[RFC PATCH 1/2] drm/amdgpu: amdgpu_vram_mgr_new(): Clamp lpfn to total vram

[Paneer Selvam, Arunpravin]

On 5/12/2025 12:39 PM, Christian König wrote:
>
> On 5/11/25 22:37, Paneer Selvam, Arunpravin wrote:
>>
>> On 5/12/2025 2:03 AM, Paneer Selvam, Arunpravin wrote:
>>>
>>> On 5/3/2025 5:53 PM, Paneer Selvam, Arunpravin wrote:
>>>>
>>>> On 5/2/2025 9:02 PM, John Olender wrote:
>>>>> On 4/30/25 5:44 PM, Paneer Selvam, Arunpravin wrote:
>>>>>> On 5/1/2025 2:50 AM, Alex Deucher wrote:
>>>>>>> + Christian
>>>>>>>
>>>>>>> On Tue, Apr 29, 2025 at 7:24 AM John Olender <john.olender at gmail.com>
>>>>>>> wrote:
>>>>>>>> The drm_mm allocator tolerated being passed end > mm->size, but the
>>>>>>>> drm_buddy allocator does not.
>>>>>>>>
>>>>>>>> Restore the pre-buddy-allocator behavior of allowing such placements.
>>>>>>>>
>>>>>>>> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3448
>>>>>>>> Signed-off-by: John Olender <john.olender at gmail.com>
>>>>>>> This looks correct to me.
>>>>>>> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
>>>>>> I was thinking that we should return an error when lpfn > man->size.
>>>>>>
>>>>>> Regards,
>>>>>> Arun.
>>>>> This patch restores the previous behavior in the spirit of "Do not crash
>>>>> the kernel".  The existing uvd placements are pretty clear in their
>>>>> intent and were accepted until the switch to drm_buddy.  I think it's
>>>>> fair to consider their style as expected.
>>>>>
>>>>> With that in mind, I'm not sure amdgpu_vram_mgr is the place this change
>>>>> really belongs.  That is, I think it's worth asking:
>>>>>
>>>>> 1) Why does drm_mm accept end > mm->size without complaint?
>>>>> 2) Why doesn't drm_buddy do the same?
>>>> I remember that during the development of DRM buddy , we had a discussion with Intel folks and decided to
>>>> return an error in DRM buddy when end > mm->size. This was done to ensure that, at the driver level,  lpfn
>>>> has the correct value.
>>>>
>>>> I will modify this at drm_buddy to match with drm_mm and send the patch.
>>> After giving it some thought, I think it is more effective to implement this tolerance at the VRAM manager level
>>> and allow the DRM buddy manager to perform a strict validation, as this is necessary for other graphics drivers
>>> (e.g., i915).
>> Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
> Ok in that case please pick this patch up and make sure that it land in amd-staging-drm-next Arun.
>
> Alex most likely won't follow the discussion till the end.
Sure Christian, I will merge this patch into amd-staging-drm-next.

Thanks,
Arun.
>
> Thanks,
> Christian.
>
>>> Regards,
>>> Arun.
>>>> Regards,
>>>> Arun.
>>>>> Thanks,
>>>>> John
>>>>>
>>>>>>>> ---
>>>>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 2 +-
>>>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/
>>>>>>>> gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
>>>>>>>> index 2d7f82e98df9..abdc52b0895a 100644
>>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
>>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
>>>>>>>> @@ -463,7 +463,7 @@ static int amdgpu_vram_mgr_new(struct
>>>>>>>> ttm_resource_manager *man,
>>>>>>>>            int r;
>>>>>>>>
>>>>>>>>            lpfn = (u64)place->lpfn << PAGE_SHIFT;
>>>>>>>> -       if (!lpfn)
>>>>>>>> +       if (!lpfn || lpfn > man->size)
>>>>>>>>                    lpfn = man->size;
>>>>>>>>
>>>>>>>>            fpfn = (u64)place->fpfn << PAGE_SHIFT;
>>>>>>>> -- 
>>>>>>>> 2.47.2
>>>>>>>>