linux/arch/x86/kernel/msr.c
Srivatsa S. Bhat de82a01bef x86, msr: Fix CPU hotplug callback registration
Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();

Fix the msr code in x86 by using this latter form of callback registration.

Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-03-20 13:43:42 +01:00

306 lines
6.5 KiB
C

/* ----------------------------------------------------------------------- *
*
* 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_inode(file);
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_inode(file));
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_inode(file));
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_inode(file));
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 = iminor(file_inode(file));
struct cpuinfo_x86 *c;
if (!capable(CAP_SYS_RAWIO))
return -EPERM;
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 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 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;
cpu_notifier_register_begin();
for_each_online_cpu(i) {
err = msr_device_create(i);
if (err != 0)
goto out_class;
}
__register_hotcpu_notifier(&msr_class_cpu_notifier);
cpu_notifier_register_done();
err = 0;
goto out;
out_class:
i = 0;
for_each_online_cpu(i)
msr_device_destroy(i);
cpu_notifier_register_done();
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;
cpu_notifier_register_begin();
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);
cpu_notifier_register_done();
}
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");