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

[Paneer Selvam, Arunpravin]

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.

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
>>>>