[Bugme-new] [Bug 12464] New: PAT: X.Org crash and console corruption caused by PAT?

[bugme-daemon at bugzilla.kernel.org]

http://bugzilla.kernel.org/show_bug.cgi?id=12464

           Summary: PAT: X.Org crash and console corruption caused by PAT?
           Product: Memory Management
           Version: 2.5
     KernelVersion: 2.6.28
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
        AssignedTo: akpm at osdl.org
        ReportedBy: elendil at planet.nl
                CC: venkatesh.pallipadi at intel.com, suresh.b.siddha at intel.com


I've been seeing regular crashes of X.Org with 2.6.28, each with the same
symptoms. However, I've not yet been able to reproduce the issue on demand.

The symptoms are:
- X.Org crashes after starting VirtualBox (both versions 2.0.1 and 2.1.0)
- after that, the display on VT1 is corrupted when I switch to that

One thing that I have discovered is that when the problem occurs, I have a
duplicate entry in /sys/kernel/debug/x86/pat_memtype_list which is not there
when the system is OK. The diff is (full list attached):

@@ -1,5 +1,6 @@
 PAT memtype list:
 uncached-minus @ 0x7e7b0000-0x7e7b1000
+uncached-minus @ 0x7e7b0000-0x7e7b1000
 uncached-minus @ 0x7e7c4000-0x7e7c5000
 uncached-minus @ 0x7e7c5000-0x7e7c8000
 uncached-minus @ 0x7e7c5000-0x7e7c7000

I'm not sure if the duplicate line gets added before or after the X.Org crash.

I am using the VESA framebuffer on VT1 (vga=791). The corruption is that after
a console switch most of the display is black, at the bottom there is an area
of grey horizontal stripes, and at the top there is a small bar where the text
of the console looks to be displayed, but in an extremely small font
(unreadable, but you can just recognize console messages "scrolling" in that
area).
Switching back from VT1 to X.Org works correctly, and if I log in to X.Org 
again and retry VirtualBox it works correctly. A reboot is needed to get VT1
displayed correctly again.

The problem occurs on a notebook which I use both undocked and docked. When
docked, an external monitor is connected and I use xrandr for dual-display
(Xinerama, with external monitor as display 1 and notebook monitor as display
2). I switch the notebook display on and off as needed when docked.

Most of the time starting VirtualBox does not cause any problem and console
switching to VT1 is OK too. My impression is that the error only occurs after I
have undocked or docked the notebook. I have a script running that checks for
dock/undock events and then calls xrandr to automatically enable/disable the
external display.

System is HP 2510p notebook running 2.6.28 x86_64, Debian Lenny, KDE desktop.

I will now try running 2.6.28 with 'nopat' and see if I then still see the
issue; I will also try 2.6.29 when I can.

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