arch/x86/kernel/cpu/mcheck/dev-mcelog.c

/*
 * /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);