On Fri, 13 Mar 2026 07:20:28 -0600, Jim Cromie <[email protected]> wrote:
> [...]
> drm_test_buddy_alloc_exceeds_max_order() uses the on a u64 value,
> where they silently truncate the 10GB allocation, giving unexpected
> success in DRM-CI. (see below the snip).
>
> Fix this by replacing the standard macros with safe 64-bit
> power-of-two calculations using ilog2().
This is a general DRM bug, if you send a new iteration, can you move it at
then start so it can be applied easly?
>
>
> diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
> index b27761246d4b..ff158cc1d27e 100644
> --- a/drivers/gpu/buddy.c
> +++ b/drivers/gpu/buddy.c
> @@ -915,7 +915,7 @@ static int __alloc_contig_try_harder(struct gpu_buddy *mm,
> u64 modify_size;
> int err;
>
> - modify_size = rounddown_pow_of_two(size);
> + modify_size = 1ULL << ilog2(size);
Thanks for catching this issue!
To avoid this kind of issue later / in other parts of the kernel, maybe you
can change the macro itself to properly handle u64? I am thinking about
something similar to ilog2[1]:
( \
(sizeof(n) <= 4) ? \
__rounddown_pow_of_two_u32(n) : \
__rounddown_pow_of_two_u64(n) \
)
[1]:https://elixir.bootlin.com/linux/v6.19.8/source/include/linux/log2.h#L156-L164
--
Louis Chauvet <[email protected]>
