• Christophe Leroy's avatar
    powerpc/8xx: reintroduce 16K pages with HW assistance · 55c8fc3f
    Christophe Leroy authored
    Using this HW assistance implies some constraints on the
    page table structure:
    - Regardless of the main page size used (4k or 16k), the
    level 1 table (PGD) contains 1024 entries and each PGD entry covers
    a 4Mbytes area which is managed by a level 2 table (PTE) containing
    also 1024 entries each describing a 4k page.
    - 16k pages require 4 identifical entries in the L2 table
    - 512k pages PTE have to be spread every 128 bytes in the L2 table
    - 8M pages PTE are at the address pointed by the L1 entry and each
    8M page require 2 identical entries in the PGD.
    
    In order to use hardware assistance with 16K pages, this patch does
    the following modifications:
    - Make PGD size independent of the main page size
    - In 16k pages mode, redefine pte_t as a struct with 4 elements,
    and populate those 4 elements in __set_pte_at() and pte_update()
    - Adapt the size of the hugepage tables.
    - Define a PTE_FRAGMENT_NB so that a 16k page contains 4 page tables.
    Signed-off-by: default avatarChristophe Leroy <christophe.leroy@c-s.fr>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    55c8fc3f
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