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msr.c

/* ----------------------------------------------------------------------- *
 *   
 *   Copyright 2000 H. Peter Anvin - All Rights Reserved
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
 *   USA; either version 2 of the License, or (at your option) any later
 *   version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * x86 MSR access device
 *
 * This device is accessed by lseek() to the appropriate register number
 * and then read/write in chunks of 8 bytes.  A larger size means multiple
 * reads or writes of the same register.
 *
 * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
 * an SMP box will direct the access to CPU %d.
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/major.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <linux/notifier.h>

#include <asm/processor.h>
#include <asm/msr.h>
#include <asm/uaccess.h>
#include <asm/system.h>

static struct class *msr_class;

static loff_t msr_seek(struct file *file, loff_t offset, int orig)
{
      loff_t ret = -EINVAL;

      lock_kernel();
      switch (orig) {
      case 0:
            file->f_pos = offset;
            ret = file->f_pos;
            break;
      case 1:
            file->f_pos += offset;
            ret = file->f_pos;
      }
      unlock_kernel();
      return ret;
}

static ssize_t msr_read(struct file *file, char __user * buf,
                  size_t count, loff_t * ppos)
{
      u32 __user *tmp = (u32 __user *) buf;
      u32 data[2];
      u32 reg = *ppos;
      int cpu = iminor(file->f_path.dentry->d_inode);
      int err;

      if (count % 8)
            return -EINVAL;   /* Invalid chunk size */

      for (; count; count -= 8) {
            err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
            if (err)
                  return -EIO;
            if (copy_to_user(tmp, &data, 8))
                  return -EFAULT;
            tmp += 2;
      }

      return ((char __user *)tmp) - buf;
}

static ssize_t msr_write(struct file *file, const char __user *buf,
                   size_t count, loff_t *ppos)
{
      const u32 __user *tmp = (const u32 __user *)buf;
      u32 data[2];
      u32 reg = *ppos;
      int cpu = iminor(file->f_path.dentry->d_inode);
      int err;

      if (count % 8)
            return -EINVAL;   /* Invalid chunk size */

      for (; count; count -= 8) {
            if (copy_from_user(&data, tmp, 8))
                  return -EFAULT;
            err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
            if (err)
                  return -EIO;
            tmp += 2;
      }

      return ((char __user *)tmp) - buf;
}

static int msr_open(struct inode *inode, struct file *file)
{
      unsigned int cpu = iminor(file->f_path.dentry->d_inode);
      struct cpuinfo_x86 *c = &cpu_data(cpu);

      if (cpu >= NR_CPUS || !cpu_online(cpu))
            return -ENXIO;    /* No such CPU */
      if (!cpu_has(c, X86_FEATURE_MSR))
            return -EIO;      /* MSR not supported */

      return 0;
}

/*
 * File operations we support
 */
static const struct file_operations msr_fops = {
      .owner = THIS_MODULE,
      .llseek = msr_seek,
      .read = msr_read,
      .write = msr_write,
      .open = msr_open,
};

static int __cpuinit msr_device_create(int cpu)
{
      struct device *dev;

      dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu),
                      "msr%d", cpu);
      return IS_ERR(dev) ? PTR_ERR(dev) : 0;
}

static void msr_device_destroy(int cpu)
{
      device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
}

static int __cpuinit msr_class_cpu_callback(struct notifier_block *nfb,
                        unsigned long action, void *hcpu)
{
      unsigned int cpu = (unsigned long)hcpu;
      int err = 0;

      switch (action) {
      case CPU_UP_PREPARE:
      case CPU_UP_PREPARE_FROZEN:
            err = msr_device_create(cpu);
            break;
      case CPU_UP_CANCELED:
      case CPU_UP_CANCELED_FROZEN:
      case CPU_DEAD:
      case CPU_DEAD_FROZEN:
            msr_device_destroy(cpu);
            break;
      }
      return err ? NOTIFY_BAD : NOTIFY_OK;
}

static struct notifier_block __cpuinitdata msr_class_cpu_notifier = {
      .notifier_call = msr_class_cpu_callback,
};

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

      if (register_chrdev(MSR_MAJOR, "cpu/msr", &msr_fops)) {
            printk(KERN_ERR "msr: unable to get major %d for msr\n",
                   MSR_MAJOR);
            err = -EBUSY;
            goto out;
      }
      msr_class = class_create(THIS_MODULE, "msr");
      if (IS_ERR(msr_class)) {
            err = PTR_ERR(msr_class);
            goto out_chrdev;
      }
      for_each_online_cpu(i) {
            err = msr_device_create(i);
            if (err != 0)
                  goto out_class;
      }
      register_hotcpu_notifier(&msr_class_cpu_notifier);

      err = 0;
      goto out;

out_class:
      i = 0;
      for_each_online_cpu(i)
            msr_device_destroy(i);
      class_destroy(msr_class);
out_chrdev:
      unregister_chrdev(MSR_MAJOR, "cpu/msr");
out:
      return err;
}

static void __exit msr_exit(void)
{
      int cpu = 0;
      for_each_online_cpu(cpu)
            msr_device_destroy(cpu);
      class_destroy(msr_class);
      unregister_chrdev(MSR_MAJOR, "cpu/msr");
      unregister_hotcpu_notifier(&msr_class_cpu_notifier);
}

module_init(msr_init);
module_exit(msr_exit)

MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
MODULE_DESCRIPTION("x86 generic MSR driver");
MODULE_LICENSE("GPL");

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