Merge tag 'x86-mce-merge' of git://git.kernel.org/pub/scm/linux/kernel/git/ras/ras

[firefly-linux-kernel-4.4.55.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/device.h>
#include <linux/syscore_ops.h>
#include <linux/delay.h>
#include <linux/ctype.h>
#include <linux/sched.h>
#include <linux/sysfs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/kmod.h>
#include <linux/poll.h>
#include <linux/nmi.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/debugfs.h>
#include <linux/irq_work.h>
#include <linux/export.h>

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

#include "mce-internal.h"

static DEFINE_MUTEX(mce_chrdev_read_mutex);

#define rcu_dereference_check_mce(p) \
        rcu_dereference_index_check((p), \
                              rcu_read_lock_sched_held() || \
                              lockdep_is_held(&mce_chrdev_read_mutex))

#define CREATE_TRACE_POINTS
#include <trace/events/mce.h>

int mce_disabled __read_mostly;

#define MISC_MCELOG_MINOR       227

#define SPINUNIT 100    /* 100ns */

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                __read_mostly = 1;
static int                      banks                   __read_mostly;
static int                      rip_msr                 __read_mostly;
static int                      mce_bootlog             __read_mostly = -1;
static int                      monarch_timeout         __read_mostly = -1;
static int                      mce_panic_timeout       __read_mostly;
static int                      mce_dont_log_ce         __read_mostly;
int                             mce_cmci_disabled       __read_mostly;
int                             mce_ignore_ce           __read_mostly;
int                             mce_ser                 __read_mostly;

struct mce_bank                *mce_banks               __read_mostly;

/* User mode helper program triggered by machine check event */
static unsigned long            mce_need_notify;
static char                     mce_helper[128];
static char                     *mce_helper_argv[2] = { mce_helper, NULL };

static DECLARE_WAIT_QUEUE_HEAD(mce_chrdev_wait);

static DEFINE_PER_CPU(struct mce, mces_seen);
static int                      cpu_missing;

/* 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 DEFINE_PER_CPU(struct work_struct, mce_work);

/*
 * CPU/chipset specific EDAC code can register a notifier call here to print
 * MCE errors in a human-readable form.
 */
ATOMIC_NOTIFIER_HEAD(x86_mce_decoder_chain);

/* Do initial initialization of a struct mce */
void mce_setup(struct mce *m)
{
        memset(m, 0, sizeof(struct mce));
        m->cpu = m->extcpu = smp_processor_id();
        rdtscll(m->tsc);
        /* We hope get_seconds stays lockless */
        m->time = get_seconds();
        m->cpuvendor = boot_cpu_data.x86_vendor;
        m->cpuid = cpuid_eax(1);
        m->socketid = cpu_data(m->extcpu).phys_proc_id;
        m->apicid = cpu_data(m->extcpu).initial_apicid;
        rdmsrl(MSR_IA32_MCG_CAP, m->mcgcap);
}

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 = {
        .signature      = MCE_LOG_SIGNATURE,
        .len            = MCE_LOG_LEN,
        .recordlen      = sizeof(struct mce),
};

void mce_log(struct mce *mce)
{
        unsigned next, entry;
        int ret = 0;

        /* Emit the trace record: */
        trace_mce_record(mce);

        ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce);
        if (ret == NOTIFY_STOP)
                return;

        mce->finished = 0;
        wmb();
        for (;;) {
                entry = rcu_dereference_check_mce(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();

        mce->finished = 1;
        set_bit(0, &mce_need_notify);
}

static void drain_mcelog_buffer(void)
{
        unsigned int next, i, prev = 0;

        next = ACCESS_ONCE(mcelog.next);

        do {
                struct mce *m;

                /* drain what was logged during boot */
                for (i = prev; i < next; i++) {
                        unsigned long start = jiffies;
                        unsigned retries = 1;

                        m = &mcelog.entry[i];

                        while (!m->finished) {
                                if (time_after_eq(jiffies, start + 2*retries))
                                        retries++;

                                cpu_relax();

                                if (!m->finished && retries >= 4) {
                                        pr_err("MCE: skipping error being logged currently!\n");
                                        break;
                                }
                        }
                        smp_rmb();
                        atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
                }

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


void mce_register_decode_chain(struct notifier_block *nb)
{
        atomic_notifier_chain_register(&x86_mce_decoder_chain, nb);
        drain_mcelog_buffer();
}
EXPORT_SYMBOL_GPL(mce_register_decode_chain);

void mce_unregister_decode_chain(struct notifier_block *nb)
{
        atomic_notifier_chain_unregister(&x86_mce_decoder_chain, nb);
}
EXPORT_SYMBOL_GPL(mce_unregister_decode_chain);

static void print_mce(struct mce *m)
{
        int ret = 0;

        pr_emerg(HW_ERR "CPU %d: Machine Check Exception: %Lx Bank %d: %016Lx\n",
               m->extcpu, m->mcgstatus, m->bank, m->status);

        if (m->ip) {
                pr_emerg(HW_ERR "RIP%s %02x:<%016Lx> ",
                        !(m->mcgstatus & MCG_STATUS_EIPV) ? " !INEXACT!" : "",
                                m->cs, m->ip);

                if (m->cs == __KERNEL_CS)
                        print_symbol("{%s}", m->ip);
                pr_cont("\n");
        }

        pr_emerg(HW_ERR "TSC %llx ", m->tsc);
        if (m->addr)
                pr_cont("ADDR %llx ", m->addr);
        if (m->misc)
                pr_cont("MISC %llx ", m->misc);

        pr_cont("\n");
        /*
         * Note this output is parsed by external tools and old fields
         * should not be changed.
         */
        pr_emerg(HW_ERR "PROCESSOR %u:%x TIME %llu SOCKET %u APIC %x microcode %x\n",
                m->cpuvendor, m->cpuid, m->time, m->socketid, m->apicid,
                cpu_data(m->extcpu).microcode);

        /*
         * Print out human-readable details about the MCE error,
         * (if the CPU has an implementation for that)
         */
        ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
        if (ret == NOTIFY_STOP)
                return;

        pr_emerg_ratelimited(HW_ERR "Run the above through 'mcelog --ascii'\n");
}

#define PANIC_TIMEOUT 5 /* 5 seconds */

static atomic_t mce_paniced;

static int fake_panic;
static atomic_t mce_fake_paniced;

/* Panic in progress. Enable interrupts and wait for final IPI */
static void wait_for_panic(void)
{
        long timeout = PANIC_TIMEOUT*USEC_PER_SEC;

        preempt_disable();
        local_irq_enable();
        while (timeout-- > 0)
                udelay(1);
        if (panic_timeout == 0)
                panic_timeout = mce_panic_timeout;
        panic("Panicing machine check CPU died");
}

static void mce_panic(char *msg, struct mce *final, char *exp)
{
        int i, apei_err = 0;

        if (!fake_panic) {
                /*
                 * Make sure only one CPU runs in machine check panic
                 */
                if (atomic_inc_return(&mce_paniced) > 1)
                        wait_for_panic();
                barrier();

                bust_spinlocks(1);
                console_verbose();
        } else {
                /* Don't log too much for fake panic */
                if (atomic_inc_return(&mce_fake_paniced) > 1)
                        return;
        }
        /* First print corrected ones that are still unlogged */
        for (i = 0; i < MCE_LOG_LEN; i++) {
                struct mce *m = &mcelog.entry[i];
                if (!(m->status & MCI_STATUS_VAL))
                        continue;
                if (!(m->status & MCI_STATUS_UC)) {
                        print_mce(m);
                        if (!apei_err)
                                apei_err = apei_write_mce(m);
                }
        }
        /* Now print uncorrected but with the final one last */
        for (i = 0; i < MCE_LOG_LEN; i++) {
                struct mce *m = &mcelog.entry[i];
                if (!(m->status & MCI_STATUS_VAL))
                        continue;
                if (!(m->status & MCI_STATUS_UC))
                        continue;
                if (!final || memcmp(m, final, sizeof(struct mce))) {
                        print_mce(m);
                        if (!apei_err)
                                apei_err = apei_write_mce(m);
                }
        }
        if (final) {
                print_mce(final);
                if (!apei_err)
                        apei_err = apei_write_mce(final);
        }
        if (cpu_missing)
                pr_emerg(HW_ERR "Some CPUs didn't answer in synchronization\n");
        if (exp)
                pr_emerg(HW_ERR "Machine check: %s\n", exp);
        if (!fake_panic) {
                if (panic_timeout == 0)
                        panic_timeout = mce_panic_timeout;
                panic(msg);
        } else
                pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);
}

/* Support code for software error injection */

static int msr_to_offset(u32 msr)
{
        unsigned bank = __this_cpu_read(injectm.bank);

        if (msr == rip_msr)
                return offsetof(struct mce, ip);
        if (msr == MSR_IA32_MCx_STATUS(bank))
                return offsetof(struct mce, status);
        if (msr == MSR_IA32_MCx_ADDR(bank))
                return offsetof(struct mce, addr);
        if (msr == MSR_IA32_MCx_MISC(bank))
                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 (__this_cpu_read(injectm.finished)) {
                int offset = msr_to_offset(msr);

                if (offset < 0)
                        return 0;
                return *(u64 *)((char *)&__get_cpu_var(injectm) + offset);
        }

        if (rdmsrl_safe(msr, &v)) {
                WARN_ONCE(1, "mce: Unable to read msr %d!\n", msr);
                /*
                 * Return zero in case the access faulted. This should
                 * not happen normally but can happen if the CPU does
                 * something weird, or if the code is buggy.
                 */
                v = 0;
        }

        return v;
}

static void mce_wrmsrl(u32 msr, u64 v)
{
        if (__this_cpu_read(injectm.finished)) {
                int offset = msr_to_offset(msr);

                if (offset >= 0)
                        *(u64 *)((char *)&__get_cpu_var(injectm) + offset) = v;
                return;
        }
        wrmsrl(msr, v);
}

/*
 * Collect all global (w.r.t. this processor) status about this machine
 * check into our "mce" struct so that we can use it later to assess
 * the severity of the problem as we read per-bank specific details.
 */
static inline void mce_gather_info(struct mce *m, struct pt_regs *regs)
{
        mce_setup(m);

        m->mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
        if (regs) {
                /*
                 * Get the address of the instruction at the time of
                 * the machine check error.
                 */
                if (m->mcgstatus & (MCG_STATUS_RIPV|MCG_STATUS_EIPV)) {
                        m->ip = regs->ip;
                        m->cs = regs->cs;

                        /*
                         * When in VM86 mode make the cs look like ring 3
                         * always. This is a lie, but it's better than passing
                         * the additional vm86 bit around everywhere.
                         */
                        if (v8086_mode(regs))
                                m->cs |= 3;
                }
                /* Use accurate RIP reporting if available. */
                if (rip_msr)
                        m->ip = mce_rdmsrl(rip_msr);
        }
}

/*
 * Simple lockless ring to communicate PFNs from the exception handler with the
 * process context work function. This is vastly simplified because there's
 * only a single reader and a single writer.
 */
#define MCE_RING_SIZE 16        /* we use one entry less */

struct mce_ring {
        unsigned short start;
        unsigned short end;
        unsigned long ring[MCE_RING_SIZE];
};
static DEFINE_PER_CPU(struct mce_ring, mce_ring);

/* Runs with CPU affinity in workqueue */
static int mce_ring_empty(void)
{
        struct mce_ring *r = &__get_cpu_var(mce_ring);

        return r->start == r->end;
}

static int mce_ring_get(unsigned long *pfn)
{
        struct mce_ring *r;
        int ret = 0;

        *pfn = 0;
        get_cpu();
        r = &__get_cpu_var(mce_ring);
        if (r->start == r->end)
                goto out;
        *pfn = r->ring[r->start];
        r->start = (r->start + 1) % MCE_RING_SIZE;
        ret = 1;
out:
        put_cpu();
        return ret;
}

/* Always runs in MCE context with preempt off */
static int mce_ring_add(unsigned long pfn)
{
        struct mce_ring *r = &__get_cpu_var(mce_ring);
        unsigned next;

        next = (r->end + 1) % MCE_RING_SIZE;
        if (next == r->start)
                return -1;
        r->ring[r->end] = pfn;
        wmb();
        r->end = next;
        return 0;
}

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 void mce_schedule_work(void)
{
        if (!mce_ring_empty()) {
                struct work_struct *work = &__get_cpu_var(mce_work);
                if (!work_pending(work))
                        schedule_work(work);
        }
}

DEFINE_PER_CPU(struct irq_work, mce_irq_work);

static void mce_irq_work_cb(struct irq_work *entry)
{
        mce_notify_irq();
        mce_schedule_work();
}

static void mce_report_event(struct pt_regs *regs)
{
        if (regs->flags & (X86_VM_MASK|X86_EFLAGS_IF)) {
                mce_notify_irq();
                /*
                 * Triggering the work queue here is just an insurance
                 * policy in case the syscall exit notify handler
                 * doesn't run soon enough or ends up running on the
                 * wrong CPU (can happen when audit sleeps)
                 */
                mce_schedule_work();
                return;
        }

        irq_work_queue(&__get_cpu_var(mce_irq_work));
}

/*
 * Read ADDR and MISC registers.
 */
static void mce_read_aux(struct mce *m, int i)
{
        if (m->status & MCI_STATUS_MISCV)
                m->misc = mce_rdmsrl(MSR_IA32_MCx_MISC(i));
        if (m->status & MCI_STATUS_ADDRV) {
                m->addr = mce_rdmsrl(MSR_IA32_MCx_ADDR(i));

                /*
                 * Mask the reported address by the reported granularity.
                 */
                if (mce_ser && (m->status & MCI_STATUS_MISCV)) {
                        u8 shift = MCI_MISC_ADDR_LSB(m->misc);
                        m->addr >>= shift;
                        m->addr <<= shift;
                }
        }
}

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.
 *
 * Note: spec recommends to panic for fatal unsignalled
 * errors here. However this would be quite problematic --
 * we would need to reimplement the Monarch handling and
 * it would mess up the exclusion between exception handler
 * and poll hander -- * so we skip this for now.
 * These cases should not happen anyways, or only when the CPU
 * is already totally * confused. In this case it's likely it will
 * not fully execute the machine check handler either.
 */
void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
{
        struct mce m;
        int i;

        this_cpu_inc(mce_poll_count);

        mce_gather_info(&m, NULL);

        for (i = 0; i < banks; i++) {
                if (!mce_banks[i].ctl || !test_bit(i, *b))
                        continue;

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

                barrier();
                m.status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
                if (!(m.status & MCI_STATUS_VAL))
                        continue;

                /*
                 * Uncorrected or signalled events are handled by the exception
                 * handler when it is enabled, so don't process those here.
                 *
                 * TBD do the same check for MCI_STATUS_EN here?
                 */
                if (!(flags & MCP_UC) &&
                    (m.status & (mce_ser ? MCI_STATUS_S : MCI_STATUS_UC)))
                        continue;

                mce_read_aux(&m, i);

                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_dont_log_ce)
                        mce_log(&m);

                /*
                 * Clear state for this bank.
                 */
                mce_wrmsrl(MSR_IA32_MCx_STATUS(i), 0);
        }

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

        sync_core();
}
EXPORT_SYMBOL_GPL(machine_check_poll);

/*
 * Do a quick check if any of the events requires a panic.
 * This decides if we keep the events around or clear them.
 */
static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp)
{
        int i, ret = 0;

        for (i = 0; i < banks; i++) {
                m->status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
                if (m->status & MCI_STATUS_VAL)
                        __set_bit(i, validp);
                if (mce_severity(m, tolerant, msg) >= MCE_PANIC_SEVERITY)
                        ret = 1;
        }
        return ret;
}

/*
 * Variable to establish order between CPUs while scanning.
 * Each CPU spins initially until executing is equal its number.
 */
static atomic_t mce_executing;

/*
 * Defines order of CPUs on entry. First CPU becomes Monarch.
 */
static atomic_t mce_callin;

/*
 * Check if a timeout waiting for other CPUs happened.
 */
static int mce_timed_out(u64 *t)
{
        /*
         * The others already did panic for some reason.
         * Bail out like in a timeout.
         * rmb() to tell the compiler that system_state
         * might have been modified by someone else.
         */
        rmb();
        if (atomic_read(&mce_paniced))
                wait_for_panic();
        if (!monarch_timeout)
                goto out;
        if ((s64)*t < SPINUNIT) {
                /* CHECKME: Make panic default for 1 too? */
                if (tolerant < 1)
                        mce_panic("Timeout synchronizing machine check over CPUs",
                                  NULL, NULL);
                cpu_missing = 1;
                return 1;
        }
        *t -= SPINUNIT;
out:
        touch_nmi_watchdog();
        return 0;
}

/*
 * The Monarch's reign.  The Monarch is the CPU who entered
 * the machine check handler first. It waits for the others to
 * raise the exception too and then grades them. When any
 * error is fatal panic. Only then let the others continue.
 *
 * The other CPUs entering the MCE handler will be controlled by the
 * Monarch. They are called Subjects.
 *
 * This way we prevent any potential data corruption in a unrecoverable case
 * and also makes sure always all CPU's errors are examined.
 *
 * Also this detects the case of a machine check event coming from outer
 * space (not detected by any CPUs) In this case some external agent wants
 * us to shut down, so panic too.
 *
 * The other CPUs might still decide to panic if the handler happens
 * in a unrecoverable place, but in this case the system is in a semi-stable
 * state and won't corrupt anything by itself. It's ok to let the others
 * continue for a bit first.
 *
 * All the spin loops have timeouts; when a timeout happens a CPU
 * typically elects itself to be Monarch.
 */
static void mce_reign(void)
{
        int cpu;
        struct mce *m = NULL;
        int global_worst = 0;
        char *msg = NULL;
        char *nmsg = NULL;

        /*
         * This CPU is the Monarch and the other CPUs have run
         * through their handlers.
         * Grade the severity of the errors of all the CPUs.
         */
        for_each_possible_cpu(cpu) {
                int severity = mce_severity(&per_cpu(mces_seen, cpu), tolerant,
                                            &nmsg);
                if (severity > global_worst) {
                        msg = nmsg;
                        global_worst = severity;
                        m = &per_cpu(mces_seen, cpu);
                }
        }

        /*
         * Cannot recover? Panic here then.
         * This dumps all the mces in the log buffer and stops the
         * other CPUs.
         */
        if (m && global_worst >= MCE_PANIC_SEVERITY && tolerant < 3)
                mce_panic("Fatal Machine check", m, msg);

        /*
         * For UC somewhere we let the CPU who detects it handle it.
         * Also must let continue the others, otherwise the handling
         * CPU could deadlock on a lock.
         */

        /*
         * No machine check event found. Must be some external
         * source or one CPU is hung. Panic.
         */
        if (global_worst <= MCE_KEEP_SEVERITY && tolerant < 3)
                mce_panic("Machine check from unknown source", NULL, NULL);

        /*
         * Now clear all the mces_seen so that they don't reappear on
         * the next mce.
         */
        for_each_possible_cpu(cpu)
                memset(&per_cpu(mces_seen, cpu), 0, sizeof(struct mce));
}

static atomic_t global_nwo;

/*
 * Start of Monarch synchronization. This waits until all CPUs have
 * entered the exception handler and then determines if any of them
 * saw a fatal event that requires panic. Then it executes them
 * in the entry order.
 * TBD double check parallel CPU hotunplug
 */
static int mce_start(int *no_way_out)
{
        int order;
        int cpus = num_online_cpus();
        u64 timeout = (u64)monarch_timeout * NSEC_PER_USEC;

        if (!timeout)
                return -1;

        atomic_add(*no_way_out, &global_nwo);
        /*
         * global_nwo should be updated before mce_callin
         */
        smp_wmb();
        order = atomic_inc_return(&mce_callin);

        /*
         * Wait for everyone.
         */
        while (atomic_read(&mce_callin) != cpus) {
                if (mce_timed_out(&timeout)) {
                        atomic_set(&global_nwo, 0);
                        return -1;
                }
                ndelay(SPINUNIT);
        }

        /*
         * mce_callin should be read before global_nwo
         */
        smp_rmb();

        if (order == 1) {
                /*
                 * Monarch: Starts executing now, the others wait.
                 */
                atomic_set(&mce_executing, 1);
        } else {
                /*
                 * Subject: Now start the scanning loop one by one in
                 * the original callin order.
                 * This way when there are any shared banks it will be
                 * only seen by one CPU before cleared, avoiding duplicates.
                 */
                while (atomic_read(&mce_executing) < order) {
                        if (mce_timed_out(&timeout)) {
                                atomic_set(&global_nwo, 0);
                                return -1;
                        }
                        ndelay(SPINUNIT);
                }
        }

        /*
         * Cache the global no_way_out state.
         */
        *no_way_out = atomic_read(&global_nwo);

        return order;
}

/*
 * Synchronize between CPUs after main scanning loop.
 * This invokes the bulk of the Monarch processing.
 */
static int mce_end(int order)
{
        int ret = -1;
        u64 timeout = (u64)monarch_timeout * NSEC_PER_USEC;

        if (!timeout)
                goto reset;
        if (order < 0)
                goto reset;

        /*
         * Allow others to run.
         */
        atomic_inc(&mce_executing);

        if (order == 1) {
                /* CHECKME: Can this race with a parallel hotplug? */
                int cpus = num_online_cpus();

                /*
                 * Monarch: Wait for everyone to go through their scanning
                 * loops.
                 */
                while (atomic_read(&mce_executing) <= cpus) {
                        if (mce_timed_out(&timeout))
                                goto reset;
                        ndelay(SPINUNIT);
                }

                mce_reign();
                barrier();
                ret = 0;
        } else {
                /*
                 * Subject: Wait for Monarch to finish.
                 */
                while (atomic_read(&mce_executing) != 0) {
                        if (mce_timed_out(&timeout))
                                goto reset;
                        ndelay(SPINUNIT);
                }

                /*
                 * Don't reset anything. That's done by the Monarch.
                 */
                return 0;
        }

        /*
         * Reset all global state.
         */
reset:
        atomic_set(&global_nwo, 0);
        atomic_set(&mce_callin, 0);
        barrier();

        /*
         * Let others run again.
         */
        atomic_set(&mce_executing, 0);
        return ret;
}

/*
 * Check if the address reported by the CPU is in a format we can parse.
 * It would be possible to add code for most other cases, but all would
 * be somewhat complicated (e.g. segment offset would require an instruction
 * parser). So only support physical addresses up to page granuality for now.
 */
static int mce_usable_address(struct mce *m)
{
        if (!(m->status & MCI_STATUS_MISCV) || !(m->status & MCI_STATUS_ADDRV))
                return 0;
        if (MCI_MISC_ADDR_LSB(m->misc) > PAGE_SHIFT)
                return 0;
        if (MCI_MISC_ADDR_MODE(m->misc) != MCI_MISC_ADDR_PHYS)
                return 0;
        return 1;
}

static void mce_clear_state(unsigned long *toclear)
{
        int i;

        for (i = 0; i < banks; i++) {
                if (test_bit(i, toclear))
                        mce_wrmsrl(MSR_IA32_MCx_STATUS(i), 0);
        }
}

/*
 * Need to save faulting physical address associated with a process
 * in the machine check handler some place where we can grab it back
 * later in mce_notify_process()
 */
#define MCE_INFO_MAX    16

struct mce_info {
        atomic_t                inuse;
        struct task_struct      *t;
        __u64                   paddr;
        int                     restartable;
} mce_info[MCE_INFO_MAX];

static void mce_save_info(__u64 addr, int c)
{
        struct mce_info *mi;

        for (mi = mce_info; mi < &mce_info[MCE_INFO_MAX]; mi++) {
                if (atomic_cmpxchg(&mi->inuse, 0, 1) == 0) {
                        mi->t = current;
                        mi->paddr = addr;
                        mi->restartable = c;
                        return;
                }
        }

        mce_panic("Too many concurrent recoverable errors", NULL, NULL);
}

static struct mce_info *mce_find_info(void)
{
        struct mce_info *mi;

        for (mi = mce_info; mi < &mce_info[MCE_INFO_MAX]; mi++)
                if (atomic_read(&mi->inuse) && mi->t == current)
                        return mi;
        return NULL;
}

static void mce_clear_info(struct mce_info *mi)
{
        atomic_set(&mi->inuse, 0);
}

/*
 * 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!
 *
 * On Intel systems this is entered on all CPUs in parallel through
 * MCE broadcast. However some CPUs might be broken beyond repair,
 * so be always careful when synchronizing with others.
 */
void do_machine_check(struct pt_regs *regs, long error_code)
{
        struct mce m, *final;
        int i;
        int worst = 0;
        int severity;
        /*
         * Establish sequential order between the CPUs entering the machine
         * check handler.
         */
        int order;
        /*
         * 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);
        DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
        char *msg = "Unknown";

        atomic_inc(&mce_entry);

        this_cpu_inc(mce_exception_count);

        if (!banks)
                goto out;

        mce_gather_info(&m, regs);

        final = &__get_cpu_var(mces_seen);
        *final = m;

        memset(valid_banks, 0, sizeof(valid_banks));
        no_way_out = mce_no_way_out(&m, &msg, valid_banks);

        barrier();

        /*
         * When no restart IP might need to kill or panic.
         * Assume the worst for now, but if we find the
         * severity is MCE_AR_SEVERITY we have other options.
         */
        if (!(m.mcgstatus & MCG_STATUS_RIPV))
                kill_it = 1;

        /*
         * Go through all the banks in exclusion of the other CPUs.
         * This way we don't report duplicated events on shared banks
         * because the first one to see it will clear it.
         */
        order = mce_start(&no_way_out);
        for (i = 0; i < banks; i++) {
                __clear_bit(i, toclear);
                if (!test_bit(i, valid_banks))
                        continue;
                if (!mce_banks[i].ctl)
                        continue;

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

                m.status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
                if ((m.status & MCI_STATUS_VAL) == 0)
                        continue;

                /*
                 * Non uncorrected or non signaled errors are handled by
                 * machine_check_poll. Leave them alone, unless this panics.
                 */
                if (!(m.status & (mce_ser ? MCI_STATUS_S : MCI_STATUS_UC)) &&
                        !no_way_out)
                        continue;

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

                severity = mce_severity(&m, tolerant, NULL);

                /*
                 * When machine check was for corrected handler don't touch,
                 * unless we're panicing.
                 */
                if (severity == MCE_KEEP_SEVERITY && !no_way_out)
                        continue;
                __set_bit(i, toclear);
                if (severity == MCE_NO_SEVERITY) {
                        /*
                         * Machine check event was not enabled. Clear, but
                         * ignore.
                         */
                        continue;
                }

                mce_read_aux(&m, i);

                /*
                 * Action optional error. Queue address for later processing.
                 * When the ring overflows we just ignore the AO error.
                 * RED-PEN add some logging mechanism when
                 * usable_address or mce_add_ring fails.
                 * RED-PEN don't ignore overflow for tolerant == 0
                 */
                if (severity == MCE_AO_SEVERITY && mce_usable_address(&m))
                        mce_ring_add(m.addr >> PAGE_SHIFT);

                mce_log(&m);

                if (severity > worst) {
                        *final = m;
                        worst = severity;
                }
        }

        /* mce_clear_state will clear *final, save locally for use later */
        m = *final;

        if (!no_way_out)
                mce_clear_state(toclear);

        /*
         * Do most of the synchronization with other CPUs.
         * When there's any problem use only local no_way_out state.
         */
        if (mce_end(order) < 0)
                no_way_out = worst >= MCE_PANIC_SEVERITY;

        /*
         * At insane "tolerant" levels we take no action. Otherwise
         * we only die if we have no other choice. For less serious
         * issues we try to recover, or limit damage to the current
         * process.
         */
        if (tolerant < 3) {
                if (no_way_out)
                        mce_panic("Fatal machine check on current CPU", &m, msg);
                if (worst == MCE_AR_SEVERITY) {
                        /* schedule action before return to userland */
                        mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV);
                        set_thread_flag(TIF_MCE_NOTIFY);
                } else if (kill_it) {
                        force_sig(SIGBUS, current);
                }
        }

        if (worst > 0)
                mce_report_event(regs);
        mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
out:
        atomic_dec(&mce_entry);
        sync_core();
}
EXPORT_SYMBOL_GPL(do_machine_check);

#ifndef CONFIG_MEMORY_FAILURE
int memory_failure(unsigned long pfn, int vector, int flags)
{
        /* mce_severity() should not hand us an ACTION_REQUIRED error */
        BUG_ON(flags & MF_ACTION_REQUIRED);
        printk(KERN_ERR "Uncorrected memory error in page 0x%lx ignored\n"
                "Rebuild kernel with CONFIG_MEMORY_FAILURE=y for smarter handling\n", pfn);

        return 0;
}
#endif

/*
 * Called in process context that interrupted by MCE and marked with
 * TIF_MCE_NOTIFY, just before returning to erroneous userland.
 * This code is allowed to sleep.
 * Attempt possible recovery such as calling the high level VM handler to
 * process any corrupted pages, and kill/signal current process if required.
 * Action required errors are handled here.
 */
void mce_notify_process(void)
{
        unsigned long pfn;
        struct mce_info *mi = mce_find_info();

        if (!mi)
                mce_panic("Lost physical address for unconsumed uncorrectable error", NULL, NULL);
        pfn = mi->paddr >> PAGE_SHIFT;

        clear_thread_flag(TIF_MCE_NOTIFY);

        pr_err("Uncorrected hardware memory error in user-access at %llx",
                 mi->paddr);
        /*
         * We must call memory_failure() here even if the current process is
         * doomed. We still need to mark the page as poisoned and alert any
         * other users of the page.
         */
        if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0 ||
                           mi->restartable == 0) {
                pr_err("Memory error not recovered");
                force_sig(SIGBUS, current);
        }
        mce_clear_info(mi);
}

/*
 * Action optional processing happens here (picking up
 * from the list of faulting pages that do_machine_check()
 * placed into the "ring").
 */
static void mce_process_work(struct work_struct *dummy)
{
        unsigned long pfn;

        while (mce_ring_get(&pfn))
                memory_failure(pfn, MCE_VECTOR, 0);
}

#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, mce_next_interval); /* in jiffies */
static DEFINE_PER_CPU(struct timer_list, mce_timer);

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

        WARN_ON(smp_processor_id() != data);

        if (mce_available(__this_cpu_ptr(&cpu_info))) {
                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(mce_next_interval);
        if (mce_notify_irq())
                *n = max(*n/2, HZ/100);
        else
                *n = min(*n*2, (int)round_jiffies_relative(check_interval*HZ));

        t->expires = jiffies + *n;
        add_timer_on(t, smp_processor_id());
}

/* Must not be called in IRQ context where del_timer_sync() can deadlock */
static void mce_timer_delete_all(void)
{
        int cpu;

        for_each_online_cpu(cpu)
                del_timer_sync(&per_cpu(mce_timer, cpu));
}

static void mce_do_trigger(struct work_struct *work)
{
        call_usermodehelper(mce_helper, mce_helper_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_irq(void)
{
        /* Not more than two messages every minute */
        static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);

        if (test_and_clear_bit(0, &mce_need_notify)) {
                /* wake processes polling /dev/mcelog */
                wake_up_interruptible(&mce_chrdev_wait);

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

                if (__ratelimit(&ratelimit))
                        pr_info(HW_ERR "Machine check events logged\n");

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

static int __cpuinit __mcheck_cpu_mce_banks_init(void)
{
        int i;

        mce_banks = kzalloc(banks * sizeof(struct mce_bank), GFP_KERNEL);
        if (!mce_banks)
                return -ENOMEM;
        for (i = 0; i < banks; i++) {
                struct mce_bank *b = &mce_banks[i];

                b->ctl = -1ULL;
                b->init = 1;
        }
        return 0;
}

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

        rdmsrl(MSR_IA32_MCG_CAP, cap);

        b = cap & MCG_BANKCNT_MASK;
        if (!banks)
                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 (!mce_banks) {
                int err = __mcheck_cpu_mce_banks_init();

                if (err)
                        return err;
        }

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

        if (cap & MCG_SER_P)
                mce_ser = 1;

        return 0;
}

static void __mcheck_cpu_init_generic(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++) {
                struct mce_bank *b = &mce_banks[i];

                if (!b->init)
                        continue;
                wrmsrl(MSR_IA32_MCx_CTL(i), b->ctl);
                wrmsrl(MSR_IA32_MCx_STATUS(i), 0);
        }
}

/* Add per CPU specific workarounds here */
static int __cpuinit __mcheck_cpu_apply_quirks(struct cpuinfo_x86 *c)
{
        if (c->x86_vendor == X86_VENDOR_UNKNOWN) {
                pr_info("MCE: unknown CPU type - not enabling MCE support.\n");
                return -EOPNOTSUPP;
        }

        /* 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 *)&mce_banks[4].ctl);
                }
                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 && banks > 0)
                        mce_banks[0].ctl = 0;

                 /*
                  * Turn off MC4_MISC thresholding banks on those models since
                  * they're not supported there.
                  */
                 if (c->x86 == 0x15 &&
                     (c->x86_model >= 0x10 && c->x86_model <= 0x1f)) {
                         int i;
                         u64 val, hwcr;
                         bool need_toggle;
                         u32 msrs[] = {
                                0x00000413, /* MC4_MISC0 */
                                0xc0000408, /* MC4_MISC1 */
                         };

                         rdmsrl(MSR_K7_HWCR, hwcr);

                         /* McStatusWrEn has to be set */
                         need_toggle = !(hwcr & BIT(18));

                         if (need_toggle)
                                 wrmsrl(MSR_K7_HWCR, hwcr | BIT(18));

                         for (i = 0; i < ARRAY_SIZE(msrs); i++) {
                                 rdmsrl(msrs[i], val);

                                 /* CntP bit set? */
                                 if (val & BIT(62)) {
                                         val &= ~BIT(62);
                                         wrmsrl(msrs[i], val);
                                 }
                         }

                         /* restore old settings */
                         if (need_toggle)
                                 wrmsrl(MSR_K7_HWCR, hwcr);
                 }
        }

        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 && banks > 0)
                        mce_banks[0].init = 0;

                /*
                 * All newer Intel systems support MCE broadcasting. Enable
                 * synchronization with a one second timeout.
                 */
                if ((c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xe)) &&
                        monarch_timeout < 0)
                        monarch_timeout = USEC_PER_SEC;

                /*
                 * There are also broken BIOSes on some Pentium M and
                 * earlier systems:
                 */
                if (c->x86 == 6 && c->x86_model <= 13 && mce_bootlog < 0)
                        mce_bootlog = 0;
        }
        if (monarch_timeout < 0)
                monarch_timeout = 0;
        if (mce_bootlog != 0)
                mce_panic_timeout = 30;

        return 0;
}

static int __cpuinit __mcheck_cpu_ancient_init(struct cpuinfo_x86 *c)
{
        if (c->x86 != 5)
                return 0;

        switch (c->x86_vendor) {
        case X86_VENDOR_INTEL:
                intel_p5_mcheck_init(c);
                return 1;
                break;
        case X86_VENDOR_CENTAUR:
                winchip_mcheck_init(c);
                return 1;
                break;
        }

        return 0;
}

static void __mcheck_cpu_init_vendor(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 __mcheck_cpu_init_timer(void)
{
        struct timer_list *t = &__get_cpu_var(mce_timer);
        int *n = &__get_cpu_var(mce_next_interval);

        setup_timer(t, mce_start_timer, smp_processor_id());

        if (mce_ignore_ce)
                return;

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

/* 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;

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

        if (__mcheck_cpu_ancient_init(c))
                return;

        if (!mce_available(c))
                return;

        if (__mcheck_cpu_cap_init() < 0 || __mcheck_cpu_apply_quirks(c) < 0) {
                mce_disabled = 1;
                return;
        }

        machine_check_vector = do_machine_check;

        __mcheck_cpu_init_generic();
        __mcheck_cpu_init_vendor(c);
        __mcheck_cpu_init_timer();
        INIT_WORK(&__get_cpu_var(mce_work), mce_process_work);
        init_irq_work(&__get_cpu_var(mce_irq_work), &mce_irq_work_cb);
}

/*
 * mce_chrdev: Character device /dev/mcelog to read and clear the MCE log.
 */

static DEFINE_SPINLOCK(mce_chrdev_state_lock);
static int mce_chrdev_open_count;       /* #times opened */
static int mce_chrdev_open_exclu;       /* already open exclusive? */

static int mce_chrdev_open(struct inode *inode, struct file *file)
{
        spin_lock(&mce_chrdev_state_lock);

        if (mce_chrdev_open_exclu ||
            (mce_chrdev_open_count && (file->f_flags & O_EXCL))) {
                spin_unlock(&mce_chrdev_state_lock);

                return -EBUSY;
        }

        if (file->f_flags & O_EXCL)
                mce_chrdev_open_exclu = 1;
        mce_chrdev_open_count++;

        spin_unlock(&mce_chrdev_state_lock);

        return nonseekable_open(inode, file);
}

static int mce_chrdev_release(struct inode *inode, struct file *file)
{
        spin_lock(&mce_chrdev_state_lock);

        mce_chrdev_open_count--;
        mce_chrdev_open_exclu = 0;

        spin_unlock(&mce_chrdev_state_lock);

        return 0;
}

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

        rdtscll(cpu_tsc[smp_processor_id()]);
}

static int mce_apei_read_done;

/* Collect MCE record of previous boot in persistent storage via APEI ERST. */
static int __mce_read_apei(char __user **ubuf, size_t usize)
{
        int rc;
        u64 record_id;
        struct mce m;

        if (usize < sizeof(struct mce))
                return -EINVAL;

        rc = apei_read_mce(&m, &record_id);
        /* Error or no more MCE record */
        if (rc <= 0) {
                mce_apei_read_done = 1;
                /*
                 * When ERST is disabled, mce_chrdev_read() should return
                 * "no record" instead of "no device."
                 */
                if (rc == -ENODEV)
                        return 0;
                return rc;
        }
        rc = -EFAULT;
        if (copy_to_user(*ubuf, &m, sizeof(struct mce)))
                return rc;
        /*
         * In fact, we should have cleared the record after that has
         * been flushed to the disk or sent to network in
         * /sbin/mcelog, but we have no interface to support that now,
         * so just clear it to avoid duplication.
         */
        rc = apei_clear_mce(record_id);
        if (rc) {
                mce_apei_read_done = 1;
                return rc;
        }
        *ubuf += sizeof(struct mce);

        return 0;
}

static ssize_t mce_chrdev_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_chrdev_read_mutex);

        if (!mce_apei_read_done) {
                err = __mce_read_apei(&buf, usize);
                if (err || buf != ubuf)
                        goto out;
        }

        next = rcu_dereference_check_mce(mcelog.next);

        /* Only supports full reads right now */
        err = -EINVAL;
        if (*off != 0 || usize < MCE_LOG_LEN*sizeof(struct mce))
                goto out;

        err = 0;
        prev = 0;
        do {
                for (i = prev; i < next; i++) {
                        unsigned long start = jiffies;
                        struct mce *m = &mcelog.entry[i];

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

                if (m->finished && m->tsc < cpu_tsc[m->cpu]) {
                        err |= copy_to_user(buf, m, sizeof(*m));
                        smp_rmb();
                        buf += sizeof(*m);
                        memset(m, 0, sizeof(*m));
                }
        }

        if (err)
                err = -EFAULT;

out:
        mutex_unlock(&mce_chrdev_read_mutex);
        kfree(cpu_tsc);

        return err ? err : buf - ubuf;
}

static unsigned int mce_chrdev_poll(struct file *file, poll_table *wait)
{
        poll_wait(file, &mce_chrdev_wait, wait);
        if (rcu_access_index(mcelog.next))
                return POLLIN | POLLRDNORM;
        if (!mce_apei_read_done && apei_check_mce())
                return POLLIN | POLLRDNORM;
        return 0;
}

static long mce_chrdev_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;
        }
}

static ssize_t (*mce_write)(struct file *filp, const char __user *ubuf,
                            size_t usize, loff_t *off);

void register_mce_write_callback(ssize_t (*fn)(struct file *filp,
                             const char __user *ubuf,
                             size_t usize, loff_t *off))
{
        mce_write = fn;
}
EXPORT_SYMBOL_GPL(register_mce_write_callback);

ssize_t mce_chrdev_write(struct file *filp, const char __user *ubuf,
                         size_t usize, loff_t *off)
{
        if (mce_write)
                return mce_write(filp, ubuf, usize, off);
        else
                return -EINVAL;
}

static const struct file_operations mce_chrdev_ops = {
        .open                   = mce_chrdev_open,
        .release                = mce_chrdev_release,
        .read                   = mce_chrdev_read,
        .write                  = mce_chrdev_write,
        .poll                   = mce_chrdev_poll,
        .unlocked_ioctl         = mce_chrdev_ioctl,
        .llseek                 = no_llseek,
};

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

/*
 * mce=off Disables machine check
 * mce=no_cmci Disables CMCI
 * mce=dont_log_ce Clears corrected events silently, no log created for CEs.
 * mce=ignore_ce Disables polling and CMCI, corrected events are not cleared.
 * mce=TOLERANCELEVEL[,monarchtimeout] (number, see above)
 *      monarchtimeout is how long to wait for other CPUs on machine
 *      check, or 0 to not wait
 * 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();
                return 1;
        }
        if (*str == '=')
                str++;
        if (!strcmp(str, "off"))
                mce_disabled = 1;
        else if (!strcmp(str, "no_cmci"))
                mce_cmci_disabled = 1;
        else if (!strcmp(str, "dont_log_ce"))
                mce_dont_log_ce = 1;
        else if (!strcmp(str, "ignore_ce"))
                mce_ignore_ce = 1;
        else if (!strcmp(str, "bootlog") || !strcmp(str, "nobootlog"))
                mce_bootlog = (str[0] == 'b');
        else if (isdigit(str[0])) {
                get_option(&str, &tolerant);
                if (*str == ',') {
                        ++str;
                        get_option(&str, &monarch_timeout);
                }
        } else {
                printk(KERN_INFO "mce argument %s ignored. Please use /sys\n",
                       str);
                return 0;
        }
        return 1;
}
__setup("mce", mcheck_enable);

int __init mcheck_init(void)
{
        mcheck_intel_therm_init();

        return 0;
}

/*
 * mce_syscore: PM support
 */

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

        for (i = 0; i < banks; i++) {
                struct mce_bank *b = &mce_banks[i];

                if (b->init)
                        wrmsrl(MSR_IA32_MCx_CTL(i), 0);
        }
        return 0;
}

static int mce_syscore_suspend(void)
{
        return mce_disable_error_reporting();
}

static void mce_syscore_shutdown(void)
{
        mce_disable_error_reporting();
}

/*
 * 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 void mce_syscore_resume(void)
{
        __mcheck_cpu_init_generic();
        __mcheck_cpu_init_vendor(__this_cpu_ptr(&cpu_info));
}

static struct syscore_ops mce_syscore_ops = {
        .suspend        = mce_syscore_suspend,
        .shutdown       = mce_syscore_shutdown,
        .resume         = mce_syscore_resume,
};

/*
 * mce_device: Sysfs support
 */

static void mce_cpu_restart(void *data)
{
        if (!mce_available(__this_cpu_ptr(&cpu_info)))
                return;
        __mcheck_cpu_init_generic();
        __mcheck_cpu_init_timer();
}

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

/* Toggle features for corrected errors */
static void mce_disable_cmci(void *data)
{
        if (!mce_available(__this_cpu_ptr(&cpu_info)))
                return;
        cmci_clear();
}

static void mce_enable_ce(void *all)
{
        if (!mce_available(__this_cpu_ptr(&cpu_info)))
                return;
        cmci_reenable();
        cmci_recheck();
        if (all)
                __mcheck_cpu_init_timer();
}

static struct bus_type mce_subsys = {
        .name           = "machinecheck",
        .dev_name       = "machinecheck",
};

DEFINE_PER_CPU(struct device *, mce_device);

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

static inline struct mce_bank *attr_to_bank(struct device_attribute *attr)
{
        return container_of(attr, struct mce_bank, attr);
}

static ssize_t show_bank(struct device *s, struct device_attribute *attr,
                         char *buf)
{
        return sprintf(buf, "%llx\n", attr_to_bank(attr)->ctl);
}

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

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

        attr_to_bank(attr)->ctl = new;
        mce_restart();

        return size;
}

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

static ssize_t set_trigger(struct device *s, struct device_attribute *attr,
                                const char *buf, size_t siz)
{
        char *p;

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

        if (p)
                *p = 0;

        return strlen(mce_helper) + !!p;
}

static ssize_t set_ignore_ce(struct device *s,
                             struct device_attribute *attr,
                             const char *buf, size_t size)
{
        u64 new;

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

        if (mce_ignore_ce ^ !!new) {
                if (new) {
                        /* disable ce features */
                        mce_timer_delete_all();
                        on_each_cpu(mce_disable_cmci, NULL, 1);
                        mce_ignore_ce = 1;
                } else {
                        /* enable ce features */
                        mce_ignore_ce = 0;
                        on_each_cpu(mce_enable_ce, (void *)1, 1);
                }
        }
        return size;
}

static ssize_t set_cmci_disabled(struct device *s,
                                 struct device_attribute *attr,
                                 const char *buf, size_t size)
{
        u64 new;

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

        if (mce_cmci_disabled ^ !!new) {
                if (new) {
                        /* disable cmci */
                        on_each_cpu(mce_disable_cmci, NULL, 1);
                        mce_cmci_disabled = 1;
                } else {
                        /* enable cmci */
                        mce_cmci_disabled = 0;
                        on_each_cpu(mce_enable_ce, NULL, 1);
                }
        }
        return size;
}

static ssize_t store_int_with_restart(struct device *s,
                                      struct device_attribute *attr,
                                      const char *buf, size_t size)
{
        ssize_t ret = device_store_int(s, attr, buf, size);
        mce_restart();
        return ret;
}

static DEVICE_ATTR(trigger, 0644, show_trigger, set_trigger);
static DEVICE_INT_ATTR(tolerant, 0644, tolerant);
static DEVICE_INT_ATTR(monarch_timeout, 0644, monarch_timeout);
static DEVICE_INT_ATTR(dont_log_ce, 0644, mce_dont_log_ce);

static struct dev_ext_attribute dev_attr_check_interval = {
        __ATTR(check_interval, 0644, device_show_int, store_int_with_restart),
        &check_interval
};

static struct dev_ext_attribute dev_attr_ignore_ce = {
        __ATTR(ignore_ce, 0644, device_show_int, set_ignore_ce),
        &mce_ignore_ce
};

static struct dev_ext_attribute dev_attr_cmci_disabled = {
        __ATTR(cmci_disabled, 0644, device_show_int, set_cmci_disabled),
        &mce_cmci_disabled
};

static struct device_attribute *mce_device_attrs[] = {
        &dev_attr_tolerant.attr,
        &dev_attr_check_interval.attr,
        &dev_attr_trigger,
        &dev_attr_monarch_timeout.attr,
        &dev_attr_dont_log_ce.attr,
        &dev_attr_ignore_ce.attr,
        &dev_attr_cmci_disabled.attr,
        NULL
};

static cpumask_var_t mce_device_initialized;

static void mce_device_release(struct device *dev)
{
        kfree(dev);
}

/* Per cpu device init. All of the cpus still share the same ctrl bank: */
static __cpuinit int mce_device_create(unsigned int cpu)
{
        struct device *dev;
        int err;
        int i, j;

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

        dev = kzalloc(sizeof *dev, GFP_KERNEL);
        if (!dev)
                return -ENOMEM;
        dev->id  = cpu;
        dev->bus = &mce_subsys;
        dev->release = &mce_device_release;

        err = device_register(dev);
        if (err)
                return err;

        for (i = 0; mce_device_attrs[i]; i++) {
                err = device_create_file(dev, mce_device_attrs[i]);
                if (err)
                        goto error;
        }
        for (j = 0; j < banks; j++) {
                err = device_create_file(dev, &mce_banks[j].attr);
                if (err)
                        goto error2;
        }
        cpumask_set_cpu(cpu, mce_device_initialized);
        per_cpu(mce_device, cpu) = dev;

        return 0;
error2:
        while (--j >= 0)
                device_remove_file(dev, &mce_banks[j].attr);
error:
        while (--i >= 0)
                device_remove_file(dev, mce_device_attrs[i]);

        device_unregister(dev);

        return err;
}

static __cpuinit void mce_device_remove(unsigned int cpu)
{
        struct device *dev = per_cpu(mce_device, cpu);
        int i;

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

        for (i = 0; mce_device_attrs[i]; i++)
                device_remove_file(dev, mce_device_attrs[i]);

        for (i = 0; i < banks; i++)
                device_remove_file(dev, &mce_banks[i].attr);

        device_unregister(dev);
        cpumask_clear_cpu(cpu, mce_device_initialized);
        per_cpu(mce_device, cpu) = NULL;
}

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

        if (!mce_available(__this_cpu_ptr(&cpu_info)))
                return;

        if (!(action & CPU_TASKS_FROZEN))
                cmci_clear();
        for (i = 0; i < banks; i++) {
                struct mce_bank *b = &mce_banks[i];

                if (b->init)
                        wrmsrl(MSR_IA32_MCx_CTL(i), 0);
        }
}

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

        if (!mce_available(__this_cpu_ptr(&cpu_info)))
                return;

        if (!(action & CPU_TASKS_FROZEN))
                cmci_reenable();
        for (i = 0; i < banks; i++) {
                struct mce_bank *b = &mce_banks[i];

                if (b->init)
                        wrmsrl(MSR_IA32_MCx_CTL(i), b->ctl);
        }
}

/* 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_device_create(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_device_remove(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:
                if (!mce_ignore_ce && check_interval) {
                        t->expires = round_jiffies(jiffies +
                                           __get_cpu_var(mce_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 void mce_init_banks(void)
{
        int i;

        for (i = 0; i < banks; i++) {
                struct mce_bank *b = &mce_banks[i];
                struct device_attribute *a = &b->attr;

                sysfs_attr_init(&a->attr);
                a->attr.name    = b->attrname;
                snprintf(b->attrname, ATTR_LEN, "bank%d", i);

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

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

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

        zalloc_cpumask_var(&mce_device_initialized, GFP_KERNEL);

        mce_init_banks();

        err = subsys_system_register(&mce_subsys, NULL);
        if (err)
                return err;

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

        register_syscore_ops(&mce_syscore_ops);
        register_hotcpu_notifier(&mce_cpu_notifier);

        /* register character device /dev/mcelog */
        misc_register(&mce_chrdev_device);

        return err;
}
device_initcall(mcheck_init_device);

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

#ifdef CONFIG_DEBUG_FS
struct dentry *mce_get_debugfs_dir(void)
{
        static struct dentry *dmce;

        if (!dmce)
                dmce = debugfs_create_dir("mce", NULL);

        return dmce;
}

static void mce_reset(void)
{
        cpu_missing = 0;
        atomic_set(&mce_fake_paniced, 0);
        atomic_set(&mce_executing, 0);
        atomic_set(&mce_callin, 0);
        atomic_set(&global_nwo, 0);
}

static int fake_panic_get(void *data, u64 *val)
{
        *val = fake_panic;
        return 0;
}

static int fake_panic_set(void *data, u64 val)
{
        mce_reset();
        fake_panic = val;
        return 0;
}

DEFINE_SIMPLE_ATTRIBUTE(fake_panic_fops, fake_panic_get,
                        fake_panic_set, "%llu\n");

static int __init mcheck_debugfs_init(void)
{
        struct dentry *dmce, *ffake_panic;

        dmce = mce_get_debugfs_dir();
        if (!dmce)
                return -ENOMEM;
        ffake_panic = debugfs_create_file("fake_panic", 0444, dmce, NULL,
                                          &fake_panic_fops);
        if (!ffake_panic)
                return -ENOMEM;

        return 0;
}
late_initcall(mcheck_debugfs_init);
#endif