xref: /openbmc/linux/arch/x86/kernel/msr.c (revision 545e4006)
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 
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;
76 
77 	if (count % 8)
78 		return -EINVAL;	/* Invalid chunk size */
79 
80 	for (; count; count -= 8) {
81 		err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
82 		if (err)
83 			return -EIO;
84 		if (copy_to_user(tmp, &data, 8))
85 			return -EFAULT;
86 		tmp += 2;
87 	}
88 
89 	return ((char __user *)tmp) - buf;
90 }
91 
92 static ssize_t msr_write(struct file *file, const char __user *buf,
93 			 size_t count, loff_t *ppos)
94 {
95 	const u32 __user *tmp = (const u32 __user *)buf;
96 	u32 data[2];
97 	u32 reg = *ppos;
98 	int cpu = iminor(file->f_path.dentry->d_inode);
99 	int err;
100 
101 	if (count % 8)
102 		return -EINVAL;	/* Invalid chunk size */
103 
104 	for (; count; count -= 8) {
105 		if (copy_from_user(&data, tmp, 8))
106 			return -EFAULT;
107 		err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
108 		if (err)
109 			return -EIO;
110 		tmp += 2;
111 	}
112 
113 	return ((char __user *)tmp) - buf;
114 }
115 
116 static int msr_open(struct inode *inode, struct file *file)
117 {
118 	unsigned int cpu = iminor(file->f_path.dentry->d_inode);
119 	struct cpuinfo_x86 *c = &cpu_data(cpu);
120 	int ret = 0;
121 
122 	lock_kernel();
123 	cpu = iminor(file->f_path.dentry->d_inode);
124 
125 	if (cpu >= NR_CPUS || !cpu_online(cpu)) {
126 		ret = -ENXIO;	/* No such CPU */
127 		goto out;
128 	}
129 	c = &cpu_data(cpu);
130 	if (!cpu_has(c, X86_FEATURE_MSR))
131 		ret = -EIO;	/* MSR not supported */
132 out:
133 	unlock_kernel();
134 	return 0;
135 }
136 
137 /*
138  * File operations we support
139  */
140 static const struct file_operations msr_fops = {
141 	.owner = THIS_MODULE,
142 	.llseek = msr_seek,
143 	.read = msr_read,
144 	.write = msr_write,
145 	.open = msr_open,
146 };
147 
148 static int __cpuinit msr_device_create(int cpu)
149 {
150 	struct device *dev;
151 
152 	dev = device_create_drvdata(msr_class, NULL, MKDEV(MSR_MAJOR, cpu),
153 				    NULL, "msr%d", cpu);
154 	return IS_ERR(dev) ? PTR_ERR(dev) : 0;
155 }
156 
157 static void msr_device_destroy(int cpu)
158 {
159 	device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
160 }
161 
162 static int __cpuinit msr_class_cpu_callback(struct notifier_block *nfb,
163 				unsigned long action, void *hcpu)
164 {
165 	unsigned int cpu = (unsigned long)hcpu;
166 	int err = 0;
167 
168 	switch (action) {
169 	case CPU_UP_PREPARE:
170 		err = msr_device_create(cpu);
171 		break;
172 	case CPU_UP_CANCELED:
173 	case CPU_UP_CANCELED_FROZEN:
174 	case CPU_DEAD:
175 		msr_device_destroy(cpu);
176 		break;
177 	}
178 	return err ? NOTIFY_BAD : NOTIFY_OK;
179 }
180 
181 static struct notifier_block __refdata msr_class_cpu_notifier = {
182 	.notifier_call = msr_class_cpu_callback,
183 };
184 
185 static int __init msr_init(void)
186 {
187 	int i, err = 0;
188 	i = 0;
189 
190 	if (register_chrdev(MSR_MAJOR, "cpu/msr", &msr_fops)) {
191 		printk(KERN_ERR "msr: unable to get major %d for msr\n",
192 		       MSR_MAJOR);
193 		err = -EBUSY;
194 		goto out;
195 	}
196 	msr_class = class_create(THIS_MODULE, "msr");
197 	if (IS_ERR(msr_class)) {
198 		err = PTR_ERR(msr_class);
199 		goto out_chrdev;
200 	}
201 	for_each_online_cpu(i) {
202 		err = msr_device_create(i);
203 		if (err != 0)
204 			goto out_class;
205 	}
206 	register_hotcpu_notifier(&msr_class_cpu_notifier);
207 
208 	err = 0;
209 	goto out;
210 
211 out_class:
212 	i = 0;
213 	for_each_online_cpu(i)
214 		msr_device_destroy(i);
215 	class_destroy(msr_class);
216 out_chrdev:
217 	unregister_chrdev(MSR_MAJOR, "cpu/msr");
218 out:
219 	return err;
220 }
221 
222 static void __exit msr_exit(void)
223 {
224 	int cpu = 0;
225 	for_each_online_cpu(cpu)
226 		msr_device_destroy(cpu);
227 	class_destroy(msr_class);
228 	unregister_chrdev(MSR_MAJOR, "cpu/msr");
229 	unregister_hotcpu_notifier(&msr_class_cpu_notifier);
230 }
231 
232 module_init(msr_init);
233 module_exit(msr_exit)
234 
235 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
236 MODULE_DESCRIPTION("x86 generic MSR driver");
237 MODULE_LICENSE("GPL");
238