[PATCH v2] drm: add a check to verify the size alignment

[Arunpravin Paneer Selvam]

On 23/03/22 1:15 pm, Christian König wrote:
> Am 23.03.22 um 08:34 schrieb Arunpravin Paneer Selvam:
>> Add a simple check to reject any size not aligned to the
>> min_page_size.
>>
>> handle instances when size is not aligned with the min_page_size.
>> Unigine Heaven has allocation requests for example required pages
>> are 257 and alignment request is 256. To allocate the left over 1
>> page, continues the iteration to find the order value which is 0
>> and when it compares with min_order = 8, triggers the BUG_ON(order
>> < min_order). To avoid this problem, we added a simple check to
>> return -EINVAL if size is not aligned to the min_page_size.
>>
>> v2: Added more details to the commit description
>>
>> Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
>> Suggested-by: Matthew Auld <matthew.auld at intel.com>
>> ---
>>   drivers/gpu/drm/drm_buddy.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>> index 72f52f293249..b503c88786b0 100644
>> --- a/drivers/gpu/drm/drm_buddy.c
>> +++ b/drivers/gpu/drm/drm_buddy.c
>> @@ -661,6 +661,9 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>>   	if (range_overflows(start, size, mm->size))
>>   		return -EINVAL;
>>   
>> +	if (WARN_ON(!IS_ALIGNED(size, min_page_size)))
>> +		return -EINVAL;
>> +
> 
> I'm not that happy with the handling here.
> 
> See a minimum page size larger than the requested size is perfectly 
> valid, it just means that the remaining pages needs to be trimmed.
> 
> In other words when the request is to allocate 1 page with an alignment 
> of 256 we just need to give the remaining 255 pages back to the allocator.

In one of the previous mail Matthew explained that i915 expects to
return -EINVAL error code if size is not aligned to min_page_size.

can we just modify in amdgpu code where we round_up the size to the
min_page_size value and keep this error handling in drm_buddy.c?
> 
> Regards,
> Christian.
> 
>>   	/* Actual range allocation */
>>   	if (start + size == end)
>>   		return __drm_buddy_alloc_range(mm, start, size, blocks);
>>
>> base-commit: 056d47eaf6ea753fa2e21da31f9cbd8b721bbb7b
>