arch/x86/kernel/msr.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
   5  *
   6  *   This program is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU General Public License as published by
   8  *   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
   9  *   USA; either version 2 of the License, or (at your option) any later
  10  *   version; incorporated herein by reference.
  11  *
  12  * ----------------------------------------------------------------------- */
  13
  14 /*
  15  * x86 MSR access device
  16  *
  17  * This device is accessed by lseek() to the appropriate register number
  18  * and then read/write in chunks of 8 bytes.  A larger size means multiple
  19  * reads or writes of the same register.
  20  *
  21  * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
  22  * an SMP box will direct the access to CPU %d.
  23  */
  24
  25 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  26
  27 #include <linux/module.h>
  28
  29 #include <linux/types.h>
  30 #include <linux/errno.h>
  31 #include <linux/fcntl.h>
  32 #include <linux/init.h>
  33 #include <linux/poll.h>
  34 #include <linux/smp.h>
  35 #include <linux/major.h>
  36 #include <linux/fs.h>
  37 #include <linux/device.h>
  38 #include <linux/cpu.h>
  39 #include <linux/notifier.h>
  40 #include <linux/uaccess.h>
  41 #include <linux/gfp.h>
  42
  43 #include <asm/cpufeature.h>
  44 #include <asm/msr.h>
  45
  46 static struct class *msr_class;
  47 static enum cpuhp_state cpuhp_msr_state;
  48
  49 static ssize_t msr_read(struct file *file, char __user *buf,
  50                         size_t count, loff_t *ppos)
  51 {
  52         u32 __user *tmp = (u32 __user *) buf;
  53         u32 data[2];
  54         u32 reg = *ppos;
  55         int cpu = iminor(file_inode(file));
  56         int err = 0;
  57         ssize_t bytes = 0;
  58
  59         if (count % 8)
  60                 return -EINVAL; /* Invalid chunk size */
  61
  62         for (; count; count -= 8) {
  63                 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
  64                 if (err)
  65                         break;
  66                 if (copy_to_user(tmp, &data, 8)) {
  67                         err = -EFAULT;
  68                         break;
  69                 }
  70                 tmp += 2;
  71                 bytes += 8;
  72         }
  73
  74         return bytes ? bytes : err;
  75 }
  76
  77 static ssize_t msr_write(struct file *file, const char __user *buf,
  78                          size_t count, loff_t *ppos)
  79 {
  80         const u32 __user *tmp = (const u32 __user *)buf;
  81         u32 data[2];
  82         u32 reg = *ppos;
  83         int cpu = iminor(file_inode(file));
  84         int err = 0;
  85         ssize_t bytes = 0;
  86
  87         if (kernel_is_locked_down())
  88                 return -EPERM;
  89
  90         if (count % 8)
  91                 return -EINVAL; /* Invalid chunk size */
  92
  93         for (; count; count -= 8) {
  94                 if (copy_from_user(&data, tmp, 8)) {
  95                         err = -EFAULT;
  96                         break;
  97                 }
  98                 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
  99                 if (err)
 100                         break;
 101                 tmp += 2;
 102                 bytes += 8;
 103         }
 104
 105         return bytes ? bytes : err;
 106 }
 107
 108 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 109 {
 110         u32 __user *uregs = (u32 __user *)arg;
 111         u32 regs[8];
 112         int cpu = iminor(file_inode(file));
 113         int err;
 114
 115         switch (ioc) {
 116         case X86_IOC_RDMSR_REGS:
 117                 if (!(file->f_mode & FMODE_READ)) {
 118                         err = -EBADF;
 119                         break;
 120                 }
 121                 if (copy_from_user(&regs, uregs, sizeof regs)) {
 122                         err = -EFAULT;
 123                         break;
 124                 }
 125                 err = rdmsr_safe_regs_on_cpu(cpu, regs);
 126                 if (err)
 127                         break;
 128                 if (copy_to_user(uregs, &regs, sizeof regs))
 129                         err = -EFAULT;
 130                 break;
 131
 132         case X86_IOC_WRMSR_REGS:
 133                 if (!(file->f_mode & FMODE_WRITE)) {
 134                         err = -EBADF;
 135                         break;
 136                 }
 137                 if (kernel_is_locked_down()) {
 138                         err = -EPERM;
 139                         break;
 140                 }
 141                 if (copy_from_user(&regs, uregs, sizeof regs)) {
 142                         err = -EFAULT;
 143                         break;
 144                 }
 145                 err = wrmsr_safe_regs_on_cpu(cpu, regs);
 146                 if (err)
 147                         break;
 148                 if (copy_to_user(uregs, &regs, sizeof regs))
 149                         err = -EFAULT;
 150                 break;
 151
 152         default:
 153                 err = -ENOTTY;
 154                 break;
 155         }
 156
 157         return err;
 158 }
 159
 160 static int msr_open(struct inode *inode, struct file *file)
 161 {
 162         unsigned int cpu = iminor(file_inode(file));
 163         struct cpuinfo_x86 *c;
 164
 165         if (!capable(CAP_SYS_RAWIO))
 166                 return -EPERM;
 167
 168         if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 169                 return -ENXIO;  /* No such CPU */
 170
 171         c = &cpu_data(cpu);
 172         if (!cpu_has(c, X86_FEATURE_MSR))
 173                 return -EIO;    /* MSR not supported */
 174
 175         return 0;
 176 }
 177
 178 /*
 179  * File operations we support
 180  */
 181 static const struct file_operations msr_fops = {
 182         .owner = THIS_MODULE,
 183         .llseek = no_seek_end_llseek,
 184         .read = msr_read,
 185         .write = msr_write,
 186         .open = msr_open,
 187         .unlocked_ioctl = msr_ioctl,
 188         .compat_ioctl = msr_ioctl,
 189 };
 190
 191 static int msr_device_create(unsigned int cpu)
 192 {
 193         struct device *dev;
 194
 195         dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
 196                             "msr%d", cpu);
 197         return PTR_ERR_OR_ZERO(dev);
 198 }
 199
 200 static int msr_device_destroy(unsigned int cpu)
 201 {
 202         device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
 203         return 0;
 204 }
 205
 206 static char *msr_devnode(struct device *dev, umode_t *mode)
 207 {
 208         return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
 209 }
 210
 211 static int __init msr_init(void)
 212 {
 213         int err;
 214
 215         if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
 216                 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
 217                 return -EBUSY;
 218         }
 219         msr_class = class_create(THIS_MODULE, "msr");
 220         if (IS_ERR(msr_class)) {
 221                 err = PTR_ERR(msr_class);
 222                 goto out_chrdev;
 223         }
 224         msr_class->devnode = msr_devnode;
 225
 226         err  = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
 227                                  msr_device_create, msr_device_destroy);
 228         if (err < 0)
 229                 goto out_class;
 230         cpuhp_msr_state = err;
 231         return 0;
 232
 233 out_class:
 234         class_destroy(msr_class);
 235 out_chrdev:
 236         __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
 237         return err;
 238 }
 239 module_init(msr_init);
 240
 241 static void __exit msr_exit(void)
 242 {
 243         cpuhp_remove_state(cpuhp_msr_state);
 244         class_destroy(msr_class);
 245         __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
 246 }
 247 module_exit(msr_exit)
 248
 249 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
 250 MODULE_DESCRIPTION("x86 generic MSR driver");
 251 MODULE_LICENSE("GPL");