[Bug 99028] [KVM][GVT-d] [BDW & SKL ]Ubuntu 16.04 guest boot up with GPU Hang with drm-intel kernel

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99028

--- Comment #24 from XiongZhang <xiong.y.zhang at intel.com> ---
I did the git bisect again, and the target commit is:
commit c58b735fc762e891481e92af7124b85cb0a51fce
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Thu Aug 18 17:16:57 2016 +0100

    drm/i915: Allocate rings from stolen

    If we have stolen available, make use of it for ringbuffer allocation.
    Previously this was restricted to !llc platforms, as writing to stolen
    requires a GGTT mapping - but now that we have partial mappable support,
    the mappable aperture isn't quite so precious so we can use it more
    freely and ringbuffers are a good user for the otherwise wasted stolen.

    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>


After reverting this patch from drm-intel-nightly, I didn't see gpu hang during
boot process. So we could confirm this issue is caused by i915 access stolen
memory when i915 is as kvm guest where kvm doesn't supply ept and guest domain
iommu mapping for stolen memory.

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