[PATCH] drm/amdgpu: refuse to reserve io mem for split VRAM buffers

[Christian König]

Am 17.02.2017 um 00:21 schrieb Nicolai Hähnle:
> On 17.02.2017 00:02, Alex Deucher wrote:
>> On Thu, Feb 16, 2017 at 5:55 PM, Nicolai Hähnle <nhaehnle at gmail.com> 
>> wrote:
>>> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>>>
>>> When the fast blit path fails while attempting to move a buffer from 
>>> RAM
>>> to VRAM, we fall back to a CPU-based memcpy that cannot handle split 
>>> VRAM
>>> buffers. Instead of crashing, simply fail the buffer move.
>>>
>>> Ideally, we would teach TTM about split buffers so that the fallback 
>>> still
>>> works in this case, but that is quite involved. So for now, apply the
>>> simplest possible fix.
>>>
>>> Fixes: 40361bb1704b ("drm/amdgpu: add VRAM manager v2")
>>> Signed-off-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
>>
>> Possibly fixes this bug report?
>> https://bugzilla.kernel.org/show_bug.cgi?id=194579
>
> It's related, but I think that report is a false positive. It does 
> point at code that is not too pretty, though. I've commented on that 
> bug report as well.
>
> In any case, that overflow should indeed happen whenever the bug 
> addressed by this patch happens, but (a) this patch doesn't change 
> that, and (b) I'm pretty sure that the overflow reported by PaX is 
> benign.

Yes, agree. The bug report is indeed a false positive.

Nicolai what do you think about removing the offset from the BO 
structure and only calculate it on demand?

>
> We may still have other bugs with split BOs, though.

Yeah, agree as well. I was also considering disabling that feature by 
default for the moment if it helps with your corruption bug.

Regards,
Christian.

>
> Cheers,
> Nicolai
>
>>
>> Alex
>>
>>> -- 
>>> I ran into this bug during testing. Unfortunately it does not fix the
>>> memory corruption bug that I mentioned elsewhere... oh well.
>>> ---
>>>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>> index 8d6a68f..f8b578d 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>> @@ -529,6 +529,9 @@ static int amdgpu_ttm_io_mem_reserve(struct 
>>> ttm_bo_device *bdev, struct ttm_mem_
>>>         case TTM_PL_TT:
>>>                 break;
>>>         case TTM_PL_VRAM:
>>> +               if (mem->start == AMDGPU_BO_INVALID_OFFSET)
>>> +                       return -EINVAL;
>>> +
>>>                 mem->bus.offset = mem->start << PAGE_SHIFT;
>>>                 /* check if it's visible */
>>>                 if ((mem->bus.offset + mem->bus.size) > 
>>> adev->mc.visible_vram_size)
>>> -- 
>>> 2.9.3
>>>
>>> _______________________________________________
>>> amd-gfx mailing list
>>> amd-gfx at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
>
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