1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* ----------------------------------------------------------------------- *
4 * Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
5 * Copyright 2009 Intel Corporation; author: H. Peter Anvin
7 * ----------------------------------------------------------------------- */
10 * x86 MSR access device
12 * This device is accessed by lseek() to the appropriate register number
13 * and then read/write in chunks of 8 bytes. A larger size means multiple
14 * reads or writes of the same register.
16 * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
17 * an SMP box will direct the access to CPU %d.
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
22 #include <linux/module.h>
24 #include <linux/types.h>
25 #include <linux/errno.h>
26 #include <linux/fcntl.h>
27 #include <linux/init.h>
28 #include <linux/poll.h>
29 #include <linux/smp.h>
30 #include <linux/major.h>
32 #include <linux/device.h>
33 #include <linux/cpu.h>
34 #include <linux/notifier.h>
35 #include <linux/uaccess.h>
36 #include <linux/gfp.h>
38 #include <asm/cpufeature.h>
41 static struct class *msr_class;
42 static enum cpuhp_state cpuhp_msr_state;
44 static ssize_t msr_read(struct file *file, char __user *buf,
45 size_t count, loff_t *ppos)
47 u32 __user *tmp = (u32 __user *) buf;
50 int cpu = iminor(file_inode(file));
55 return -EINVAL; /* Invalid chunk size */
57 for (; count; count -= 8) {
58 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
61 if (copy_to_user(tmp, &data, 8)) {
69 return bytes ? bytes : err;
72 static ssize_t msr_write(struct file *file, const char __user *buf,
73 size_t count, loff_t *ppos)
75 const u32 __user *tmp = (const u32 __user *)buf;
78 int cpu = iminor(file_inode(file));
83 return -EINVAL; /* Invalid chunk size */
85 for (; count; count -= 8) {
86 if (copy_from_user(&data, tmp, 8)) {
90 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
97 return bytes ? bytes : err;
100 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
102 u32 __user *uregs = (u32 __user *)arg;
104 int cpu = iminor(file_inode(file));
108 case X86_IOC_RDMSR_REGS:
109 if (!(file->f_mode & FMODE_READ)) {
113 if (copy_from_user(®s, uregs, sizeof(regs))) {
117 err = rdmsr_safe_regs_on_cpu(cpu, regs);
120 if (copy_to_user(uregs, ®s, sizeof(regs)))
124 case X86_IOC_WRMSR_REGS:
125 if (!(file->f_mode & FMODE_WRITE)) {
129 if (copy_from_user(®s, uregs, sizeof(regs))) {
133 err = wrmsr_safe_regs_on_cpu(cpu, regs);
136 if (copy_to_user(uregs, ®s, sizeof(regs)))
148 static int msr_open(struct inode *inode, struct file *file)
150 unsigned int cpu = iminor(file_inode(file));
151 struct cpuinfo_x86 *c;
153 if (!capable(CAP_SYS_RAWIO))
156 if (cpu >= nr_cpu_ids || !cpu_online(cpu))
157 return -ENXIO; /* No such CPU */
160 if (!cpu_has(c, X86_FEATURE_MSR))
161 return -EIO; /* MSR not supported */
167 * File operations we support
169 static const struct file_operations msr_fops = {
170 .owner = THIS_MODULE,
171 .llseek = no_seek_end_llseek,
175 .unlocked_ioctl = msr_ioctl,
176 .compat_ioctl = msr_ioctl,
179 static int msr_device_create(unsigned int cpu)
183 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
185 return PTR_ERR_OR_ZERO(dev);
188 static int msr_device_destroy(unsigned int cpu)
190 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
194 static char *msr_devnode(struct device *dev, umode_t *mode)
196 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
199 static int __init msr_init(void)
203 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
204 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
207 msr_class = class_create(THIS_MODULE, "msr");
208 if (IS_ERR(msr_class)) {
209 err = PTR_ERR(msr_class);
212 msr_class->devnode = msr_devnode;
214 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
215 msr_device_create, msr_device_destroy);
218 cpuhp_msr_state = err;
222 class_destroy(msr_class);
224 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
227 module_init(msr_init);
229 static void __exit msr_exit(void)
231 cpuhp_remove_state(cpuhp_msr_state);
232 class_destroy(msr_class);
233 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
235 module_exit(msr_exit)
237 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
238 MODULE_DESCRIPTION("x86 generic MSR driver");
239 MODULE_LICENSE("GPL");