[Bug 108326] [BXT] BUG / system hang when reading i915 debugfs entries with VT-d/IOMMU enabled

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108326

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit fb6f0b64e455b207a636346588e65bf9598d30eb (HEAD -> drm-intel-next-queued,
drm-intel/for-linux-next, drm-intel/drm-intel-next-queued)
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri Nov 2 16:12:12 2018 +0000

    drm/i915: Prevent machine hang from Broxton's vtd w/a and error capture

    Since capturing the error state requires fiddling around with the GGTT
    to read arbitrary buffers and is itself run under stop_machine(), it
    deadlocks the machine (effectively a hard hang) when run in conjunction
    with Broxton's VTd workaround to serialize GGTT access.

    v2: Store the ERR_PTR in first_error so that the error can be reported
    to the user via sysfs.
    v3: Mention the quirk in dmesg (using info as per usual)

    Fixes: 0ef34ad6222a ("drm/i915: Serialize GTT/Aperture accesses on BXT")
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Jon Bloomfield <jon.bloomfield at intel.com>
    Cc: John Harrison <john.C.Harrison at intel.com>
    Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
    Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
    Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20181102161232.17742-5-chris@chris-wilson.co.uk

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