linux-kernel - [tip:x86/uaccess] x86: Add 1/2/4/ 8 byte optimization to 64bit __copy_{from,to}_user

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Message-ID: <tip-ff47ab4ff3cddfa7bc1b25b990e24abe2ae474ff@git.kernel.org>
Date:	Tue, 10 Sep 2013 16:30:41 -0700
From:	tip-bot for Andi Kleen <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	ak@...ux.intel.com, tglx@...utronix.de, hpa@...ux.intel.com
Subject: [tip:x86/uaccess] x86: Add 1/2/4/
 8 byte optimization to 64bit __copy_{from,to}_user_inatomic

Commit-ID:  ff47ab4ff3cddfa7bc1b25b990e24abe2ae474ff
Gitweb:     http://git.kernel.org/tip/ff47ab4ff3cddfa7bc1b25b990e24abe2ae474ff
Author:     Andi Kleen <ak@...ux.intel.com>
AuthorDate: Fri, 16 Aug 2013 14:17:19 -0700
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Tue, 10 Sep 2013 15:27:43 -0700

x86: Add 1/2/4/8 byte optimization to 64bit __copy_{from,to}_user_inatomic

The 64bit __copy_{from,to}_user_inatomic always called
copy_from_user_generic, but skipped the special optimizations for 1/2/4/8
byte accesses.

This especially hurts the futex call, which accesses the 4 byte futex
user value with a complicated fast string operation in a function call,
instead of a single movl.

Use __copy_{from,to}_user for _inatomic instead to get the same
optimizations. The only problem was the might_fault() in those functions.
So move that to new wrapper and call __copy_{f,t}_user_nocheck()
from *_inatomic directly.

32bit already did this correctly by duplicating the code.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Link: http://lkml.kernel.org/r/1376687844-19857-2-git-send-email-andi@firstfloor.org
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/include/asm/uaccess_64.h | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index 4f7923d..64476bb 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -77,11 +77,10 @@ int copy_to_user(void __user *dst, const void *src, unsigned size)
 }
 
 static __always_inline __must_check
-int __copy_from_user(void *dst, const void __user *src, unsigned size)
+int __copy_from_user_nocheck(void *dst, const void __user *src, unsigned size)
 {
 	int ret = 0;
 
-	might_fault();
 	if (!__builtin_constant_p(size))
 		return copy_user_generic(dst, (__force void *)src, size);
 	switch (size) {
@@ -121,11 +120,17 @@ int __copy_from_user(void *dst, const void __user *src, unsigned size)
 }
 
 static __always_inline __must_check
-int __copy_to_user(void __user *dst, const void *src, unsigned size)
+int __copy_from_user(void *dst, const void __user *src, unsigned size)
+{
+	might_fault();
+	return __copy_from_user_nocheck(dst, src, size);
+}
+
+static __always_inline __must_check
+int __copy_to_user_nocheck(void __user *dst, const void *src, unsigned size)
 {
 	int ret = 0;
 
-	might_fault();
 	if (!__builtin_constant_p(size))
 		return copy_user_generic((__force void *)dst, src, size);
 	switch (size) {
@@ -165,6 +170,13 @@ int __copy_to_user(void __user *dst, const void *src, unsigned size)
 }
 
 static __always_inline __must_check
+int __copy_to_user(void __user *dst, const void *src, unsigned size)
+{
+	might_fault();
+	return __copy_to_user_nocheck(dst, src, size);
+}
+
+static __always_inline __must_check
 int __copy_in_user(void __user *dst, const void __user *src, unsigned size)
 {
 	int ret = 0;
@@ -220,13 +232,13 @@ int __copy_in_user(void __user *dst, const void __user *src, unsigned size)
 static __must_check __always_inline int
 __copy_from_user_inatomic(void *dst, const void __user *src, unsigned size)
 {
-	return copy_user_generic(dst, (__force const void *)src, size);
+	return __copy_from_user_nocheck(dst, (__force const void *)src, size);
 }
 
 static __must_check __always_inline int
 __copy_to_user_inatomic(void __user *dst, const void *src, unsigned size)
 {
-	return copy_user_generic((__force void *)dst, src, size);
+	return __copy_to_user_nocheck((__force void *)dst, src, size);
 }
 
 extern long __copy_user_nocache(void *dst, const void __user *src,
--
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