xref: /openbmc/linux/arch/x86/kernel/msr.c (revision b34e08d5)
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 #include <linux/module.h>
26 
27 #include <linux/types.h>
28 #include <linux/errno.h>
29 #include <linux/fcntl.h>
30 #include <linux/init.h>
31 #include <linux/poll.h>
32 #include <linux/smp.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 #include <linux/gfp.h>
40 
41 #include <asm/processor.h>
42 #include <asm/msr.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_inode(file);
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_inode(file));
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 			break;
85 		if (copy_to_user(tmp, &data, 8)) {
86 			err = -EFAULT;
87 			break;
88 		}
89 		tmp += 2;
90 		bytes += 8;
91 	}
92 
93 	return bytes ? bytes : err;
94 }
95 
96 static ssize_t msr_write(struct file *file, const char __user *buf,
97 			 size_t count, loff_t *ppos)
98 {
99 	const u32 __user *tmp = (const u32 __user *)buf;
100 	u32 data[2];
101 	u32 reg = *ppos;
102 	int cpu = iminor(file_inode(file));
103 	int err = 0;
104 	ssize_t bytes = 0;
105 
106 	if (count % 8)
107 		return -EINVAL;	/* Invalid chunk size */
108 
109 	for (; count; count -= 8) {
110 		if (copy_from_user(&data, tmp, 8)) {
111 			err = -EFAULT;
112 			break;
113 		}
114 		err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
115 		if (err)
116 			break;
117 		tmp += 2;
118 		bytes += 8;
119 	}
120 
121 	return bytes ? bytes : err;
122 }
123 
124 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
125 {
126 	u32 __user *uregs = (u32 __user *)arg;
127 	u32 regs[8];
128 	int cpu = iminor(file_inode(file));
129 	int err;
130 
131 	switch (ioc) {
132 	case X86_IOC_RDMSR_REGS:
133 		if (!(file->f_mode & FMODE_READ)) {
134 			err = -EBADF;
135 			break;
136 		}
137 		if (copy_from_user(&regs, uregs, sizeof regs)) {
138 			err = -EFAULT;
139 			break;
140 		}
141 		err = rdmsr_safe_regs_on_cpu(cpu, regs);
142 		if (err)
143 			break;
144 		if (copy_to_user(uregs, &regs, sizeof regs))
145 			err = -EFAULT;
146 		break;
147 
148 	case X86_IOC_WRMSR_REGS:
149 		if (!(file->f_mode & FMODE_WRITE)) {
150 			err = -EBADF;
151 			break;
152 		}
153 		if (copy_from_user(&regs, uregs, sizeof regs)) {
154 			err = -EFAULT;
155 			break;
156 		}
157 		err = wrmsr_safe_regs_on_cpu(cpu, regs);
158 		if (err)
159 			break;
160 		if (copy_to_user(uregs, &regs, sizeof regs))
161 			err = -EFAULT;
162 		break;
163 
164 	default:
165 		err = -ENOTTY;
166 		break;
167 	}
168 
169 	return err;
170 }
171 
172 static int msr_open(struct inode *inode, struct file *file)
173 {
174 	unsigned int cpu = iminor(file_inode(file));
175 	struct cpuinfo_x86 *c;
176 
177 	if (!capable(CAP_SYS_RAWIO))
178 		return -EPERM;
179 
180 	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
181 		return -ENXIO;	/* No such CPU */
182 
183 	c = &cpu_data(cpu);
184 	if (!cpu_has(c, X86_FEATURE_MSR))
185 		return -EIO;	/* MSR not supported */
186 
187 	return 0;
188 }
189 
190 /*
191  * File operations we support
192  */
193 static const struct file_operations msr_fops = {
194 	.owner = THIS_MODULE,
195 	.llseek = msr_seek,
196 	.read = msr_read,
197 	.write = msr_write,
198 	.open = msr_open,
199 	.unlocked_ioctl = msr_ioctl,
200 	.compat_ioctl = msr_ioctl,
201 };
202 
203 static int msr_device_create(int cpu)
204 {
205 	struct device *dev;
206 
207 	dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
208 			    "msr%d", cpu);
209 	return IS_ERR(dev) ? PTR_ERR(dev) : 0;
210 }
211 
212 static void msr_device_destroy(int cpu)
213 {
214 	device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
215 }
216 
217 static int msr_class_cpu_callback(struct notifier_block *nfb,
218 				  unsigned long action, void *hcpu)
219 {
220 	unsigned int cpu = (unsigned long)hcpu;
221 	int err = 0;
222 
223 	switch (action) {
224 	case CPU_UP_PREPARE:
225 		err = msr_device_create(cpu);
226 		break;
227 	case CPU_UP_CANCELED:
228 	case CPU_UP_CANCELED_FROZEN:
229 	case CPU_DEAD:
230 		msr_device_destroy(cpu);
231 		break;
232 	}
233 	return notifier_from_errno(err);
234 }
235 
236 static struct notifier_block __refdata msr_class_cpu_notifier = {
237 	.notifier_call = msr_class_cpu_callback,
238 };
239 
240 static char *msr_devnode(struct device *dev, umode_t *mode)
241 {
242 	return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
243 }
244 
245 static int __init msr_init(void)
246 {
247 	int i, err = 0;
248 	i = 0;
249 
250 	if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
251 		printk(KERN_ERR "msr: unable to get major %d for msr\n",
252 		       MSR_MAJOR);
253 		err = -EBUSY;
254 		goto out;
255 	}
256 	msr_class = class_create(THIS_MODULE, "msr");
257 	if (IS_ERR(msr_class)) {
258 		err = PTR_ERR(msr_class);
259 		goto out_chrdev;
260 	}
261 	msr_class->devnode = msr_devnode;
262 
263 	cpu_notifier_register_begin();
264 	for_each_online_cpu(i) {
265 		err = msr_device_create(i);
266 		if (err != 0)
267 			goto out_class;
268 	}
269 	__register_hotcpu_notifier(&msr_class_cpu_notifier);
270 	cpu_notifier_register_done();
271 
272 	err = 0;
273 	goto out;
274 
275 out_class:
276 	i = 0;
277 	for_each_online_cpu(i)
278 		msr_device_destroy(i);
279 	cpu_notifier_register_done();
280 	class_destroy(msr_class);
281 out_chrdev:
282 	__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
283 out:
284 	return err;
285 }
286 
287 static void __exit msr_exit(void)
288 {
289 	int cpu = 0;
290 
291 	cpu_notifier_register_begin();
292 	for_each_online_cpu(cpu)
293 		msr_device_destroy(cpu);
294 	class_destroy(msr_class);
295 	__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
296 	__unregister_hotcpu_notifier(&msr_class_cpu_notifier);
297 	cpu_notifier_register_done();
298 }
299 
300 module_init(msr_init);
301 module_exit(msr_exit)
302 
303 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
304 MODULE_DESCRIPTION("x86 generic MSR driver");
305 MODULE_LICENSE("GPL");
306