LXR linux/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
  43static struct class *cpuid_class;
  44static enum cpuhp_state cpuhp_cpuid_state;
  45
  46struct cpuid_regs_done {
  47        struct cpuid_regs regs;
  48        struct completion done;
  49};
  50
  51static 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
  62static 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
 102static 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 */
 121static 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
 128static 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
 137static int cpuid_device_destroy(unsigned int cpu)
 138{
 139        device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu));
 140        return 0;
 141}
 142
 143static char *cpuid_devnode(struct device *dev, umode_t *mode)
 144{
 145        return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
 146}
 147
 148static 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
 173out_class:
 174        class_destroy(cpuid_class);
 175out_chrdev:
 176        __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
 177        return err;
 178}
 179module_init(cpuid_init);
 180
 181static 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}
 187module_exit(cpuid_exit);
 188
 189MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
 190MODULE_DESCRIPTION("x86 generic CPUID driver");
 191MODULE_LICENSE("GPL");
 192