[RFC][PATCH 6/12 not tested yet] PPC: introduce copy_in_user() for 32-bit

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

During the work of KVM's dirty page logging optimization, we encountered
the need of copy_in_user() for 32-bit ppc and x86: these will be used for
manipulating dirty bitmaps in user space.

So we implement copy_in_user() for 32-bit with __copy_tofrom_user().

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
CC: Alexander Graf <agraf@suse.de>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/uaccess.h |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index bd0fb84..3a01ce8 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -359,6 +359,23 @@ static inline unsigned long copy_to_user(void __user *to,
 	return n;
 }
 
+static inline unsigned long copy_in_user(void __user *to,
+		const void __user *from, unsigned long n)
+{
+	unsigned long over;
+
+	if (likely(access_ok(VERIFY_READ, from, n) &&
+	    access_ok(VERIFY_WRITE, to, n)))
+		return __copy_tofrom_user(to, from, n);
+	if (((unsigned long)from < TASK_SIZE) ||
+	    ((unsigned long)to < TASK_SIZE)) {
+		over = max((unsigned long)from, (unsigned long)to)
+			+ n - TASK_SIZE;
+		return __copy_tofrom_user(to, from, n - over) + over;
+	}
+	return n;
+}
+
 #else /* __powerpc64__ */
 
 #define __copy_in_user(to, from, size) \
-- 
1.7.0.4