1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* ----------------------------------------------------------------------- * 3 * 4 * Copyright 2000-2008 H. Peter Anvin - All Rights Reserved 5 * 6 * ----------------------------------------------------------------------- */ 7 8 /* 9 * x86 CPUID access device 10 * 11 * This device is accessed by lseek() to the appropriate CPUID level 12 * and then read in chunks of 16 bytes. A larger size means multiple 13 * reads of consecutive levels. 14 * 15 * The lower 32 bits of the file position is used as the incoming %eax, 16 * and the upper 32 bits of the file position as the incoming %ecx, 17 * the latter intended for "counting" eax levels like eax=4. 18 * 19 * This driver uses /dev/cpu/%d/cpuid where %d is the minor number, and on 20 * an SMP box will direct the access to CPU %d. 21 */ 22 23 #include <linux/module.h> 24 25 #include <linux/types.h> 26 #include <linux/errno.h> 27 #include <linux/fcntl.h> 28 #include <linux/init.h> 29 #include <linux/poll.h> 30 #include <linux/smp.h> 31 #include <linux/major.h> 32 #include <linux/fs.h> 33 #include <linux/device.h> 34 #include <linux/cpu.h> 35 #include <linux/notifier.h> 36 #include <linux/uaccess.h> 37 #include <linux/gfp.h> 38 #include <linux/completion.h> 39 40 #include <asm/processor.h> 41 #include <asm/msr.h> 42 43 static struct class *cpuid_class; 44 static enum cpuhp_state cpuhp_cpuid_state; 45 46 struct cpuid_regs_done { 47 struct cpuid_regs regs; 48 struct completion done; 49 }; 50 51 static void cpuid_smp_cpuid(void *cmd_block) 52 { 53 struct cpuid_regs_done *cmd = cmd_block; 54 55 cpuid_count(cmd->regs.eax, cmd->regs.ecx, 56 &cmd->regs.eax, &cmd->regs.ebx, 57 &cmd->regs.ecx, &cmd->regs.edx); 58 59 complete(&cmd->done); 60 } 61 62 static ssize_t cpuid_read(struct file *file, char __user *buf, 63 size_t count, loff_t *ppos) 64 { 65 char __user *tmp = buf; 66 struct cpuid_regs_done cmd; 67 int cpu = iminor(file_inode(file)); 68 u64 pos = *ppos; 69 ssize_t bytes = 0; 70 int err = 0; 71 72 if (count % 16) 73 return -EINVAL; /* Invalid chunk size */ 74 75 init_completion(&cmd.done); 76 for (; count; count -= 16) { 77 call_single_data_t csd = { 78 .func = cpuid_smp_cpuid, 79 .info = &cmd, 80 }; 81 82 cmd.regs.eax = pos; 83 cmd.regs.ecx = pos >> 32; 84 85 err = smp_call_function_single_async(cpu, &csd); 86 if (err) 87 break; 88 wait_for_completion(&cmd.done); 89 if (copy_to_user(tmp, &cmd.regs, 16)) { 90 err = -EFAULT; 91 break; 92 } 93 tmp += 16; 94 bytes += 16; 95 *ppos = ++pos; 96 reinit_completion(&cmd.done); 97 } 98 99 return bytes ? bytes : err; 100 } 101 102 static int cpuid_open(struct inode *inode, struct file *file) 103 { 104 unsigned int cpu; 105 struct cpuinfo_x86 *c; 106 107 cpu = iminor(file_inode(file)); 108 if (cpu >= nr_cpu_ids || !cpu_online(cpu)) 109 return -ENXIO; /* No such CPU */ 110 111 c = &cpu_data(cpu); 112 if (c->cpuid_level < 0) 113 return -EIO; /* CPUID not supported */ 114 115 return 0; 116 } 117 118 /* 119 * File operations we support 120 */ 121 static const struct file_operations cpuid_fops = { 122 .owner = THIS_MODULE, 123 .llseek = no_seek_end_llseek, 124 .read = cpuid_read, 125 .open = cpuid_open, 126 }; 127 128 static int cpuid_device_create(unsigned int cpu) 129 { 130 struct device *dev; 131 132 dev = device_create(cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL, 133 "cpu%d", cpu); 134 return PTR_ERR_OR_ZERO(dev); 135 } 136 137 static int cpuid_device_destroy(unsigned int cpu) 138 { 139 device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu)); 140 return 0; 141 } 142 143 static char *cpuid_devnode(struct device *dev, umode_t *mode) 144 { 145 return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt)); 146 } 147 148 static int __init cpuid_init(void) 149 { 150 int err; 151 152 if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS, 153 "cpu/cpuid", &cpuid_fops)) { 154 printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n", 155 CPUID_MAJOR); 156 return -EBUSY; 157 } 158 cpuid_class = class_create(THIS_MODULE, "cpuid"); 159 if (IS_ERR(cpuid_class)) { 160 err = PTR_ERR(cpuid_class); 161 goto out_chrdev; 162 } 163 cpuid_class->devnode = cpuid_devnode; 164 165 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/cpuid:online", 166 cpuid_device_create, cpuid_device_destroy); 167 if (err < 0) 168 goto out_class; 169 170 cpuhp_cpuid_state = err; 171 return 0; 172 173 out_class: 174 class_destroy(cpuid_class); 175 out_chrdev: 176 __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); 177 return err; 178 } 179 module_init(cpuid_init); 180 181 static void __exit cpuid_exit(void) 182 { 183 cpuhp_remove_state(cpuhp_cpuid_state); 184 class_destroy(cpuid_class); 185 __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); 186 } 187 module_exit(cpuid_exit); 188 189 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>"); 190 MODULE_DESCRIPTION("x86 generic CPUID driver"); 191 MODULE_LICENSE("GPL"); 192