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

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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.
> >
> 
> I managed to reproduce a kasan backtrace on the same test.
> So it's not just the CI machine.

For the record, CI also seems much happier with the wait for OACONTROL
before unpinning, so no need to panic!
-Chris



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