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From: Frans Pop <elendil@planet.nl>
To: linux-kernel@vger.kernel.org
Subject: [git head] Should X86_PAT really default to yes?
Date: Fri, 2 May 2008 21:22:03 +0200
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       Ingo Molnar <mingo@elte.hu>
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With X86_PAT enabled, when X is started I get about 40 lines (with varying 
addresses) like:
kernel: Xorg:3358 /dev/mem expected mapping type write-back for 
807bf000-81000000, got uncached-minus

And when X exits I get a bunch of lines like:
kernel: Xorg:3349 freeing invalid memtype 80020000-8002a000

I also noticed artifacts (a band of about 2 cm high across the screen) after 
X goes to black but before the switch to VT1.

When I unset X86_PAT all this disappeared.

Apparently this has been seen before:
http://lkml.org/lkml/2008/5/2/139

The author of that mail also points to:
http://marc.info/?l=linux-kernel&m=120612742217604&w=2

Is this a bug in PAT or not. If it is, should PAT really be recommended to 
be enabled by default?

System: Intel desktop with D945GCZ mainboard
        Intel(R) Pentium(R) D CPU 3.20GHz
        x86_64 kernel; Debian unstable
Video:  00:02.0 VGA compatible controller [0300]:
        Intel Corporation 82945G/GZ Integrated Graphics Controller
        [8086:2772] (rev 02)

Cheers,
FJP