1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* ----------------------------------------------------------------------- * 3 * 4 * Copyright 2000-2008 H. Peter Anvin - All Rights Reserved 5 * Copyright 2009 Intel Corporation; author: H. Peter Anvin 6 * 7 * ----------------------------------------------------------------------- */ 8 9 /* 10 * x86 MSR access device 11 * 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. 15 * 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. 18 */ 19 20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 21 22 #include <linux/module.h> 23 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> 31 #include <linux/fs.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> 37 38 #include <asm/cpufeature.h> 39 #include <asm/msr.h> 40 41 static struct class *msr_class; 42 static enum cpuhp_state cpuhp_msr_state; 43 44 static ssize_t msr_read(struct file *file, char __user *buf, 45 size_t count, loff_t *ppos) 46 { 47 u32 __user *tmp = (u32 __user *) buf; 48 u32 data[2]; 49 u32 reg = *ppos; 50 int cpu = iminor(file_inode(file)); 51 int err = 0; 52 ssize_t bytes = 0; 53 54 if (count % 8) 55 return -EINVAL; /* Invalid chunk size */ 56 57 for (; count; count -= 8) { 58 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]); 59 if (err) 60 break; 61 if (copy_to_user(tmp, &data, 8)) { 62 err = -EFAULT; 63 break; 64 } 65 tmp += 2; 66 bytes += 8; 67 } 68 69 return bytes ? bytes : err; 70 } 71 72 static ssize_t msr_write(struct file *file, const char __user *buf, 73 size_t count, loff_t *ppos) 74 { 75 const u32 __user *tmp = (const u32 __user *)buf; 76 u32 data[2]; 77 u32 reg = *ppos; 78 int cpu = iminor(file_inode(file)); 79 int err = 0; 80 ssize_t bytes = 0; 81 82 if (count % 8) 83 return -EINVAL; /* Invalid chunk size */ 84 85 for (; count; count -= 8) { 86 if (copy_from_user(&data, tmp, 8)) { 87 err = -EFAULT; 88 break; 89 } 90 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]); 91 if (err) 92 break; 93 tmp += 2; 94 bytes += 8; 95 } 96 97 return bytes ? bytes : err; 98 } 99 100 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) 101 { 102 u32 __user *uregs = (u32 __user *)arg; 103 u32 regs[8]; 104 int cpu = iminor(file_inode(file)); 105 int err; 106 107 switch (ioc) { 108 case X86_IOC_RDMSR_REGS: 109 if (!(file->f_mode & FMODE_READ)) { 110 err = -EBADF; 111 break; 112 } 113 if (copy_from_user(®s, uregs, sizeof(regs))) { 114 err = -EFAULT; 115 break; 116 } 117 err = rdmsr_safe_regs_on_cpu(cpu, regs); 118 if (err) 119 break; 120 if (copy_to_user(uregs, ®s, sizeof(regs))) 121 err = -EFAULT; 122 break; 123 124 case X86_IOC_WRMSR_REGS: 125 if (!(file->f_mode & FMODE_WRITE)) { 126 err = -EBADF; 127 break; 128 } 129 if (copy_from_user(®s, uregs, sizeof(regs))) { 130 err = -EFAULT; 131 break; 132 } 133 err = wrmsr_safe_regs_on_cpu(cpu, regs); 134 if (err) 135 break; 136 if (copy_to_user(uregs, ®s, sizeof(regs))) 137 err = -EFAULT; 138 break; 139 140 default: 141 err = -ENOTTY; 142 break; 143 } 144 145 return err; 146 } 147 148 static int msr_open(struct inode *inode, struct file *file) 149 { 150 unsigned int cpu = iminor(file_inode(file)); 151 struct cpuinfo_x86 *c; 152 153 if (!capable(CAP_SYS_RAWIO)) 154 return -EPERM; 155 156 if (cpu >= nr_cpu_ids || !cpu_online(cpu)) 157 return -ENXIO; /* No such CPU */ 158 159 c = &cpu_data(cpu); 160 if (!cpu_has(c, X86_FEATURE_MSR)) 161 return -EIO; /* MSR not supported */ 162 163 return 0; 164 } 165 166 /* 167 * File operations we support 168 */ 169 static const struct file_operations msr_fops = { 170 .owner = THIS_MODULE, 171 .llseek = no_seek_end_llseek, 172 .read = msr_read, 173 .write = msr_write, 174 .open = msr_open, 175 .unlocked_ioctl = msr_ioctl, 176 .compat_ioctl = msr_ioctl, 177 }; 178 179 static int msr_device_create(unsigned int cpu) 180 { 181 struct device *dev; 182 183 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL, 184 "msr%d", cpu); 185 return PTR_ERR_OR_ZERO(dev); 186 } 187 188 static int msr_device_destroy(unsigned int cpu) 189 { 190 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu)); 191 return 0; 192 } 193 194 static char *msr_devnode(struct device *dev, umode_t *mode) 195 { 196 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt)); 197 } 198 199 static int __init msr_init(void) 200 { 201 int err; 202 203 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); 205 return -EBUSY; 206 } 207 msr_class = class_create(THIS_MODULE, "msr"); 208 if (IS_ERR(msr_class)) { 209 err = PTR_ERR(msr_class); 210 goto out_chrdev; 211 } 212 msr_class->devnode = msr_devnode; 213 214 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online", 215 msr_device_create, msr_device_destroy); 216 if (err < 0) 217 goto out_class; 218 cpuhp_msr_state = err; 219 return 0; 220 221 out_class: 222 class_destroy(msr_class); 223 out_chrdev: 224 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); 225 return err; 226 } 227 module_init(msr_init); 228 229 static void __exit msr_exit(void) 230 { 231 cpuhp_remove_state(cpuhp_msr_state); 232 class_destroy(msr_class); 233 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); 234 } 235 module_exit(msr_exit) 236 237 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>"); 238 MODULE_DESCRIPTION("x86 generic MSR driver"); 239 MODULE_LICENSE("GPL"); 240