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
  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
 101static 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 */
 120static 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
 127static 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
 136static int cpuid_device_destroy(unsigned int cpu)
 137{
 138        device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu));
 139        return 0;
 140}
 141
 142static char *cpuid_devnode(struct device *dev, umode_t *mode)
 143{
 144        return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
 145}
 146
 147static 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
 172out_class:
 173        class_destroy(cpuid_class);
 174out_chrdev:
 175        __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
 176        return err;
 177}
 178module_init(cpuid_init);
 179
 180static 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}
 186module_exit(cpuid_exit);
 187
 188MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
 189MODULE_DESCRIPTION("x86 generic CPUID driver");
 190MODULE_LICENSE("GPL");
 191