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

[Christian König]

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.

Regards,
Christian.

>   	/* Actual range allocation */
>   	if (start + size == end)
>   		return __drm_buddy_alloc_range(mm, start, size, blocks);
>
> base-commit: 056d47eaf6ea753fa2e21da31f9cbd8b721bbb7b