In lock_region, simplify the calculation of the region_width parameter.
This field is the size, but encoded as log2(ceil(size)) - 1.
log2(ceil(size)) may be computed directly as fls(size - 1). However, we
want to use the 64-bit versions as the amount to lock can exceed
32-bits.
This avoids undefined behaviour when locking all memory (size ~0),
caught by UBSAN.
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzw...@collabora.com>
Reported-and-tested-by: Chris Morgan <macromor...@hotmail.com>
Cc: <sta...@vger.kernel.org>
---
drivers/gpu/drm/panfrost/panfrost_mmu.c | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 0da5b3100ab1..f6e02d0392f4 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -62,21 +62,12 @@ static void lock_region(struct panfrost_device *pfdev, u32
as_nr,
{
u8 region_width;
u64 region = iova & PAGE_MASK;
- /*
- * fls returns:
- * 1 .. 32
- *
- * 10 + fls(num_pages)
- * results in the range (11 .. 42)
- */
-
- size = round_up(size, PAGE_SIZE);
- region_width = 10 + fls(size >> PAGE_SHIFT);
- if ((size >> PAGE_SHIFT) != (1ul << (region_width - 11))) {
- /* not pow2, so must go up to the next pow2 */
- region_width += 1;
- }
+ /* The size is encoded as ceil(log2) minus(1), which may be calculated
+ * with fls. The size must be clamped to hardware bounds.
+ */
+ size = max_t(u64, size, PAGE_SIZE);
+ region_width = fls64(size - 1) - 1;
region |= region_width;
/* Lock the region that needs to be updated */
--
2.30.2
