On Thu, 30 Mar 2023, Christian König <christian.koenig@xxxxxxx> wrote: > Am 30.03.23 um 12:53 schrieb Jani Nikula: >> On Wed, 29 Mar 2023, David Gow <davidgow@xxxxxxxxxx> wrote: >>> The drm buddy allocator tests were broken on 32-bit systems, as >>> rounddown_pow_of_two() takes a long, and the buddy allocator handles >>> 64-bit sizes even on 32-bit systems. >>> >>> This can be reproduced with the drm_buddy_allocator KUnit tests on i386: >>> ./tools/testing/kunit/kunit.py run --arch i386 \ >>> --kunitconfig ./drivers/gpu/drm/tests drm_buddy >>> >>> (It results in kernel BUG_ON() when too many blocks are created, due to >>> the block size being too small.) >>> >>> This was independently uncovered (and fixed) by Luís Mendes, whose patch >>> added a new u64 variant of rounddown_pow_of_two(). This version instead >>> recalculates the size based on the order. >>> >>> Reported-by: Luís Mendes <luis.p.mendes@xxxxxxxxx> >>> Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@xxxxxxxxxxxxxx/T/ >>> Signed-off-by: David Gow <davidgow@xxxxxxxxxx> >>> --- >>> drivers/gpu/drm/drm_buddy.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c >>> index 3d1f50f481cf..7098f125b54a 100644 >>> --- a/drivers/gpu/drm/drm_buddy.c >>> +++ b/drivers/gpu/drm/drm_buddy.c >>> @@ -146,8 +146,8 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size) >>> unsigned int order; >>> u64 root_size; >>> >>> - root_size = rounddown_pow_of_two(size); >>> - order = ilog2(root_size) - ilog2(chunk_size); >>> + order = ilog2(size) - ilog2(chunk_size); >>> + root_size = chunk_size << order; >> Just noticed near the beginning of the function there's also: >> >> if (!is_power_of_2(chunk_size)) >> return -EINVAL; >> >> which is also wrong for 32-bit. > > Yeah, but that isn't vital. We just use u64 for the chunk_size for > consistency. > > In reality I wouldn't except more than 256K here. Right. It's just not pedantically correct either. ;) is_power_of_2() is pretty scary as it is, since it just truncates. BR, Jani. > > Regards, > Christian. > >> >> >> BR, >> Jani. >> >> >>> >>> root = drm_block_alloc(mm, NULL, order, offset); >>> if (!root) > -- Jani Nikula, Intel Open Source Graphics Center
