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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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