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
msr_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)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
msr_write(struct file * file,const char __user * buf,size_t count,loff_t * ppos)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 (count % 8)
88 return -EINVAL; /* Invalid chunk size */
89
90 for (; count; count -= 8) {
91 if (copy_from_user(&data, tmp, 8)) {
92 err = -EFAULT;
93 break;
94 }
95 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
96 if (err)
97 break;
98 tmp += 2;
99 bytes += 8;
100 }
101
102 return bytes ? bytes : err;
103 }
104
msr_ioctl(struct file * file,unsigned int ioc,unsigned long arg)105 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
106 {
107 u32 __user *uregs = (u32 __user *)arg;
108 u32 regs[8];
109 int cpu = iminor(file_inode(file));
110 int err;
111
112 switch (ioc) {
113 case X86_IOC_RDMSR_REGS:
114 if (!(file->f_mode & FMODE_READ)) {
115 err = -EBADF;
116 break;
117 }
118 if (copy_from_user(®s, uregs, sizeof regs)) {
119 err = -EFAULT;
120 break;
121 }
122 err = rdmsr_safe_regs_on_cpu(cpu, regs);
123 if (err)
124 break;
125 if (copy_to_user(uregs, ®s, sizeof regs))
126 err = -EFAULT;
127 break;
128
129 case X86_IOC_WRMSR_REGS:
130 if (!(file->f_mode & FMODE_WRITE)) {
131 err = -EBADF;
132 break;
133 }
134 if (copy_from_user(®s, uregs, sizeof regs)) {
135 err = -EFAULT;
136 break;
137 }
138 err = wrmsr_safe_regs_on_cpu(cpu, regs);
139 if (err)
140 break;
141 if (copy_to_user(uregs, ®s, sizeof regs))
142 err = -EFAULT;
143 break;
144
145 default:
146 err = -ENOTTY;
147 break;
148 }
149
150 return err;
151 }
152
msr_open(struct inode * inode,struct file * file)153 static int msr_open(struct inode *inode, struct file *file)
154 {
155 unsigned int cpu = iminor(file_inode(file));
156 struct cpuinfo_x86 *c;
157
158 if (!capable(CAP_SYS_RAWIO))
159 return -EPERM;
160
161 if (cpu >= nr_cpu_ids || !cpu_online(cpu))
162 return -ENXIO; /* No such CPU */
163
164 c = &cpu_data(cpu);
165 if (!cpu_has(c, X86_FEATURE_MSR))
166 return -EIO; /* MSR not supported */
167
168 return 0;
169 }
170
171 /*
172 * File operations we support
173 */
174 static const struct file_operations msr_fops = {
175 .owner = THIS_MODULE,
176 .llseek = no_seek_end_llseek,
177 .read = msr_read,
178 .write = msr_write,
179 .open = msr_open,
180 .unlocked_ioctl = msr_ioctl,
181 .compat_ioctl = msr_ioctl,
182 };
183
msr_device_create(unsigned int cpu)184 static int msr_device_create(unsigned int cpu)
185 {
186 struct device *dev;
187
188 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
189 "msr%d", cpu);
190 return PTR_ERR_OR_ZERO(dev);
191 }
192
msr_device_destroy(unsigned int cpu)193 static int msr_device_destroy(unsigned int cpu)
194 {
195 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
196 return 0;
197 }
198
msr_devnode(struct device * dev,umode_t * mode)199 static char *msr_devnode(struct device *dev, umode_t *mode)
200 {
201 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
202 }
203
msr_init(void)204 static int __init msr_init(void)
205 {
206 int err;
207
208 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
209 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
210 return -EBUSY;
211 }
212 msr_class = class_create(THIS_MODULE, "msr");
213 if (IS_ERR(msr_class)) {
214 err = PTR_ERR(msr_class);
215 goto out_chrdev;
216 }
217 msr_class->devnode = msr_devnode;
218
219 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
220 msr_device_create, msr_device_destroy);
221 if (err < 0)
222 goto out_class;
223 cpuhp_msr_state = err;
224 return 0;
225
226 out_class:
227 class_destroy(msr_class);
228 out_chrdev:
229 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
230 return err;
231 }
232 module_init(msr_init);
233
msr_exit(void)234 static void __exit msr_exit(void)
235 {
236 cpuhp_remove_state(cpuhp_msr_state);
237 class_destroy(msr_class);
238 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
239 }
240 module_exit(msr_exit)
241
242 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
243 MODULE_DESCRIPTION("x86 generic MSR driver");
244 MODULE_LICENSE("GPL");
245
