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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [BXT] BUG / system hang when reading i915 debugfs entries with VT-d/IOMMU enabled"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108326">108326</a>
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<th>Summary</th>
<td>[BXT] BUG / system hang when reading i915 debugfs entries with VT-d/IOMMU enabled
</td>
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<th>Product</th>
<td>DRI
</td>
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<th>Version</th>
<td>DRI git
</td>
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<th>Hardware</th>
<td>Other
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>DRM/Intel
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<th>Assignee</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
</tr>
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<th>Reporter</th>
<td>eero.t.tamminen@intel.com
</td>
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<th>QA Contact</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
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<th>CC</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
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<th>i915 platform</th>
<td>BXT
</td>
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<th>i915 features</th>
<td>GPU hang
</td>
</tr></table>
<p>
<div>
<pre>Setup:
- BXT / APL HW (e.g. J3455, J4205, A3960)
- git version of drm-tip kernel
- VT-d enabled in BIOS (normally it's enabled by default)
- IOMMU not disabled on kernel command line (no "intel_iommu=igfx_off" option)
Use-case:
- cd /sys/kernel/debug/dri/0/
- head *
Expected outcome:
- entries shown, like happens when VT-d / IOMMU is disabled
Actual outcome:
- System hangs after following console output (and sometimes backtrace):
[ 49.565898] BUG: scheduling while atomic: migration/0/11/0x00000002
[ 49.572983] Preemption disabled at:
Notes:
* I haven't seen this on any other (GEN7-GEN9) HW, only on BXT/APL
* Most distros seems to mount debugfs as user readable, so this is a local DOS
(security) issue
* I don't think this is a regression as it has been there at least for a year
(when I filed an internal ticket about this, which was now closed with a
request to file this to FDO instead)</pre>
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