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 79 INIT_CSD(&csd, cpuid_smp_cpuid, &cmd); 80 81 cmd.regs.eax = pos; 82 cmd.regs.ecx = pos >> 32; 83 84 err = smp_call_function_single_async(cpu, &csd); 85 if (err) 86 break; 87 wait_for_completion(&cmd.done); 88 if (copy_to_user(tmp, &cmd.regs, 16)) { 89 err = -EFAULT; 90 break; 91 } 92 tmp += 16; 93 bytes += 16; 94 *ppos = ++pos; 95 reinit_completion(&cmd.done); 96 } 97 98 return bytes ? bytes : err; 99 } 100 101 static int cpuid_open(struct inode *inode, struct file *file) 102 { 103 unsigned int cpu; 104 struct cpuinfo_x86 *c; 105 106 cpu = iminor(file_inode(file)); 107 if (cpu >= nr_cpu_ids || !cpu_online(cpu)) 108 return -ENXIO; /* No such CPU */ 109 110 c = &cpu_data(cpu); 111 if (c->cpuid_level < 0) 112 return -EIO; /* CPUID not supported */ 113 114 return 0; 115 } 116 117 /* 118 * File operations we support 119 */ 120 static const struct file_operations cpuid_fops = { 121 .owner = THIS_MODULE, 122 .llseek = no_seek_end_llseek, 123 .read = cpuid_read, 124 .open = cpuid_open, 125 }; 126 127 static int cpuid_device_create(unsigned int cpu) 128 { 129 struct device *dev; 130 131 dev = device_create(cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL, 132 "cpu%d", cpu); 133 return PTR_ERR_OR_ZERO(dev); 134 } 135 136 static int cpuid_device_destroy(unsigned int cpu) 137 { 138 device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu)); 139 return 0; 140 } 141 142 static char *cpuid_devnode(const struct device *dev, umode_t *mode) 143 { 144 return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt)); 145 } 146 147 static int __init cpuid_init(void) 148 { 149 int err; 150 151 if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS, 152 "cpu/cpuid", &cpuid_fops)) { 153 printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n", 154 CPUID_MAJOR); 155 return -EBUSY; 156 } 157 cpuid_class = class_create(THIS_MODULE, "cpuid"); 158 if (IS_ERR(cpuid_class)) { 159 err = PTR_ERR(cpuid_class); 160 goto out_chrdev; 161 } 162 cpuid_class->devnode = cpuid_devnode; 163 164 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/cpuid:online", 165 cpuid_device_create, cpuid_device_destroy); 166 if (err < 0) 167 goto out_class; 168 169 cpuhp_cpuid_state = err; 170 return 0; 171 172 out_class: 173 class_destroy(cpuid_class); 174 out_chrdev: 175 __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); 176 return err; 177 } 178 module_init(cpuid_init); 179 180 static void __exit cpuid_exit(void) 181 { 182 cpuhp_remove_state(cpuhp_cpuid_state); 183 class_destroy(cpuid_class); 184 __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); 185 } 186 module_exit(cpuid_exit); 187 188 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>"); 189 MODULE_DESCRIPTION("x86 generic CPUID driver"); 190 MODULE_LICENSE("GPL"); 191