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

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Date:	Tue, 20 May 2008 08:31:31 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Hugh Dickins <hugh@...itas.com>, Theodore Tso <tytso@....edu>,
	Gabriel C <nix.or.die@...glemail.com>,
	Keith Packard <keithp@...thp.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	bugme-daemon@...zilla.kernel.org, airlied@...ux.ie,
	"Barnes, Jesse" <jesse.barnes@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [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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