/*
 * /dev/mcelog driver
 *
 * 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
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/poll.h>

#include "mce-internal.h"

static DEFINE_MUTEX(mce_chrdev_read_mutex);

static char mce_helper[128];
static char *mce_helper_argv[2] = { mce_helper, NULL };

#define mce_log_get_idx_check(p) \
({ \
        RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() && \
                         !lockdep_is_held(&mce_chrdev_read_mutex), \
                         "suspicious mce_log_get_idx_check() usage"); \
        smp_load_acquire(&(p)); \
})

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

static DECLARE_WAIT_QUEUE_HEAD(mce_chrdev_wait);

/* User mode helper program triggered by machine check event */
extern char                     mce_helper[128];

static int dev_mce_log(struct notifier_block *nb, unsigned long val,
                                void *data)
{
        struct mce *mce = (struct mce *)data;
        unsigned int next, entry;

        wmb();
        for (;;) {
                entry = mce_log_get_idx_check(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 NOTIFY_OK;
                        }
                        /* 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();

        /* wake processes polling /dev/mcelog */
        wake_up_interruptible(&mce_chrdev_wait);

        return NOTIFY_OK;
}

static struct notifier_block dev_mcelog_nb = {
        .notifier_call  = dev_mce_log,
        .priority       = MCE_PRIO_MCELOG,
};

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);


void mce_work_trigger(void)
{
        if (mce_helper[0])
                schedule_work(&mce_trigger_work);
}

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;
}

DEVICE_ATTR(trigger, 0644, show_trigger, set_trigger);

/*
 * 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;

        cpu_tsc[smp_processor_id()] = rdtsc();
}

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 = mce_log_get_idx_check(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 (READ_ONCE(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);

static 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,
};

static __init int dev_mcelog_init_device(void)
{
        int err;

        /* register character device /dev/mcelog */
        err = misc_register(&mce_chrdev_device);
        if (err) {
                pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
                return err;
        }
        mce_register_decode_chain(&dev_mcelog_nb);
        return 0;
}
device_initcall_sync(dev_mcelog_init_device);