[Bug 110774] Xorg segfault on cpu which does not support PAT

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110774

            Bug ID: 110774
           Summary: Xorg segfault on cpu which does not support PAT
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: ssheribe at redhat.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 144351
  --> https://bugs.freedesktop.org/attachment.cgi?id=144351&action=edit
gdb bt

My setup is as follow:

OS: fedora 30 5.0.11-300
cpu: QEMU Virtual CPU 2.5+ (without PAT - qemu's default)
gpu: assigned vGPU using GVTg 
mesa-dri-drivers: 19.0.3-1
xorg-x11-server-Xorg: 1.20.4-3

(This is a vm running on top of fedora 30 host, same kernel with Intel
i7-6600u)

When i'm running inside xorg session and trying to open firefox, xorg crashes.
bisecting points to this patch:
54c823ec790427acbea31212a6ed30a17bd25ff0 (mesa)

It seems that in case cpu does not support PAT, mapping may fail (brw_bo_map_wc
fails without PAT and won't fallback since MAP_RAW is set) so that
intel_miptree_map_raw will use *dst when it's NULL, passing it to
linear_to_tiled which is trying to access *dst(=NULL).

Backtrace is attached.

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