msr.c

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/* ----------------------------------------------------------------------- *
 *
 *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
 *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
 *
 *   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 MSR access device
 *
 * This device is accessed by lseek() to the appropriate register number
 * and then read/write in chunks of 8 bytes.  A larger size means multiple
 * reads or writes of the same register.
 *
 * This driver uses /dev/cpu/%d/msr 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 *msr_class;

static loff_t msr_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 msr_read(struct file *file, char __user *buf,
            size_t count, loff_t *ppos)
{
    u32 __user *tmp = (u32 __user *) buf;
    u32 data[2];
    u32 reg = *ppos;
    int cpu = iminor(file->f_path.dentry->d_inode);
    int err = 0;
    ssize_t bytes = 0;

    if (count % 8)
        return -EINVAL; /* Invalid chunk size */

    for (; count; count -= 8) {
        err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
        if (err)
            break;
        if (copy_to_user(tmp, &data, 8)) {
            err = -EFAULT;
            break;
        }
        tmp += 2;
        bytes += 8;
    }

    return bytes ? bytes : err;
}

static ssize_t msr_write(struct file *file, const char __user *buf,
             size_t count, loff_t *ppos)
{
    const u32 __user *tmp = (const u32 __user *)buf;
    u32 data[2];
    u32 reg = *ppos;
    int cpu = iminor(file->f_path.dentry->d_inode);
    int err = 0;
    ssize_t bytes = 0;

    if (count % 8)
        return -EINVAL; /* Invalid chunk size */

    for (; count; count -= 8) {
        if (copy_from_user(&data, tmp, 8)) {
            err = -EFAULT;
            break;
        }
        err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
        if (err)
            break;
        tmp += 2;
        bytes += 8;
    }

    return bytes ? bytes : err;
}

static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
{
    u32 __user *uregs = (u32 __user *)arg;
    u32 regs[8];
    int cpu = iminor(file->f_path.dentry->d_inode);
    int err;

    switch (ioc) {
    case X86_IOC_RDMSR_REGS:
        if (!(file->f_mode & FMODE_READ)) {
            err = -EBADF;
            break;
        }
        if (copy_from_user(&regs, uregs, sizeof regs)) {
            err = -EFAULT;
            break;
        }
        err = rdmsr_safe_regs_on_cpu(cpu, regs);
        if (err)
            break;
        if (copy_to_user(uregs, &regs, sizeof regs))
            err = -EFAULT;
        break;

    case X86_IOC_WRMSR_REGS:
        if (!(file->f_mode & FMODE_WRITE)) {
            err = -EBADF;
            break;
        }
        if (copy_from_user(&regs, uregs, sizeof regs)) {
            err = -EFAULT;
            break;
        }
        err = wrmsr_safe_regs_on_cpu(cpu, regs);
        if (err)
            break;
        if (copy_to_user(uregs, &regs, sizeof regs))
            err = -EFAULT;
        break;

    default:
        err = -ENOTTY;
        break;
    }

    return err;
}

static int msr_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 (!cpu_has(c, X86_FEATURE_MSR))
        return -EIO;    /* MSR not supported */

    return 0;
}

/*
 * File operations we support
 */
static const struct file_operations msr_fops = {
    .owner = THIS_MODULE,
    .llseek = msr_seek,
    .read = msr_read,
    .write = msr_write,
    .open = msr_open,
    .unlocked_ioctl = msr_ioctl,
    .compat_ioctl = msr_ioctl,
};

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

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

static void msr_device_destroy(int cpu)
{
    device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
}

static int __cpuinit msr_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 = msr_device_create(cpu);
        break;
    case CPU_UP_CANCELED:
    case CPU_UP_CANCELED_FROZEN:
    case CPU_DEAD:
        msr_device_destroy(cpu);
        break;
    }
    return notifier_from_errno(err);
}

static struct notifier_block __refdata msr_class_cpu_notifier = {
    .notifier_call = msr_class_cpu_callback,
};

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

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

    if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
        printk(KERN_ERR "msr: unable to get major %d for msr\n",
               MSR_MAJOR);
        err = -EBUSY;
        goto out;
    }
    msr_class = class_create(THIS_MODULE, "msr");
    if (IS_ERR(msr_class)) {
        err = PTR_ERR(msr_class);
        goto out_chrdev;
    }
    msr_class->devnode = msr_devnode;
    get_online_cpus();
    for_each_online_cpu(i) {
        err = msr_device_create(i);
        if (err != 0)
            goto out_class;
    }
    register_hotcpu_notifier(&msr_class_cpu_notifier);
    put_online_cpus();

    err = 0;
    goto out;

out_class:
    i = 0;
    for_each_online_cpu(i)
        msr_device_destroy(i);
    put_online_cpus();
    class_destroy(msr_class);
out_chrdev:
    __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
out:
    return err;
}

static void __exit msr_exit(void)
{
    int cpu = 0;
    get_online_cpus();
    for_each_online_cpu(cpu)
        msr_device_destroy(cpu);
    class_destroy(msr_class);
    __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
    unregister_hotcpu_notifier(&msr_class_cpu_notifier);
    put_online_cpus();
}

module_init(msr_init);
module_exit(msr_exit)

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