Re: [Intel-gfx] [PATCH v3 0/2] Don't use stolen memory or BAR mappings for ring buffers

[John Harrison <john.c.harrison@intel.com>]

On 2/17/2023 00:39, Hogander, Jouni wrote:
> On Wed, 2023-02-15 at 17:10 -0800, John.C.Harrison@Intel.com wrote:
>> From: John Harrison <John.C.Harrison@Intel.com>
>>
>> Instruction from hardware arch is that stolen memory and BAR mappings
>> are unsafe for use as ring buffers. There can be issues with cache
>> aliasing due to the CPU access going to memory via the BAR. So, don't
>> do it.
> Tested these patches for GPU Hang I was debugging. Seem to fix that one
> as well:
>
> Tested-by: Jouni Högander <jouni.hogander@intel.com>
Sweet! Out of interest, which platform was that? And how reproducible 
was it? It would be interesting to know if an IGT was actually regularly 
showing the issue and we had just been ignoring it!

John.

>
>> v2: Dont use BAR mappings either.
>> Make conditional on LLC so as not to change platforms that don't need
>> to change (Daniele).
>> Add 'Fixes' tags (Tvrtko).
>> v3: Fix dumb typo.
>>
>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
>>
>>
>> John Harrison (2):
>>    drm/i915: Don't use stolen memory for ring buffers with LLC
>>    drm/i915: Don't use BAR mappings for ring buffers with LLC
>>
>>   drivers/gpu/drm/i915/gt/intel_ring.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>