arch/x86/kernel/cpuid.c

   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(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");