Re: [PATCH] drm/i915/oa: Disable OA on Haswell

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Quoting Lionel Landwerlin (2018-05-11 16:58:27)
> On 11/05/18 16:51, Chris Wilson wrote:
> > Quoting Lionel Landwerlin (2018-05-11 16:43:02)
> >> On 11/05/18 15:18, Chris Wilson wrote:
> >>> Quoting Lionel Landwerlin (2018-05-11 15:14:13)
> >>>> My understanding of the virtual memory addressing from the GPU is limited...
> >>>> But how can the GPU poke at the kernel's allocated data?
> >>>> I thought we mapped into the GPU's address space only what is allocated
> >>>> through gem.
> >>> Correct. The HW should only be accessing the pages through the GTT and
> >>> the GTT should only contain known pages (or a pointer to the scratch
> >>> page). There is maybe a hole where we are freeing the memory before
> >>> the HW has finished using it (still writing through stale TLB and
> >>> whatnot even though the system has reallocated the pages), but other
> >>> than that quite, quite scary. Hence this awooga.
> >>> -Chris
> >>>
> >> I managed to reproduce a kasan backtrace on the same test.
> >> So it's not just the CI machine.
> >>
> >> But I can't even startup a gdm on that machine with drm-tip. So maybe
> >> there is some much more broken...
> > Don't leave us in suspense...
> 
> Your first patch (check that OA is actually disabled) seems to get rid 
> of the issue on my machine.
> Thanks a lot a for finding that!

Care to add a t-b and we'll close the bug?
-Chris



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