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

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Message-ID: <48327E92.4060201@goop.org>
Date:	Tue, 20 May 2008 08:32:34 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

Hugh Dickins wrote:
>> 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.
>>     
>
> Yes, Jeremy makes it a pteval_t.  (My builds and Ingo's builds succeed,
> but I've not worked out how that goes down in assembly: there was an
> _AT macro in there before, which you've kept too - Jeremy?)
>   

I got rid of a bunch of _AT() uses because the constants aren't used in 
.S files anywhere.  Also, I couldn't see how to represent a 64-bit 
constant in assembler, so I wasn't sure of their correctness (the as 
manual is irritatingly vague on the matter).

> Yes, I'm highly resistant to taking untested patches here.  The two-liner
> I sent last night was about my fifth attempt to get it working, and I did
> start off from a small PTE_MASK correction which didn't work at all.  It
> looked rather like yours, I guess I missed the  __PHYSICAL_LOW_BITS part.
> Jeremy's goes a lot further, he'll know the gotchas better.
>   

__PHYSICAL_LOW_BITS is a bit more elegant than what I did there (the 
problem is getting a physaddr_t-width PAGE_MASK).  But the formulation 
in my patch certainly works.

    J
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