Comment 11 for bug 975689

It looks like this is a kernel issue rather than a xserver issue, as kernel commit 3a69ddd6f872180b6f61fda87152b37202118fbc fixes the problem for me:

commit 3a69ddd6f872180b6f61fda87152b37202118fbc
Author: Kenneth Graunke <email address hidden>
Date: Fri Apr 27 12:44:41 2012 -0700

    drm/i915: Set the Stencil Cache eviction policy to non-LRA mode.

    Clearing bit 5 of CACHE_MODE_0 is necessary to prevent GPU hangs in
    OpenGL programs such as Google MapsGL, Google Earth, and gzdoom when
    using separate stencil buffers. Without it, the GPU tries to use the
    LRA eviction policy, which isn't supported. This was supposed to be off
    by default, but seems to be on for many machines.

    This cannot be done in gen6_init_clock_gating with most of the other
    workaround bits; the render ring needs to exist. Otherwise, the
    register write gets dropped on the floor (one printk will show it
    changed, but a second printk immediately following shows the value
    reverts to the old one).

    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=47535
    Cc: <email address hidden>
    Cc: Rob Castle <email address hidden>
    Cc: Eric Appleman <email address hidden>
    Cc: <email address hidden>
    Cc: Keith Packard <email address hidden>
    Signed-off-by: Kenneth Graunke <email address hidden>
    Reviewed-by: Daniel Vetter <email address hidden>
    Acked-by: Daniel Vetter <email address hidden>
    Signed-off-by: Dave Airlie <email address hidden>