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SubjectRe: [Bug 10732] REGRESSION: 2.6.26-rc2-git4: X server failed start onX61s laptop
Linus Torvalds wrote:
> 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?
>

That's pretty close to the core of my patches (just reposted), which
have been cooking in x86.git for a week or so.

One thing I'd take from your patch is something like your
__PHYSICAL_LOW_BITS definition, since its a bit clearer than what I
did. (I haven't updated my patch before posting just because I wanted
to post exactly as tested.)

> 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
> crap)
> (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.
>
> Linus
>
> ---
> 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 PHYSICAL_PAGE_MASK (PAGE_MASK & __PHYSICAL_MASK)
> -#define PTE_MASK (_AT(long, PHYSICAL_PAGE_MASK))
> +#define PHYSICAL_PAGE_MASK (__PHYSICAL_MASK & ~__PHYSICAL_LOW_BITS)
> +#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)
>
>

J


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