arch/x86/kernel/msr.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
   4  *
   5  *   This program is free software; you can redistribute it and/or modify
   6  *   it under the terms of the GNU General Public License as published by
   7  *   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
   8  *   USA; either version 2 of the License, or (at your option) any later
   9  *   version; incorporated herein by reference.
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 /*
  14  * x86 MSR access device
  15  *
  16  * This device is accessed by lseek() to the appropriate register number
  17  * and then read/write in chunks of 8 bytes.  A larger size means multiple
  18  * reads or writes of the same register.
  19  *
  20  * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
  21  * an SMP box will direct the access to CPU %d.
  22  */
  23
  24 #include <linux/module.h>
  25
  26 #include <linux/types.h>
  27 #include <linux/errno.h>
  28 #include <linux/fcntl.h>
  29 #include <linux/init.h>
  30 #include <linux/poll.h>
  31 #include <linux/smp.h>
  32 #include <linux/smp_lock.h>
  33 #include <linux/major.h>
  34 #include <linux/fs.h>
  35 #include <linux/device.h>
  36 #include <linux/cpu.h>
  37 #include <linux/notifier.h>
  38 #include <linux/uaccess.h>
  39
  40 #include <asm/processor.h>
  41 #include <asm/msr.h>
  42 #include <asm/system.h>
  43
  44 static struct class *msr_class;
  45
  46 static loff_t msr_seek(struct file *file, loff_t offset, int orig)
  47 {
  48         loff_t ret;
  49         struct inode *inode = file->f_mapping->host;
  50
  51         mutex_lock(&inode->i_mutex);
  52         switch (orig) {
  53         case 0:
  54                 file->f_pos = offset;
  55                 ret = file->f_pos;
  56                 break;
  57         case 1:
  58                 file->f_pos += offset;
  59                 ret = file->f_pos;
  60                 break;
  61         default:
  62                 ret = -EINVAL;
  63         }
  64         mutex_unlock(&inode->i_mutex);
  65         return ret;
  66 }
  67
  68 static ssize_t msr_read(struct file *file, char __user *buf,
  69                         size_t count, loff_t *ppos)
  70 {
  71         u32 __user *tmp = (u32 __user *) buf;
  72         u32 data[2];
  73         u32 reg = *ppos;
  74         int cpu = iminor(file->f_path.dentry->d_inode);
  75         int err = 0;
  76         ssize_t bytes = 0;
  77
  78         if (count % 8)
  79                 return -EINVAL; /* Invalid chunk size */
  80
  81         for (; count; count -= 8) {
  82                 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
  83                 if (err) {
  84                         if (err == -EFAULT) /* Fix idiotic error code */
  85                                 err = -EIO;
  86                         break;
  87                 }
  88                 if (copy_to_user(tmp, &data, 8)) {
  89                         err = -EFAULT;
  90                         break;
  91                 }
  92                 tmp += 2;
  93                 bytes += 8;
  94         }
  95
  96         return bytes ? bytes : err;
  97 }
  98
  99 static ssize_t msr_write(struct file *file, const char __user *buf,
 100                          size_t count, loff_t *ppos)
 101 {
 102         const u32 __user *tmp = (const u32 __user *)buf;
 103         u32 data[2];
 104         u32 reg = *ppos;
 105         int cpu = iminor(file->f_path.dentry->d_inode);
 106         int err = 0;
 107         ssize_t bytes = 0;
 108
 109         if (count % 8)
 110                 return -EINVAL; /* Invalid chunk size */
 111
 112         for (; count; count -= 8) {
 113                 if (copy_from_user(&data, tmp, 8)) {
 114                         err = -EFAULT;
 115                         break;
 116                 }
 117                 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
 118                 if (err) {
 119                         if (err == -EFAULT) /* Fix idiotic error code */
 120                                 err = -EIO;
 121                         break;
 122                 }
 123                 tmp += 2;
 124                 bytes += 8;
 125         }
 126
 127         return bytes ? bytes : err;
 128 }
 129
 130 static int msr_open(struct inode *inode, struct file *file)
 131 {
 132         unsigned int cpu = iminor(file->f_path.dentry->d_inode);
 133         struct cpuinfo_x86 *c = &cpu_data(cpu);
 134         int ret = 0;
 135
 136         lock_kernel();
 137         cpu = iminor(file->f_path.dentry->d_inode);
 138
 139         if (cpu >= nr_cpu_ids || !cpu_online(cpu)) {
 140                 ret = -ENXIO;   /* No such CPU */
 141                 goto out;
 142         }
 143         c = &cpu_data(cpu);
 144         if (!cpu_has(c, X86_FEATURE_MSR))
 145                 ret = -EIO;     /* MSR not supported */
 146 out:
 147         unlock_kernel();
 148         return ret;
 149 }
 150
 151 /*
 152  * File operations we support
 153  */
 154 static const struct file_operations msr_fops = {
 155         .owner = THIS_MODULE,
 156         .llseek = msr_seek,
 157         .read = msr_read,
 158         .write = msr_write,
 159         .open = msr_open,
 160 };
 161
 162 static int __cpuinit msr_device_create(int cpu)
 163 {
 164         struct device *dev;
 165
 166         dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
 167                             "msr%d", cpu);
 168         return IS_ERR(dev) ? PTR_ERR(dev) : 0;
 169 }
 170
 171 static void msr_device_destroy(int cpu)
 172 {
 173         device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
 174 }
 175
 176 static int __cpuinit msr_class_cpu_callback(struct notifier_block *nfb,
 177                                 unsigned long action, void *hcpu)
 178 {
 179         unsigned int cpu = (unsigned long)hcpu;
 180         int err = 0;
 181
 182         switch (action) {
 183         case CPU_UP_PREPARE:
 184                 err = msr_device_create(cpu);
 185                 break;
 186         case CPU_UP_CANCELED:
 187         case CPU_UP_CANCELED_FROZEN:
 188         case CPU_DEAD:
 189                 msr_device_destroy(cpu);
 190                 break;
 191         }
 192         return err ? NOTIFY_BAD : NOTIFY_OK;
 193 }
 194
 195 static struct notifier_block __refdata msr_class_cpu_notifier = {
 196         .notifier_call = msr_class_cpu_callback,
 197 };
 198
 199 static char *msr_nodename(struct device *dev)
 200 {
 201         return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
 202 }
 203
 204 static int __init msr_init(void)
 205 {
 206         int i, err = 0;
 207         i = 0;
 208
 209         if (register_chrdev(MSR_MAJOR, "cpu/msr", &msr_fops)) {
 210                 printk(KERN_ERR "msr: unable to get major %d for msr\n",
 211                        MSR_MAJOR);
 212                 err = -EBUSY;
 213                 goto out;
 214         }
 215         msr_class = class_create(THIS_MODULE, "msr");
 216         if (IS_ERR(msr_class)) {
 217                 err = PTR_ERR(msr_class);
 218                 goto out_chrdev;
 219         }
 220         msr_class->nodename = msr_nodename;
 221         for_each_online_cpu(i) {
 222                 err = msr_device_create(i);
 223                 if (err != 0)
 224                         goto out_class;
 225         }
 226         register_hotcpu_notifier(&msr_class_cpu_notifier);
 227
 228         err = 0;
 229         goto out;
 230
 231 out_class:
 232         i = 0;
 233         for_each_online_cpu(i)
 234                 msr_device_destroy(i);
 235         class_destroy(msr_class);
 236 out_chrdev:
 237         unregister_chrdev(MSR_MAJOR, "cpu/msr");
 238 out:
 239         return err;
 240 }
 241
 242 static void __exit msr_exit(void)
 243 {
 244         int cpu = 0;
 245         for_each_online_cpu(cpu)
 246                 msr_device_destroy(cpu);
 247         class_destroy(msr_class);
 248         unregister_chrdev(MSR_MAJOR, "cpu/msr");
 249         unregister_hotcpu_notifier(&msr_class_cpu_notifier);
 250 }
 251
 252 module_init(msr_init);
 253 module_exit(msr_exit)
 254
 255 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
 256 MODULE_DESCRIPTION("x86 generic MSR driver");
 257 MODULE_LICENSE("GPL");