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    Subject[PATCH] ppc32: kernel mapping breakage
    Hi !

    Christoph Lameter's patch that change page allocators to use GFP_ZERO
    broke ppc32 in a subtle way. Our allocator is designed to work before
    mem_init_done, in which cases it uses a ppc specific early_get_page()
    which doesn't return zeroed pages. However, he removed the call to
    clear_page() unconditionally, thus causing the kernel initial page
    tables to have random data in them.

    They are initialized with set_pte, which means it's _mostly_ harmless,
    except that set_pte on ppc32 preserves the _PAGE_HASHPTE bit, thus we
    end up with random bits there, which can cause issues with further
    manipulation of the kernel page tables and will slow down all hash
    faults to them causing unnecessary searches.

    Please apply in 2.6.11 if still possible ...

    Signed-off-by: Benjamin Herrenschmidt <>

    Index: linux-work/arch/ppc/mm/pgtable.c
    --- linux-work.orig/arch/ppc/mm/pgtable.c 2005-01-24 17:09:23.000000000 +1100
    +++ linux-work/arch/ppc/mm/pgtable.c 2005-02-23 14:31:41.000000000 +1100
    @@ -107,8 +107,11 @@
    ptepage->mapping = (void *) mm;
    ptepage->index = address & PMD_MASK;
    - } else
    + } else {
    pte = (pte_t *)early_get_page();
    + if (pte)
    + clear_page(pte);
    + }
    return pte;

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      Last update: 2005-03-22 14:10    [W:0.021 / U:41.968 seconds]
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