Note: this patch depends on "Correct improper large page preservation" patch
    
    This patch expands functionality of CONFIG_DEBUG_RODATA to set main
    (static) kernel data area as NX.
    The following steps are taken to achieve this:
    1. Linker script is adjusted so .text always starts and ends on a page bound
    2. Linker script is adjusted so .rodata always start and
    end on a page boundary
    3. NX is set for all pages from _etext through _end in mark_rodata_ro.
    4. free_init_pages() sets released memory NX in arch/x86/mm/init.c
    5. bios rom is set to x when pcibios is used.
    
    The results of patch application may be observed in the diff of kernel page
    table dumps.
    pcibios :
    --- data_nx_pt_before.txt       2009-10-13 07:48:59.000000000 -0400
    +++ data_nx_pt_after.txt        2009-10-13 07:26:46.000000000 -0400
    @@ -2,8 +2,9 @@
     0x00000000-0xc0000000           3G                           pmd
     ---[ Kernel Mapping ]---
    -0xc0000000-0xc0100000           1M     RW             GLB x  pte
    +0xc0000000-0xc00a0000         640K     RW             GLB NX pte
    +0xc00a0000-0xc0100000         384K     RW             GLB x  pte
    -0xc0100000-0xc03d7000        2908K     ro             GLB x  pte
    +0xc0100000-0xc0318000        2144K     ro             GLB x  pte
    +0xc0318000-0xc03d7000         764K     ro             GLB NX pte
    -0xc03d7000-0xc0600000        2212K     RW             GLB x  pte
    +0xc03d7000-0xc0600000        2212K     RW             GLB NX pte
     0xc0600000-0xf7a00000         884M     RW         PSE GLB NX pmd
     0xf7a00000-0xf7bfe000        2040K     RW             GLB NX pte
     0xf7bfe000-0xf7c00000           8K                           pte
    
    no pcibios :
    --- data_nx_pt_before.txt       2009-10-13 07:48:59.000000000 -0400
    +++ data_nx_pt_after.txt        2009-10-13 07:26:46.000000000 -0400
    @@ -2,8 +2,9 @@
     0x00000000-0xc0000000           3G                           pmd
     ---[ Kernel Mapping ]---
    -0xc0000000-0xc0100000           1M     RW             GLB x  pte
    +0xc0000000-0xc0100000           1M     RW             GLB NX pte
    -0xc0100000-0xc03d7000        2908K     ro             GLB x  pte
    +0xc0100000-0xc0318000        2144K     ro             GLB x  pte
    +0xc0318000-0xc03d7000         764K     ro             GLB NX pte
    -0xc03d7000-0xc0600000        2212K     RW             GLB x  pte
    +0xc03d7000-0xc0600000        2212K     RW             GLB NX pte
     0xc0600000-0xf7a00000         884M     RW         PSE GLB NX pmd
     0xf7a00000-0xf7bfe000        2040K     RW             GLB NX pte
     0xf7bfe000-0xf7c00000           8K                           pte
    
    The patch have been developed for Linux 2.6.34-rc2 x86 by Siarhei Liakh
    <sliakh.lkml@gmail.com> and Xuxian Jiang <jiang@cs.ncsu.edu>.
    
    V1:  initial patch for 2.6.30
    V2:  patch for 2.6.31-rc7
    V3:  moved all code into arch/x86, adjusted credits
    V4:  fixed ifdef, removed credits from CREDITS
    V5:  fixed an address calculation bug in mark_nxdata_nx()
    V6:  added acked-by and PT dump diff to commit log
    V7:  minor adjustments for -tip
    V8:  rework with the merge of "Set first MB as RW+NX"
    
    Signed-off-by: Siarhei Liakh <sliakh.lkml@gmail.com>
    Signed-off-by: Xuxian Jiang <jiang@cs.ncsu.edu>
    Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>