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    SubjectRe: [KJ PATCH] Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in arch/i386/kernel/machine_kexec.c
    Eric W. Biederman wrote:
    > Shani Moideen <shani.moideen@wipro.com> writes:
    >
    >> Hi,
    >> Replacing memcpy(dest,src,PAGE_SIZE) with copy_page(dest,src) in
    >> arch/i386/kernel/machine_kexec.c.
    >
    > Please no.
    >
    > People get creative in copy_page (especially mmx_copy_page),
    > and this code path need something simple and stupid, that
    > will work every time, especially when things are messed up
    > elsewhere.
    >

    memcpy() is pretty creative, too. If you want something really dumb and
    robust, you should probably create an inline:

    /*
    * Eric sez: his code path need something simple and stupid, that
    * will work every time, especially when things are messed up
    * elsewhere.
    */
    static inline void braindead_copy_page(void *dst, void *src)
    {
    unsigned long ctr = PAGE_SIZE >> 2;

    asm volatile("cld; rep; movsl"
    : "+D" (dst), "+S" (src), "+c" (ctr)
    : : "memory");
    }

    (FWIW, the "cld" is supposed to be redundant, as DF=0 is supposed to be
    guaranteed by the ABI.)

    -hpa
    -
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