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Subject: Re: [PATCH] drm/i915/oa: Disable OA on Haswell
To: Chris Wilson <chris@chris-wilson.co.uk>,
        intel-gfx@lists.freedesktop.org
Cc: Matthew Auld <matthew.auld@intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
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From: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Message-ID: <b8ca952e-3713-4d38-10a4-774f515cc2fd@intel.com>
Date: Fri, 11 May 2018 15:37:43 +0100
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On 11/05/18 15:34, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2018-05-11 15:28:24)
>> 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.
>>>
>> Oh right...
>>
>> So this patch is a backup if you previous one won't fix the issue we see
>> on CI?
> Yes. Try to fix, it we can't, we disable until we can. It may also be
> purely coincidental that we've seen this bug a few times around the same
> test only on this machine... ;)
> -Chris
>
Trying on a laptop.