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

[Christian König]

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.

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
>>>>>>>
>>>
>>
>