linux-kernel - wby mapping beyond end by "MAPPING_BEYOND

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Message-ID: <CABymN7bseS2jNxxb1ZiaO9Yu3qaPmY_HrR6O8sLuRMb5qnd74Q@mail.gmail.com>
Date:	Fri, 21 Dec 2012 14:52:06 +0800
From:	Wang Baisheng <baisheng.wang.cn@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: wby mapping beyond end by "MAPPING_BEYOND_END" ?

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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