Bug 100971 - Doing a CLFLUSH on GTT-mapped memory causes a system reboot
Summary: Doing a CLFLUSH on GTT-mapped memory causes a system reboot
Alias: None
Product: DRI
Classification: Unclassified
Component: DRM/Intel (show other bugs)
Version: XOrg git
Hardware: Other All
: medium critical
Assignee: Intel GFX Bugs mailing list
QA Contact: Intel GFX Bugs mailing list
Depends on:
Reported: 2017-05-08 15:08 UTC by Jason Ekstrand
Modified: 2017-07-27 16:41 UTC (History)
2 users (show)

See Also:
i915 platform:
i915 features:


Description Jason Ekstrand 2017-05-08 15:08:25 UTC
Hardware: BXT laptop

Kernel: 4.11.something.  I think it's one of Rob or Lionel's OA branches.  I'll let Ken provide a few more details.

I was trying to figure out how to force the CPU to flush it's write-combine buffers (the kernel wasn't flushing them when EXEC_OBJECT_ASYNC is set).  This prompted me to start experimenting with different operations on GTT-mapped BOs and see if I could do something to uncached memory that would trigger a WC flush in the CPU from userspace.  I never succeeded, but I did manage to get some interesting behavior.

The moment I added a CLFLUSH (which is an unprivileged command) to flush a cache line that's mapped from the GTT, I immediately got system reboots.  It seems 100% reproducable.  I've pushed a Vulkan driver branch here which reproduces it:


However, I think you could probably reproduce with an utterly trivial IGT test if you don't want the full Vulkan driver.  I'm fairly sure the culprit is the CLFLUSH of GTT-mapped memory.
Comment 1 Chris Wilson 2017-05-08 20:38:52 UTC
This doesn't appear to be the appropriate forum for this; we need to raise this internally (assuming it isn't already known).

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