x86, msr: Export the register-setting MSR functions via /dev/*/msr

Make it possible to access the all-register-setting/getting MSR
functions via the MSR driver.  This is implemented as an ioctl() on
the standard MSR device node.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <petkovbb@gmail.com>

Documentation/ioctl/ioctl-number.txt

@@ -121,6 +121,7 @@ Code	Seq#	Include File		Comments
 'c'	00-7F	linux/comstats.h	conflict!
 'c'	00-7F	linux/coda.h		conflict!
 'c'	80-9F	arch/s390/include/asm/chsc.h
+'c'	A0-AF   arch/x86/include/asm/msr.h
 'd'	00-FF	linux/char/drm/drm/h	conflict!
 'd'	F0-FF	linux/digi1.h
 'e'	all	linux/digi1.h		conflict!

arch/x86/include/asm/msr.h

@@ -3,10 +3,16 @@
 
 #include <asm/msr-index.h>
 
-#ifdef __KERNEL__
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define X86_IOC_RDMSR_REGS	_IOWR('c', 0xA0, __u32[8])
+#define X86_IOC_WRMSR_REGS	_IOWR('c', 0xA1, __u32[8])
+
+#ifdef __KERNEL__
+
 #include <asm/asm.h>
 #include <asm/errno.h>
 #include <asm/cpumask.h>
@@ -286,6 +292,6 @@ static inline int wrmsr_safe_regs_on_cpu(unsigned int cpu, u32 regs[8])
 	return wrmsr_safe_regs(regs);
 }
 #endif  /* CONFIG_SMP */
-#endif /* __ASSEMBLY__ */
 #endif /* __KERNEL__ */
+#endif /* __ASSEMBLY__ */
 #endif /* _ASM_X86_MSR_H */

arch/x86/kernel/msr.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
@@ -121,6 +122,54 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
 	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 = iminor(file->f_path.dentry->d_inode);
@@ -151,6 +200,8 @@ static const struct file_operations msr_fops = {
 	.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)