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    SubjectRe: [Bug 10732] REGRESSION: 2.6.26-rc2-git4: X server failed start onX61s laptop

    On Mon, 19 May 2008, Hugh Dickins wrote:
    > This comes from an assumption in 1c12c4cf9411eb130b245fa8d0fbbaf989477c7b
    > mprotect: prevent alteration of the PAT bits, that PTE_MASK is what it's
    > supposed to be: whereas it's been wrong forever with PAE, staying 32-bit
    > where 64-bit is needed.

    Can we *please* just fix PTE_MASK?

    And can we agree to never EVER use that PAGE_MASK thing (which was only
    ever meant to work on *addresses*) for any pte operations (including the
    definition of PTE_MASK)? Because PAGE_MASK is very much the word-size, and
    in 32-bit PAE, the page table entry is bigger.

    IOE, PTE_MASK should be a "pteval_t". And it should have absolutely
    *nothing* to do with PAGE_MASK. EVER.

    IOW, maybe something like this?

    And no, I haven't tested this at all. But it should make PTE_MASK have
    (a) the right type ("pteval_t", not "long" - the latter is pure and utter
    (b) the right value (proper mask, not a sign-extended long - again, the
    latter is pure and utter crap)

    but for all I know there might be some broken code that depends on the
    current incorrect and totally broken #defines, so this needs testing and
    thinking about.

    It also causes these warnings on 32-bit PAE:

    AS arch/x86/kernel/head_32.o
    arch/x86/kernel/head_32.S: Assembler messages:
    arch/x86/kernel/head_32.S:225: Warning: left operand is a bignum; integer 0 assumed
    arch/x86/kernel/head_32.S:609: Warning: left operand is a bignum; integer 0 assumed

    and I do not see why (the end result seems to be identical).

    Ingo, comments?

    Oh, and those #define's should be moved from <asm/page.h> to
    <asm/pgtable.h>, I think. They have nothing to do with pages (despite the
    name of "physical_page_mask", and really are meaningful only in the
    context of some kind of page table entry.


    include/asm-x86/page.h | 5 +++--
    1 files changed, 3 insertions(+), 2 deletions(-)

    diff --git a/include/asm-x86/page.h b/include/asm-x86/page.h
    index b381f4a..34b4845 100644
    --- a/include/asm-x86/page.h
    +++ b/include/asm-x86/page.h
    @@ -10,8 +10,8 @@

    #ifdef __KERNEL__

    -#define PTE_MASK (_AT(long, PHYSICAL_PAGE_MASK))
    +#define PTE_MASK (_AT(pteval_t, PHYSICAL_PAGE_MASK))

    #define PMD_PAGE_SIZE (_AC(1, UL) << PMD_SHIFT)
    #define PMD_PAGE_MASK (~(PMD_PAGE_SIZE-1))
    @@ -24,6 +24,7 @@
    /* to align the pointer to the (next) page boundary */
    #define PAGE_ALIGN(addr) (((addr)+PAGE_SIZE-1)&PAGE_MASK)

    +#define __PHYSICAL_LOW_BITS _AT(phys_addr_t, (PAGE_SIZE-1))
    #define __PHYSICAL_MASK _AT(phys_addr_t, (_AC(1,ULL) << __PHYSICAL_MASK_SHIFT) - 1)
    #define __VIRTUAL_MASK ((_AC(1,UL) << __VIRTUAL_MASK_SHIFT) - 1)

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      Last update: 2008-05-20 01:13    [W:0.024 / U:2.420 seconds]
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