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SubjectRe: [PATCH] x86: Optimize tail handling for copy_user
Date
Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Mon, 28 Jul 2008, Vitaly Mayatskikh wrote:
>>
>> Reduce protection faults count in copy_user_handle_tail routine by
>> limiting clear length to the end of page as was suggested by Linus.
>
> No, you did it wrong.

Another try. Added direction and clear remainder flags to let
handle tail routine know how to optimize tail copying and clearing.
BYTES_LEFT_IN_PAGE macro returns PAGE_SIZE, not zero, when the address
is well aligned to page.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>

diff --git a/include/asm-x86/uaccess_64.h b/include/asm-x86/uaccess_64.h
index 5cfd295..e0ddedf 100644
--- a/include/asm-x86/uaccess_64.h
+++ b/include/asm-x86/uaccess_64.h
@@ -1,6 +1,16 @@
#ifndef ASM_X86__UACCESS_64_H
#define ASM_X86__UACCESS_64_H

+/* Flags for copy_user_handle_tail */
+#define CLEAR_REMAINDER 1
+#define DEST_IS_USERSPACE 2
+#define SOURCE_IS_USERSPACE 4
+
+#define BYTES_LEFT_IN_PAGE(ptr) \
+ (unsigned)((PAGE_MASK & ((long)(ptr) + PAGE_SIZE)) - (long)(ptr))
+
+#ifndef __ASSEMBLY__
+
/*
* User space memory access functions
*/
@@ -179,23 +189,26 @@ __copy_to_user_inatomic(void __user *dst, const void *src, unsigned size)
}

extern long __copy_user_nocache(void *dst, const void __user *src,
- unsigned size, int zerorest);
+ unsigned size, unsigned flags);

static inline int __copy_from_user_nocache(void *dst, const void __user *src,
unsigned size)
{
might_sleep();
- return __copy_user_nocache(dst, src, size, 1);
+ return __copy_user_nocache(dst, src, size, SOURCE_IS_USERSPACE
+ | CLEAR_REMAINDER);
}

static inline int __copy_from_user_inatomic_nocache(void *dst,
const void __user *src,
unsigned size)
{
- return __copy_user_nocache(dst, src, size, 0);
+ return __copy_user_nocache(dst, src, size, SOURCE_IS_USERSPACE);
}

unsigned long
-copy_user_handle_tail(char *to, char *from, unsigned len, unsigned zerorest);
+copy_user_handle_tail(char *dst, char *src, unsigned remainder, unsigned flags);
+
+#endif /* __ASSEMBLY__ */

#endif /* ASM_X86__UACCESS_64_H */
--
wbr, Vitaly


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