = 0;
                m->cs = 0;
        }
        if (rip_msr) {
                /* Assume the RIP in the MSR is exact. Is this true? */
                m->mcgstatus |= MCG_STATUS_EIPV;
                m->ip = mce_rdmsrl(rip_msr);
                m->cs = 0;
        }
}

DEFINE_PER_CPU(unsigned, mce_poll_count);

/*
 * Poll for corrected events or events that happened before reset.
 * Those are just logged through /dev/mcelog.
 *
 * This is executed in standard interrupt context.
 */
void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
{
        struct mce m;
        int i;

        __get_cpu_var(mce_poll_count)++;

        mce_setup(&m);

        m.mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
        for (i = 0; i < banks; i++) {
                if (!bank[i] || !test_bit(i, *b))
                        continue;

                m.misc = 0;
                m.addr = 0;
                m.bank = i;
                m.tsc = 0;

                barrier();
                m.status = mce_rdmsrl(MSR_IA32_MC0_STATUS + i*4);
                if (!(m.status & MCI_STATUS_VAL))
                        continue;

                /*
                 * Uncorrected events are handled by the exception handler
                 * when it is enabled. But when the exception is disabled log
                 * everything.
                 *
                 * TBD do the same check for MCI_STATUS_EN here?
                 */
                if ((m.status & MCI_STATUS_UC) && !(flags & MCP_UC))
                        continue;

                if (m.status & MCI_STATUS_MISCV)
                        m.misc = mce_rdmsrl(MSR_IA32_MC0_MISC + i*4);
                if (m.status & MCI_STATUS_ADDRV)
                        m.addr = mce_rdmsrl(MSR_IA32_MC0_ADDR + i*4);

                if (!(flags & MCP_TIMESTAMP))
                        m.tsc = 0;
                /*
                 * Don't get the IP here because it's unlikely to
                 * have anything to do with the actual error location.
                 */
                if (!(flags & MCP_DONTLOG)) {
                        mce_log(&m);
                        add_taint(TAINT_MACHINE_CHECK);
                }

                /*
                 * Clear state for this bank.
                 */
                mce_wrmsrl(MSR_IA32_MC0_STATUS+4*i, 0);
        }

        /*
         * Don't clear MCG_STATUS here because it's only defined for
         * exceptions.
         */

        sync_core();
}
EXPORT_SYMBOL_GPL(machine_check_poll);

/*
 * The actual machine check handler. This only handles real
 * exceptions when something got corrupted coming in through int 18.
 *
 * This is executed in NMI context not subject to normal locking rules. This
 * implies that most kernel services cannot be safely used. Don't even
 * think about putting a printk in there!
 */
void do_machine_check(struct pt_regs *regs, long error_code)
{
        struct mce m, panicm;
        int panicm_found = 0;
        u64 mcestart = 0;
        int i;
        /*
         * If no_way_out gets set, there is no safe way to recover from this
         * MCE.  If tolerant is cranked up, we'll try anyway.
         */
        int no_way_out = 0;
        /*
         * If kill_it gets set, there might be a way to recover from this
         * error.
         */
        int kill_it = 0;
        DECLARE_BITMAP(toclear, MAX_NR_BANKS);

        atomic_inc(&mce_entry);

        __get_cpu_var(mce_exception_count)++;

        if (notify_die(DIE_NMI, "machine check", regs, error_code,
                           18, SIGKILL) == NOTIFY_STOP)
                goto out;
        if (!banks)
                goto out;

        mce_setup(&m);

        m.mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);

        /* if the restart IP is not valid, we're done for */
        if (!(m.mcgstatus & MCG_STATUS_RIPV))
                no_way_out = 1;

        rdtscll(mcestart);
        barrier();

        for (i = 0; i < banks; i++) {
                __clear_bit(i, toclear);
                if (!bank[i])
                        continue;

                m.misc = 0;
                m.addr = 0;
                m.bank = i;

                m.status = mce_rdmsrl(MSR_IA32_MC0_STATUS + i*4);
                if ((m.status & MCI_STATUS_VAL) == 0)
                        continue;

                /*
                 * Non uncorrected errors are handled by machine_check_poll
                 * Leave them alone.
                 */
                if ((m.status & MCI_STATUS_UC) == 0)
                        continue;

                /*
                 * Set taint even when machine check was not enabled.
                 */
                add_taint(TAINT_MACHINE_CHECK);

                __set_bit(i, toclear);

                if (m.status & MCI_STATUS_EN) {
                        /* if PCC was set, there's no way out */
                        no_way_out |= !!(m.status & MCI_STATUS_PCC);
                        /*
                         * If this error was uncorrectable and there was
                         * an overflow, we're in trouble.  If no overflow,
                         * we might get away with just killing a task.
                         */
                        if (m.status & MCI_STATUS_UC) {
                                if (tolerant < 1 || m.status & MCI_STATUS_OVER)
                                        no_way_out = 1;
                                kill_it = 1;
                        }
                } else {
                        /*
                         * Machine check event was not enabled. Clear, but
                         * ignore.
                         */
                        continue;
                }

                if (m.status & MCI_STATUS_MISCV)
                        m.misc = mce_rdmsrl(MSR_IA32_MC0_MISC + i*4);
                if (m.status & MCI_STATUS_ADDRV)
                        m.addr = mce_rdmsrl(MSR_IA32_MC0_ADDR + i*4);

                mce_get_rip(&m, regs);
                mce_log(&m);

                /*
                 * Did this bank cause the exception?
                 *
                 * Assume that the bank with uncorrectable errors did it,
                 * and that there is only a single one:
                 */
                if ((m.status & MCI_STATUS_UC) &&
                                        (m.status & MCI_STATUS_EN)) {
                        panicm = m;
                        panicm_found = 1;
                }
        }

        /*
         * If we didn't find an uncorrectable error, pick
         * the last one (shouldn't happen, just being safe).
         */
        if (!panicm_found)
                panicm = m;

        /*
         * If we have decided that we just CAN'T continue, and the user
         * has not set tolerant to an insane level, give up and die.
         */
        if (no_way_out && tolerant < 3)
                mce_panic("Machine check", &panicm, mcestart);

        /*
         * If the error seems to be unrecoverable, something should be
         * done.  Try to kill as little as possible.  If we can kill just
         * one task, do that.  If the user has set the tolerance very
         * high, don't try to do anything at all.
         */
        if (kill_it && tolerant < 3) {
                int user_space = 0;

                /*
                 * If the EIPV bit is set, it means the saved IP is the
                 * instruction which caused the MCE.
                 */
                if (m.mcgstatus & MCG_STATUS_EIPV)
                        user_space = panicm.ip && (panicm.cs & 3);

                /*
                 * If we know that the error was in user space, send a
                 * SIGBUS.  Otherwise, panic if tolerance is low.
                 *
                 * force_sig() takes an awful lot of locks and has a slight
                 * risk of deadlocking.
                 */
                if (user_space) {
                        force_sig(SIGBUS, current);
                } else if (panic_on_oops || tolerant < 2) {
                        mce_panic("Uncorrected machine check",
                                &panicm, mcestart);
                }
        }

        /* notify userspace ASAP */
        set_thread_flag(TIF_MCE_NOTIFY);

        /* the last thing we do is clear state */
        for (i = 0; i < banks; i++) {
                if (test_bit(i, toclear))
                        mce_wrmsrl(MSR_IA32_MC0_STATUS+4*i, 0);
        }
        mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
out:
        atomic_dec(&mce_entry);
        sync_core();
}
EXPORT_SYMBOL_GPL(do_machine_check);

#ifdef CONFIG_X86_MCE_INTEL
/***
 * mce_log_therm_throt_event - Logs the thermal throttling event to mcelog
 * @cpu: The CPU on which the event occurred.
 * @status: Event status information
 *
 * This function should be called by the thermal interrupt after the
 * event has been processed and the decision was made to log the event
 * further.
 *
 * The status parameter will be saved to the 'status' field of 'struct mce'
 * and historically has been the register value of the
 * MSR_IA32_THERMAL_STATUS (Intel) msr.
 */
void mce_log_therm_throt_event(__u64 status)
{
        struct mce m;

        mce_setup(&m);
        m.bank = MCE_THERMAL_BANK;
        m.status = status;
        mce_log(&m);
}
#endif /* CONFIG_X86_MCE_INTEL */

/*
 * Periodic polling timer for "silent" machine check errors.  If the
 * poller finds an MCE, poll 2x faster.  When the poller finds no more
 * errors, poll 2x slower (up to check_interval seconds).
 */
static int check_interval = 5 * 60; /* 5 minutes */

static DEFINE_PER_CPU(int, next_interval); /* in jiffies */
static DEFINE_PER_CPU(struct timer_list, mce_timer);

static void mcheck_timer(unsigned long data)
{
        struct timer_list *t = &per_cpu(mce_timer, data);
        int *n;

        WARN_ON(smp_processor_id() != data);

        if (mce_available(&current_cpu_data)) {
                machine_check_poll(MCP_TIMESTAMP,
                                &__get_cpu_var(mce_poll_banks));
        }

        /*
         * Alert userspace if needed.  If we logged an MCE, reduce the
         * polling interval, otherwise increase the polling interval.
         */
        n = &__get_cpu_var(next_interval);
        if (mce_notify_user())
                *n = max(*n/2, HZ/100);
        else
                *n = min(*n*2, (int)round_jiffies_relative(check_interval*HZ));

        t->expires = jiffies + *n;
        add_timer(t);
}

static void mce_do_trigger(struct work_struct *work)
{
        call_usermodehelper(trigger, trigger_argv, NULL, UMH_NO_WAIT);
}

static DECLARE_WORK(mce_trigger_work, mce_do_trigger);

/*
 * Notify the user(s) about new machine check events.
 * Can be called from interrupt context, but not from machine check/NMI
 * context.
 */
int mce_notify_user(void)
{
        /* Not more than two messages every minute */
        static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);

        clear_thread_flag(TIF_MCE_NOTIFY);

        if (test_and_clear_bit(0, &notify_user)) {
                wake_up_interruptible(&mce_wait);

                /*
                 * There is no risk of missing notifications because
                 * work_pending is always cleared before the function is
                 * executed.
                 */
                if (trigger[0] && !work_pending(&mce_trigger_work))
                        schedule_work(&mce_trigger_work);

                if (__ratelimit(&ratelimit))
                        printk(KERN_INFO "Machine check events logged\n");

                return 1;
        }
        return 0;
}
EXPORT_SYMBOL_GPL(mce_notify_user);

/*
 * Initialize Machine Checks for a CPU.
 */
static int mce_cap_init(void)
{
        unsigned b;
        u64 cap;

        rdmsrl(MSR_IA32_MCG_CAP, cap);

        b = cap & MCG_BANKCNT_MASK;
        printk(KERN_INFO "mce: CPU supports %d MCE banks\n", b);

        if (b > MAX_NR_BANKS) {
                printk(KERN_WARNING
                       "MCE: Using only %u machine check banks out of %u\n",
                        MAX_NR_BANKS, b);
                b = MAX_NR_BANKS;
        }

        /* Don't support asymmetric configurations today */
        WARN_ON(banks != 0 && b != banks);
        banks = b;
        if (!bank) {
                bank = kmalloc(banks * sizeof(u64), GFP_KERNEL);
                if (!bank)
                        return -ENOMEM;
                memset(bank, 0xff, banks * sizeof(u64));
        }

        /* Use accurate RIP reporting if available. */
        if ((cap & MCG_EXT_P) && MCG_EXT_CNT(cap) >= 9)
                rip_msr = MSR_IA32_MCG_EIP;

        return 0;
}

static void mce_init(void)
{
        mce_banks_t all_banks;
        u64 cap;
        int i;

        /*
         * Log the machine checks left over from the previous reset.
         */
        bitmap_fill(all_banks, MAX_NR_BANKS);
        machine_check_poll(MCP_UC|(!mce_bootlog ? MCP_DONTLOG : 0), &all_banks);

        set_in_cr4(X86_CR4_MCE);

        rdmsrl(MSR_IA32_MCG_CAP, cap);
        if (cap & MCG_CTL_P)
                wrmsr(MSR_IA32_MCG_CTL, 0xffffffff, 0xffffffff);

        for (i = 0; i < banks; i++) {
                if (skip_bank_init(i))
                        continue;
                wrmsrl(MSR_IA32_MC0_CTL+4*i, bank[i]);
                wrmsrl(MSR_IA32_MC0_STATUS+4*i, 0);
        }
}

/* Add per CPU specific workarounds here */
static void mce_cpu_quirks(struct cpuinfo_x86 *c)
{
        /* This should be disabled by the BIOS, but isn't always */
        if (c->x86_vendor == X86_VENDOR_AMD) {
                if (c->x86 == 15 && banks > 4) {
                        /*
                         * disable GART TBL walk error reporting, which
                         * trips off incorrectly with the IOMMU & 3ware
                         * & Cerberus:
                         */
                        clear_bit(10, (unsigned long *)&bank[4]);
                }
                if (c->x86 <= 17 && mce_bootlog < 0) {
                        /*
                         * Lots of broken BIOS around that don't clear them
                         * by default and leave crap in there. Don't log:
                         */
                        mce_bootlog = 0;
                }
                /*
                 * Various K7s with broken bank 0 around. Always disable
                 * by default.
                 */
                 if (c->x86 == 6)
                        bank[0] = 0;
        }

        if (c->x86_vendor == X86_VENDOR_INTEL) {
                /*
                 * SDM documents that on family 6 bank 0 should not be written
                 * because it aliases to another special BIOS controlled
                 * register.
                 * But it's not aliased anymore on model 0x1a+
                 * Don't ignore bank 0 completely because there could be a
                 * valid event later, merely don't write CTL0.
                 */

                if (c->x86 == 6 && c->x86_model < 0x1A)
                        __set_bit(0, &dont_init_banks);
        }
}

static void __cpuinit mce_ancient_init(struct cpuinfo_x86 *c)
{
        if (c->x86 != 5)
                return;
        switch (c->x86_vendor) {
        case X86_VENDOR_INTEL:
                if (mce_p5_enabled())
                        intel_p5_mcheck_init(c);
                break;
        case X86_VENDOR_CENTAUR:
                winchip_mcheck_init(c);
                break;
        }
}

static void mce_cpu_features(struct cpuinfo_x86 *c)
{
        switch (c->x86_vendor) {
        case X86_VENDOR_INTEL:
                mce_intel_feature_init(c);
                break;
        case X86_VENDOR_AMD:
                mce_amd_feature_init(c);
                break;
        default:
                break;
        }
}

static void mce_init_timer(void)
{
        struct timer_list *t = &__get_cpu_var(mce_timer);
        int *n = &__get_cpu_var(next_interval);

        *n = check_interval * HZ;
        if (!*n)
                return;
        setup_timer(t, mcheck_timer, smp_processor_id());
        t->expires = round_jiffies(jiffies + *n);
        add_timer(t);
}

/*
 * Called for each booted CPU to set up machine checks.
 * Must be called with preempt off:
 */
void __cpuinit mcheck_init(struct cpuinfo_x86 *c)
{
        if (mce_disabled)
                return;

        mce_ancient_init(c);

        if (!mce_available(c))
                return;

        if (mce_cap_init() < 0) {
                mce_disabled = 1;
                return;
        }
        mce_cpu_quirks(c);

        machine_check_vector = do_machine_check;

        mce_init();
        mce_cpu_features(c);
        mce_init_timer();
}

/*
 * Character device to read and clear the MCE log.
 */

static DEFINE_SPINLOCK(mce_state_lock);
static int              open_count;             /* #times opened */
static int              open_exclu;             /* already open exclusive? */

static int mce_open(struct inode *inode, struct file *file)
{
        spin_lock(&mce_state_lock);

        if (open_exclu || (open_count && (file->f_flags & O_EXCL))) {
                spin_unlock(&mce_state_lock);

                return -EBUSY;
        }

        if (file->f_flags & O_EXCL)
                open_exclu = 1;
        open_count++;

        spin_unlock(&mce_state_lock);

        return nonseekable_open(inode, file);
}

static int mce_release(struct inode *inode, struct file *file)
{
        spin_lock(&mce_state_lock);

        open_count--;
        open_exclu = 0;

        spin_unlock(&mce_state_lock);

        return 0;
}

static void collect_tscs(void *data)
{
        unsigned long *cpu_tsc = (unsigned long *)data;

        rdtscll(cpu_tsc[smp_processor_id()]);
}

static DEFINE_MUTEX(mce_read_mutex);

static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize,
                        loff_t *off)
{
        char __user *buf = ubuf;
        unsigned long *cpu_tsc;
        unsigned prev, next;
        int i, err;

        cpu_tsc = kmalloc(nr_cpu_ids * sizeof(long), GFP_KERNEL);
        if (!cpu_tsc)
                return -ENOMEM;

        mutex_lock(&mce_read_mutex);
        next = rcu_dereference(mcelog.next);

        /* Only supports full reads right now */
        if (*off != 0 || usize < MCE_LOG_LEN*sizeof(struct mce)) {
                mutex_unlock(&mce_read_mutex);
                kfree(cpu_tsc);

                return -EINVAL;
        }

        err = 0;
        prev = 0;
        do {
                for (i = prev; i < next; i++) {
                        unsigned long start = jiffies;

                        while (!mcelog.entry[i].finished) {
                                if (time_after_eq(jiffies, start + 2)) {
                                        memset(mcelog.entry + i, 0,
                                               sizeof(struct mce));
                                        goto timeout;
                                }
                                cpu_relax();
                        }
                        smp_rmb();
                        err |= copy_to_user(buf, mcelog.entry + i,
                                            sizeof(struct mce));
                        buf += sizeof(struct mce);
timeout:
                        ;
                }

                memset(mcelog.entry + prev, 0,
                       (next - prev) * sizeof(struct mce));
                prev = next;
                next = cmpxchg(&mcelog.next, prev, 0);
        } while (next != prev);

        synchronize_sched();

        /*
         * Collect entries that were still getting written before the
         * synchronize.
         */
        on_each_cpu(collect_tscs, cpu_tsc, 1);

        for (i = next; i < MCE_LOG_LEN; i++) {
                if (mcelog.entry[i].finished &&
                    mcelog.entry[i].tsc < cpu_tsc[mcelog.entry[i].cpu]) {
                        err |= copy_to_user(buf, mcelog.entry+i,
                                            sizeof(struct mce));
                        smp_rmb();
                        buf += sizeof(struct mce);
                        memset(&mcelog.entry[i], 0, sizeof(struct mce));
                }
        }
        mutex_unlock(&mce_read_mutex);
        kfree(cpu_tsc);

        return err ? -EFAULT : buf - ubuf;
}

static unsigned int mce_poll(struct file *file, poll_table *wait)
{
        poll_wait(file, &mce_wait, wait);
        if (rcu_dereference(mcelog.next))
                return POLLIN | POLLRDNORM;
        return 0;
}

static long mce_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
{
        int __user *p = (int __user *)arg;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        switch (cmd) {
        case MCE_GET_RECORD_LEN:
                return put_user(sizeof(struct mce), p);
        case MCE_GET_LOG_LEN:
                return put_user(MCE_LOG_LEN, p);
        case MCE_GETCLEAR_FLAGS: {
                unsigned flags;

                do {
                        flags = mcelog.flags;
                } while (cmpxchg(&mcelog.flags, flags, 0) != flags);

                return put_user(flags, p);
        }
        default:
                return -ENOTTY;
        }
}

/* Modified in mce-inject.c, so not static or const */
struct file_operations mce_chrdev_ops = {
        .open                   = mce_open,
        .release                = mce_release,
        .read                   = mce_read,
        .poll                   = mce_poll,
        .unlocked_ioctl         = mce_ioctl,
};
EXPORT_SYMBOL_GPL(mce_chrdev_ops);

static struct miscdevice mce_log_device = {
        MISC_MCELOG_MINOR,
        "mcelog",
        &mce_chrdev_ops,
};

/*
 * mce=off disables machine check
 * mce=TOLERANCELEVEL (number, see above)
 * mce=bootlog Log MCEs from before booting. Disabled by default on AMD.
 * mce=nobootlog Don't log MCEs from before booting.
 */
static int __init mcheck_enable(char *str)
{
        if (*str == 0)
                enable_p5_mce();
        if (*str == '=')
                str++;
        if (!strcmp(str, "off"))
                mce_disabled = 1;
        else if (!strcmp(str, "bootlog") || !strcmp(str, "nobootlog"))
                mce_bootlog = (str[0] == 'b');
        else if (isdigit(str[0]))
                get_option(&str, &tolerant);
        else {
                printk(KERN_INFO "mce argument %s ignored. Please use /sys\n",
                       str);
                return 0;
        }
        return 1;
}
__setup("mce", mcheck_enable);

/*
 * Sysfs support
 */

/*
 * Disable machine checks on suspend and shutdown. We can't really handle
 * them later.
 */
static int mce_disable(void)
{
        int i;

        for (i = 0; i < banks; i++) {
                if (!skip_bank_init(i))
                        wrmsrl(MSR_IA32_MC0_CTL + i*4, 0);
        }
        return 0;
}

static int mce_suspend(struct sys_device *dev, pm_message_t state)
{
        return mce_disable();
}

static int mce_shutdown(struct sys_device *dev)
{
        return mce_disable();
}

/*
 * On resume clear all MCE state. Don't want to see leftovers from the BIOS.
 * Only one CPU is active at this time, the others get re-added later using
 * CPU hotplug:
 */
static int mce_resume(struct sys_device *dev)
{
        mce_init();
        mce_cpu_features(&current_cpu_data);

        return 0;
}

static void mce_cpu_restart(void *data)
{
        del_timer_sync(&__get_cpu_var(mce_timer));
        if (mce_available(&current_cpu_data))
                mce_init();
        mce_init_timer();
}

/* Reinit MCEs after user configuration changes */
static void mce_restart(void)
{
        on_each_cpu(mce_cpu_restart, NULL, 1);
}

static struct sysdev_class mce_sysclass = {
        .suspend        = mce_suspend,
        .shutdown       = mce_shutdown,
        .resume         = mce_resume,
        .name           = "machinecheck",
};

DEFINE_PER_CPU(struct sys_device, mce_dev);

__cpuinitdata
void (*threshold_cpu_callback)(unsigned long action, unsigned int cpu);

static struct sysdev_attribute *bank_attrs;

static ssize_t show_bank(struct sys_device *s, struct sysdev_attribute *attr,
                         char *buf)
{
        u64 b = bank[attr - bank_attrs];

        return sprintf(buf, "%llx\n", b);
}

static ssize_t set_bank(struct sys_device *s, struct sysdev_attribute *attr,
                        const char *buf, size_t size)
{
        u64 new;

        if (strict_strtoull(buf, 0, &new) < 0)
                return -EINVAL;

        bank[attr - bank_attrs] = new;
        mce_restart();

        return size;
}

static ssize_t
show_trigger(struct sys_device *s, struct sysdev_attribute *attr, char *buf)
{
        strcpy(buf, trigger);
        strcat(buf, "\n");
        return strlen(trigger) + 1;
}

static ssize_t set_trigger(struct sys_device *s, struct sysdev_attribute *attr,
                                const char *buf, size_t siz)
{
        char *p;
        int len;

        strncpy(trigger, buf, sizeof(trigger));
        trigger[sizeof(trigger)-1] = 0;
        len = strlen(trigger);
        p = strchr(trigger, '\n');

        if (*p)
                *p = 0;

        return len;
}

static ssize_t store_int_with_restart(struct sys_device *s,
                                      struct sysdev_attribute *attr,
                                      const char *buf, size_t size)
{
        ssize_t ret = sysdev_store_int(s, attr, buf, size);
        mce_restart();
        return ret;
}

static SYSDEV_ATTR(trigger, 0644, show_trigger, set_trigger);
static SYSDEV_INT_ATTR(tolerant, 0644, tolerant);

static struct sysdev_ext_attribute attr_check_interval = {
        _SYSDEV_ATTR(check_interval, 0644, sysdev_show_int,
                     store_int_with_restart),
        &check_interval
};

static struct sysdev_attribute *mce_attrs[] = {
        &attr_tolerant.attr, &attr_check_interval.attr, &attr_trigger,
        NULL
};

static cpumask_var_t mce_dev_initialized;

/* Per cpu sysdev init. All of the cpus still share the same ctrl bank: */
static __cpuinit int mce_create_device(unsigned int cpu)
{
        int err;
        int i;

        if (!mce_available(&boot_cpu_data))
                return -EIO;

        memset(&per_cpu(mce_dev, cpu).kobj, 0, sizeof(struct kobject));
        per_cpu(mce_dev, cpu).id        = cpu;
        per_cpu(mce_dev, cpu).cls       = &mce_sysclass;

        err = sysdev_register(&per_cpu(mce_dev, cpu));
        if (err)
                return err;

        for (i = 0; mce_attrs[i]; i++) {
                err = sysdev_create_file(&per_cpu(mce_dev, cpu), mce_attrs[i]);
                if (err)
                        goto error;
        }
        for (i = 0; i < banks; i++) {
                err = sysdev_create_file(&per_cpu(mce_dev, cpu),
                                        &bank_attrs[i]);
                if (err)
                        goto error2;
        }
        cpumask_set_cpu(cpu, mce_dev_initialized);

        return 0;
error2:
        while (--i >= 0)
                sysdev_remove_file(&per_cpu(mce_dev, cpu), &bank_attrs[i]);
error:
        while (--i >= 0)
                sysdev_remove_file(&per_cpu(mce_dev, cpu), mce_attrs[i]);

        sysdev_unregister(&per_cpu(mce_dev, cpu));

        return err;
}

static __cpuinit void mce_remove_device(unsigned int cpu)
{
        int i;

        if (!cpumask_test_cpu(cpu, mce_dev_initialized))
                return;

        for (i = 0; mce_attrs[i]; i++)
                sysdev_remove_file(&per_cpu(mce_dev, cpu), mce_attrs[i]);

        for (i = 0; i < banks; i++)
                sysdev_remove_file(&per_cpu(mce_dev, cpu), &bank_attrs[i]);

        sysdev_unregister(&per_cpu(mce_dev, cpu));
        cpumask_clear_cpu(cpu, mce_dev_initialized);
}

/* Make sure there are no machine checks on offlined CPUs. */
static void mce_disable_cpu(void *h)
{
        unsigned long action = *(unsigned long *)h;
        int i;

        if (!mce_available(&current_cpu_data))
                return;
        if (!(action & CPU_TASKS_FROZEN))
                cmci_clear();
        for (i = 0; i < banks; i++) {
                if (!skip_bank_init(i))
                        wrmsrl(MSR_IA32_MC0_CTL + i*4, 0);
        }
}

static void mce_reenable_cpu(void *h)
{
        unsigned long action = *(unsigned long *)h;
        int i;

        if (!mce_available(&current_cpu_data))
                return;

        if (!(action & CPU_TASKS_FROZEN))
                cmci_reenable();
        for (i = 0; i < banks; i++) {
                if (!skip_bank_init(i))
                        wrmsrl(MSR_IA32_MC0_CTL + i*4, bank[i]);
        }
}

/* Get notified when a cpu comes on/off. Be hotplug friendly. */
static int __cpuinit
mce_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
        unsigned int cpu = (unsigned long)hcpu;
        struct timer_list *t = &per_cpu(mce_timer, cpu);

        switch (action) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                mce_create_device(cpu);
                if (threshold_cpu_callback)
                        threshold_cpu_callback(action, cpu);
                break;
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                if (threshold_cpu_callback)
                        threshold_cpu_callback(action, cpu);
                mce_remove_device(cpu);
                break;
        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
                del_timer_sync(t);
                smp_call_function_single(cpu, mce_disable_cpu, &action, 1);
                break;
        case CPU_DOWN_FAILED:
        case CPU_DOWN_FAILED_FROZEN:
                t->expires = round_jiffies(jiffies +
                                                __get_cpu_var(next_interval));
                add_timer_on(t, cpu);
                smp_call_function_single(cpu, mce_reenable_cpu, &action, 1);
                break;
        case CPU_POST_DEAD:
                /* intentionally ignoring frozen here */
                cmci_rediscover(cpu);
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block mce_cpu_notifier __cpuinitdata = {
        .notifier_call = mce_cpu_callback,
};

static __init int mce_init_banks(void)
{
        int i;

        bank_attrs = kzalloc(sizeof(struct sysdev_attribute) * banks,
                                GFP_KERNEL);
        if (!bank_attrs)
                return -ENOMEM;

        for (i = 0; i < banks; i++) {
                struct sysdev_attribute *a = &bank_attrs[i];

                a->attr.name    = kasprintf(GFP_KERNEL, "bank%d", i);
                if (!a->attr.name)
                        goto nomem;

                a->attr.mode    = 0644;
                a->show         = show_bank;
                a->store        = set_bank;
        }
        return 0;

nomem:
        while (--i >= 0)
                kfree(bank_attrs[i].attr.name);
        kfree(bank_attrs);
        bank_attrs = NULL;

        return -ENOMEM;
}

static __init int mce_init_device(void)
{
        int err;
        int i = 0;

        if (!mce_available(&boot_cpu_data))
                return -EIO;

        alloc_cpumask_var(&mce_dev_initialized, GFP_KERNEL);

        err = mce_init_banks();
        if (err)
                return err;

        err = sysdev_class_register(&mce_sysclass);
        if (err)
                return err;

        for_each_online_cpu(i) {
                err = mce_create_device(i);
                if (err)
                        return err;
        }

        register_hotcpu_notifier(&mce_cpu_notifier);
        misc_register(&mce_log_device);

        return err;
}

device_initcall(mce_init_device);

#else /* CONFIG_X86_OLD_MCE: */

int nr_mce_banks;
EXPORT_SYMBOL_GPL(nr_mce_banks);        /* non-fatal.o */

/* This has to be run for each processor */
void mcheck_init(struct cpuinfo_x86 *c)
{
        if (mce_disabled == 1)
                return;

        switch (c->x86_vendor) {
        case X86_VENDOR_AMD:
                amd_mcheck_init(c);
                break;

        case X86_VENDOR_INTEL:
                if (c->x86 == 5)
                        intel_p5_mcheck_init(c);
                if (c->x86 == 6)
                        intel_p6_mcheck_init(c);
                if (c->x86 == 15)
                        intel_p4_mcheck_init(c);
                break;

        case X86_VENDOR_CENTAUR:
                if (c->x86 == 5)
                        winchip_mcheck_init(c);
                break;

        default:
                break;
        }
        printk(KERN_INFO "mce: CPU supports %d MCE banks\n", nr_mce_banks);
}

static int __init mcheck_enable(char *str)
{
        mce_disabled = -1;
        return 1;
}

__setup("mce", mcheck_enable);

#endif /* CONFIG_X86_OLD_MCE */

/*
 * Old style boot options parsing. Only for compatibility.
 */
static int __init mcheck_disable(char *str)
{
        mce_disabled = 1;
        return 1;
}
__setup("nomce", mcheck_disable);