[PATCH AUTOSEL 6.2 11/17] drm: buddy_allocator: Fix buddy allocator init on 32-bit systems

[Sasha Levin]

From: David Gow <davidgow@xxxxxxxxxx>

[ Upstream commit 4453545b5b4c3eff941f69a5530f916d899db025 ]

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>
Acked-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Arunpravin Paneer Selvam <arunpravin.paneerselvam@xxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20230329065532.2122295-1-davidgow@xxxxxxxxxx
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@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 3d1f50f481cfd..7098f125b54a9 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;
 
 		root = drm_block_alloc(mm, NULL, order, offset);
 		if (!root)
-- 
2.39.2