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 00:04:23 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Hugh Dickins <hugh@...itas.com>
CC:	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>,
	Linus Torvalds <torvalds@...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:
> On Sat, 17 May 2008, Theodore Tso wrote:
>   
>> On Sat, May 17, 2008 at 08:32:38PM +0200, Gabriel C wrote:
>>     
>>>> Which repository is commit 1c12c4cf in?
>>>>         
>>> It is in linus-git tree , http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1c12c4cf9411eb130b245fa8d0fbbaf989477c7b
>>>       
>> ...post 2.6.26-rc2-git3.  For Linux kernels 2.6.26-rc2-git4 and
>> newer, you need to revert this commit or the X Server shipped with
>> Ubuntu Gutsy will die horribly when run on an X61s laptop with the
>> Intel 965GM video chipset.
>>
>> So the question is what's the right fix to keep the kernel compatible
>> with the X server, besides just reverting the commit entirely?
>>     
>
> [PATCH] x86: fix mprotect's NX handling on PAE
>
> 2.6.26-rc3 with CONFIG_X86_PAE may leave the NX bit set when PROT_EXEC
> is intending to clear it, causing irqbalance and others to segfault,
> and X startup to fail.
>
> 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.
>
> Jeremy Fitzhardinge already has patches to fix that in Ingo's tree;
> but if they're not considered 2.6.26 material, or people want a quick
> two-liner to get working, here's a shorter hack to fix up pte_modify.
>   

 From what I can tell, my patches haven't caused any regressions, and so 
if they fix a real bug we could consider them for .26.

    J
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