cpuid.c

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/* ----------------------------------------------------------------------- *
 *
 *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
 *   USA; either version 2 of the License, or (at your option) any later
 *   version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * x86 CPUID access device
 *
 * This device is accessed by lseek() to the appropriate CPUID level
 * and then read in chunks of 16 bytes.  A larger size means multiple
 * reads of consecutive levels.
 *
 * The lower 32 bits of the file position is used as the incoming %eax,
 * and the upper 32 bits of the file position as the incoming %ecx,
 * the latter intended for "counting" eax levels like eax=4.
 *
 * This driver uses /dev/cpu/%d/cpuid where %d is the minor number, and on
 * an SMP box will direct the access to CPU %d.
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/smp.h>
#include <linux/major.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/uaccess.h>
#include <linux/gfp.h>

#include <asm/processor.h>
#include <asm/msr.h>

static struct class *cpuid_class;

struct cpuid_regs {
    u32 eax, ebx, ecx, edx;
};

static void cpuid_smp_cpuid(void *cmd_block)
{
    struct cpuid_regs *cmd = (struct cpuid_regs *)cmd_block;

    cpuid_count(cmd->eax, cmd->ecx,
            &cmd->eax, &cmd->ebx, &cmd->ecx, &cmd->edx);
}

static loff_t cpuid_seek(struct file *file, loff_t offset, int orig)
{
    loff_t ret;
    struct inode *inode = file->f_mapping->host;

    mutex_lock(&inode->i_mutex);
    switch (orig) {
    case 0:
        file->f_pos = offset;
        ret = file->f_pos;
        break;
    case 1:
        file->f_pos += offset;
        ret = file->f_pos;
        break;
    default:
        ret = -EINVAL;
    }
    mutex_unlock(&inode->i_mutex);
    return ret;
}

static ssize_t cpuid_read(struct file *file, char __user *buf,
              size_t count, loff_t *ppos)
{
    char __user *tmp = buf;
    struct cpuid_regs cmd;
    int cpu = iminor(file->f_path.dentry->d_inode);
    u64 pos = *ppos;
    ssize_t bytes = 0;
    int err = 0;

    if (count % 16)
        return -EINVAL; /* Invalid chunk size */

    for (; count; count -= 16) {
        cmd.eax = pos;
        cmd.ecx = pos >> 32;
        err = smp_call_function_single(cpu, cpuid_smp_cpuid, &cmd, 1);
        if (err)
            break;
        if (copy_to_user(tmp, &cmd, 16)) {
            err = -EFAULT;
            break;
        }
        tmp += 16;
        bytes += 16;
        *ppos = ++pos;
    }

    return bytes ? bytes : err;
}

static int cpuid_open(struct inode *inode, struct file *file)
{
    unsigned int cpu;
    struct cpuinfo_x86 *c;

    cpu = iminor(file->f_path.dentry->d_inode);
    if (cpu >= nr_cpu_ids || !cpu_online(cpu))
        return -ENXIO;  /* No such CPU */

    c = &cpu_data(cpu);
    if (c->cpuid_level < 0)
        return -EIO;    /* CPUID not supported */

    return 0;
}

/*
 * File operations we support
 */
static const struct file_operations cpuid_fops = {
    .owner = THIS_MODULE,
    .llseek = cpuid_seek,
    .read = cpuid_read,
    .open = cpuid_open,
};

static __cpuinit int cpuid_device_create(int cpu)
{
    struct device *dev;

    dev = device_create(cpuid_class, NULL, MKDEV(CPUID_MAJOR, cpu), NULL,
                "cpu%d", cpu);
    return IS_ERR(dev) ? PTR_ERR(dev) : 0;
}

static void cpuid_device_destroy(int cpu)
{
    device_destroy(cpuid_class, MKDEV(CPUID_MAJOR, cpu));
}

static int __cpuinit cpuid_class_cpu_callback(struct notifier_block *nfb,
                          unsigned long action,
                          void *hcpu)
{
    unsigned int cpu = (unsigned long)hcpu;
    int err = 0;

    switch (action) {
    case CPU_UP_PREPARE:
        err = cpuid_device_create(cpu);
        break;
    case CPU_UP_CANCELED:
    case CPU_UP_CANCELED_FROZEN:
    case CPU_DEAD:
        cpuid_device_destroy(cpu);
        break;
    }
    return notifier_from_errno(err);
}

static struct notifier_block __refdata cpuid_class_cpu_notifier =
{
    .notifier_call = cpuid_class_cpu_callback,
};

static char *cpuid_devnode(struct device *dev, umode_t *mode)
{
    return kasprintf(GFP_KERNEL, "cpu/%u/cpuid", MINOR(dev->devt));
}

static int __init cpuid_init(void)
{
    int i, err = 0;
    i = 0;

    if (__register_chrdev(CPUID_MAJOR, 0, NR_CPUS,
                  "cpu/cpuid", &cpuid_fops)) {
        printk(KERN_ERR "cpuid: unable to get major %d for cpuid\n",
               CPUID_MAJOR);
        err = -EBUSY;
        goto out;
    }
    cpuid_class = class_create(THIS_MODULE, "cpuid");
    if (IS_ERR(cpuid_class)) {
        err = PTR_ERR(cpuid_class);
        goto out_chrdev;
    }
    cpuid_class->devnode = cpuid_devnode;
    get_online_cpus();
    for_each_online_cpu(i) {
        err = cpuid_device_create(i);
        if (err != 0)
            goto out_class;
    }
    register_hotcpu_notifier(&cpuid_class_cpu_notifier);
    put_online_cpus();

    err = 0;
    goto out;

out_class:
    i = 0;
    for_each_online_cpu(i) {
        cpuid_device_destroy(i);
    }
    put_online_cpus();
    class_destroy(cpuid_class);
out_chrdev:
    __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
out:
    return err;
}

static void __exit cpuid_exit(void)
{
    int cpu = 0;

    get_online_cpus();
    for_each_online_cpu(cpu)
        cpuid_device_destroy(cpu);
    class_destroy(cpuid_class);
    __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
    unregister_hotcpu_notifier(&cpuid_class_cpu_notifier);
    put_online_cpus();
}

module_init(cpuid_init);
module_exit(cpuid_exit);

MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
MODULE_DESCRIPTION("x86 generic CPUID driver");
MODULE_LICENSE("GPL");