why mapping beyond end "MAPPING_BEYOND_END"?

Wang Baisheng <baisheng.wang.cn@xxxxxxxxx> · Fri, 21 Dec 2012 14:50:57 +0800

Hi All,

For x86, in arch/x86/kernel/head_32.S, for Initializing page tables,
why mapping beyond end by "MAPPING_BEYOND_END":

    /*
     * End condition: we must map up to the end + MAPPING_BEYOND_END.
     */
    movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
    cmpl %ebp,%eax
    jb 10b

According vmlinux.lds.S, the paging table is between __brk_base and
_end. So why map MAPPING_BEYOND_END after _end ?

Regards,
Jacky
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