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    Subject[PATCH UPDATED] x86: set PAE PHYSICAL_MASK_SHIFT to 44 bits.
    When a 64-bit x86 processor runs in 32-bit PAE mode, a pte can
    potentially have the same number of physical address bits as the
    64-bit host ("Enhanced Legacy PAE Paging"). This means, in theory,
    we could have up to 52 bits of physical address in a pte.

    The 32-bit kernel uses a 32-bit unsigned long to represent a pfn.
    This means that it can only represent physical addresses up to 32+12=44
    bits wide. Rather than widening pfns everywhere, just set 2^44 as the
    Linux x86_32-PAE architectural limit for physical address size.

    Signed-off-by: Jeremy Fitzhardinge <>
    Cc: Jan Beulich <>
    include/asm-x86/page_32.h | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/include/asm-x86/page_32.h
    +++ b/include/asm-x86/page_32.h
    @@ -22,7 +22,8 @@

    #ifdef CONFIG_X86_PAE
    -#define __PHYSICAL_MASK_SHIFT 36
    +/* 44=32+12, the limit we can fit into an unsigned long pfn */
    +#define __PHYSICAL_MASK_SHIFT 44
    #define __VIRTUAL_MASK_SHIFT 32
    #define PAGETABLE_LEVELS 3

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      Last update: 2008-06-06 11:25    [W:0.020 / U:89.224 seconds]
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