linux/arch/x86_64/kernel/msr.c

/* ----------------------------------------------------------------------- *
 *   
 *   Copyright 2000 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.
 *
 * ----------------------------------------------------------------------- */

/*
 * msr.c
 *
 * 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/config.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/smp_lock.h>
#include <linux/major.h>
#include <linux/fs.h>

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

/* Note: "err" is handled in a funny way below.  Otherwise one version
   of gcc or another breaks. */

static inline int wrmsr_eio(u32 reg, u32 eax, u32 edx)
{
	int err;

	asm volatile ("1:	wrmsr\n"
		      "2:\n"
		      ".section .fixup,\"ax\"\n"
		      "3:	movl %4,%0\n"
		      "	jmp 2b\n"
		      ".previous\n"
		      ".section __ex_table,\"a\"\n"
		      "	.align 8\n" "	.quad 1b,3b\n" ".previous":"=&bDS" (err)
		      :"a"(eax), "d"(edx), "c"(reg), "i"(-EIO), "0"(0));

	return err;
}

static inline int rdmsr_eio(u32 reg, u32 *eax, u32 *edx)
{
	int err;

	asm volatile ("1:	rdmsr\n"
		      "2:\n"
		      ".section .fixup,\"ax\"\n"
		      "3:	movl %4,%0\n"
		      "	jmp 2b\n"
		      ".previous\n"
		      ".section __ex_table,\"a\"\n"
		      "	.align 8\n"
		      "	.quad 1b,3b\n"
		      ".previous":"=&bDS" (err), "=a"(*eax), "=d"(*edx)
		      :"c"(reg), "i"(-EIO), "0"(0));

	return err;
}

#ifdef CONFIG_SMP

struct msr_command {
	int cpu;
	int err;
	u32 reg;
	u32 data[2];
};

static void msr_smp_wrmsr(void *cmd_block)
{
	struct msr_command *cmd = (struct msr_command *)cmd_block;

	if (cmd->cpu == smp_processor_id())
		cmd->err = wrmsr_eio(cmd->reg, cmd->data[0], cmd->data[1]);
}

static void msr_smp_rdmsr(void *cmd_block)
{
	struct msr_command *cmd = (struct msr_command *)cmd_block;

	if (cmd->cpu == smp_processor_id())
		cmd->err = rdmsr_eio(cmd->reg, &cmd->data[0], &cmd->data[1]);
}

static inline int do_wrmsr(int cpu, u32 reg, u32 eax, u32 edx)
{
	struct msr_command cmd;
	int ret;

	preempt_disable();
	if (cpu == smp_processor_id()) {
		ret = wrmsr_eio(reg, eax, edx);
	} else {
		cmd.cpu = cpu;
		cmd.reg = reg;
		cmd.data[0] = eax;
		cmd.data[1] = edx;

		smp_call_function(msr_smp_wrmsr, &cmd, 1, 1);
		ret = cmd.err;
	}
	preempt_enable();
	return ret;
}

static inline int do_rdmsr(int cpu, u32 reg, u32 * eax, u32 * edx)
{
	struct msr_command cmd;
	int ret;

	preempt_disable();
	if (cpu == smp_processor_id()) {
		ret = rdmsr_eio(reg, eax, edx);
	} else {
		cmd.cpu = cpu;
		cmd.reg = reg;

		smp_call_function(msr_smp_rdmsr, &cmd, 1, 1);

		*eax = cmd.data[0];
		*edx = cmd.data[1];

		ret = cmd.err;
	}
	preempt_enable();
	return ret;
}

#else				/* ! CONFIG_SMP */

static inline int do_wrmsr(int cpu, u32 reg, u32 eax, u32 edx)
{
	return wrmsr_eio(reg, eax, edx);
}

static inline int do_rdmsr(int cpu, u32 reg, u32 *eax, u32 *edx)
{
	return rdmsr_eio(reg, eax, edx);
}

#endif				/* ! CONFIG_SMP */

static loff_t msr_seek(struct file *file, loff_t offset, int orig)
{
	loff_t ret = -EINVAL;

	lock_kernel();
	switch (orig) {
	case 0:
		file->f_pos = offset;
		ret = file->f_pos;
		break;
	case 1:
		file->f_pos += offset;
		ret = file->f_pos;
	}
	unlock_kernel();
	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];
	size_t rv;
	u32 reg = *ppos;
	int cpu = iminor(file->f_dentry->d_inode);
	int err;

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

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

	return ((char __user *)tmp) - buf;
}

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];
	size_t rv;
	u32 reg = *ppos;
	int cpu = iminor(file->f_dentry->d_inode);
	int err;

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

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

	return ((char __user *)tmp) - buf;
}

static int msr_open(struct inode *inode, struct file *file)
{
	unsigned int cpu = iminor(file->f_dentry->d_inode);
	struct cpuinfo_x86 *c = &(cpu_data)[cpu];

	if (cpu >= NR_CPUS || !cpu_online(cpu))
		return -ENXIO;	/* No such CPU */
	if (!cpu_has(c, X86_FEATURE_MSR))
		return -EIO;	/* MSR not supported */

	return 0;
}

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

static int __init msr_init(void)
{
	if (register_chrdev(MSR_MAJOR, "cpu/msr", &msr_fops)) {
		printk(KERN_ERR "msr: unable to get major %d for msr\n",
		       MSR_MAJOR);
		return -EBUSY;
	}

	return 0;
}

static void __exit msr_exit(void)
{
	unregister_chrdev(MSR_MAJOR, "cpu/msr");
}

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");