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 enum cpuhp_state cpuhp_cpuid_state; 44 45 struct cpuid_regs_done { 46 struct cpuid_regs regs; 47 struct completion done; 48 }; 49 50 static void cpuid_smp_cpuid(void *cmd_block) 51 { 52 struct cpuid_regs_done *cmd = cmd_block; 53 54 cpuid_count(cmd->regs.eax, cmd->regs.ecx, 55 &cmd->regs.eax, &cmd->regs.ebx, 56 &cmd->regs.ecx, &cmd->regs.edx); 57 58 complete(&cmd->done); 59 } 60 61 static ssize_t cpuid_read(struct file *file, char __user *buf, 62 size_t count, loff_t *ppos) 63 { 64 char __user *tmp = buf; 65 struct cpuid_regs_done cmd; 66 int cpu = iminor(file_inode(file)); 67 u64 pos = *ppos; 68 ssize_t bytes = 0; 69 int err = 0; 70 71 if (count % 16) 72 return -EINVAL; /* Invalid chunk size */ 73 74 init_completion(&cmd.done); 75 for (; count; count -= 16) { 76 call_single_data_t csd; 77 78 INIT_CSD(&csd, cpuid_smp_cpuid, &cmd); 79 80 cmd.regs.eax = pos; 81 cmd.regs.ecx = pos >> 32; 82 83 err = smp_call_function_single_async(cpu, &csd); 84 if (err) 85 break; 86 wait_for_completion(&cmd.done); 87 if (copy_to_user(tmp, &cmd.regs, 16)) { 88 err = -EFAULT; 89 break; 90 } 91 tmp += 16; 92 bytes += 16; 93 *ppos = ++pos; 94 reinit_completion(&cmd.done); 95 } 96 97 return bytes ? bytes : err; 98 } 99 100 static int cpuid_open(struct inode *inode, struct file *file) 101 { 102 unsigned int cpu; 103 struct cpuinfo_x86 *c; 104 105 cpu = iminor(file_inode(file)); 106 if (cpu >= nr_cpu_ids || !cpu_online(cpu)) 107 return -ENXIO; /* No such CPU */ 108 109 c = &cpu_data(cpu); 110 if (c->cpuid_level < 0) 111 return -EIO; /* CPUID not supported */ 112 113 return 0; 114 } 115 116 /* 117 * File operations we support 118 */ 119 static const struct file_operations cpuid_fops = { 120 .owner = THIS_MODULE, 121 .llseek = no_seek_end_llseek, 122 .read = cpuid_read, 123 .open = cpuid_open, 124 }; 125 126 static char *cpuid_devnode(const struct device *dev, umode_t *mode) 127 { 128 return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt)); 129 } 130 131 static const struct class cpuid_class = { 132 .name = "cpuid", 133 .devnode = cpuid_devnode, 134 }; 135 136 static int cpuid_device_create(unsigned int cpu) 137 { 138 struct device *dev; 139 140 dev = device_create(&cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL, 141 "cpu%d", cpu); 142 return PTR_ERR_OR_ZERO(dev); 143 } 144 145 static int cpuid_device_destroy(unsigned int cpu) 146 { 147 device_destroy(&cpuid_class, MKDEV(CPUID_MAJOR, cpu)); 148 return 0; 149 } 150 151 static int __init cpuid_init(void) 152 { 153 int err; 154 155 if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS, 156 "cpu/cpuid", &cpuid_fops)) { 157 printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n", 158 CPUID_MAJOR); 159 return -EBUSY; 160 } 161 err = class_register(&cpuid_class); 162 if (err) 163 goto out_chrdev; 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_unregister(&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_unregister(&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