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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 
39 #include <asm/processor.h>
40 #include <asm/msr.h>
41 #include <asm/uaccess.h>
42 #include <asm/system.h>
43 
44 static struct class *msr_class;
45 
msr_seek(struct file * file,loff_t offset,int orig)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 
msr_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)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 
msr_write(struct file * file,const char __user * buf,size_t count,loff_t * ppos)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 
msr_open(struct inode * inode,struct file * file)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 
msr_device_create(int cpu)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 
msr_device_destroy(int cpu)171 static void msr_device_destroy(int cpu)
172 {
173 	device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
174 }
175 
msr_class_cpu_callback(struct notifier_block * nfb,unsigned long action,void * hcpu)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 
msr_init(void)199 static int __init msr_init(void)
200 {
201 	int i, err = 0;
202 	i = 0;
203 
204 	if (register_chrdev(MSR_MAJOR, "cpu/msr", &msr_fops)) {
205 		printk(KERN_ERR "msr: unable to get major %d for msr\n",
206 		       MSR_MAJOR);
207 		err = -EBUSY;
208 		goto out;
209 	}
210 	msr_class = class_create(THIS_MODULE, "msr");
211 	if (IS_ERR(msr_class)) {
212 		err = PTR_ERR(msr_class);
213 		goto out_chrdev;
214 	}
215 	for_each_online_cpu(i) {
216 		err = msr_device_create(i);
217 		if (err != 0)
218 			goto out_class;
219 	}
220 	register_hotcpu_notifier(&msr_class_cpu_notifier);
221 
222 	err = 0;
223 	goto out;
224 
225 out_class:
226 	i = 0;
227 	for_each_online_cpu(i)
228 		msr_device_destroy(i);
229 	class_destroy(msr_class);
230 out_chrdev:
231 	unregister_chrdev(MSR_MAJOR, "cpu/msr");
232 out:
233 	return err;
234 }
235 
msr_exit(void)236 static void __exit msr_exit(void)
237 {
238 	int cpu = 0;
239 	for_each_online_cpu(cpu)
240 		msr_device_destroy(cpu);
241 	class_destroy(msr_class);
242 	unregister_chrdev(MSR_MAJOR, "cpu/msr");
243 	unregister_hotcpu_notifier(&msr_class_cpu_notifier);
244 }
245 
246 module_init(msr_init);
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");
252