From: Hou Tao <houtao1@xxxxxxxxxx>
Commit d52b59315bf5 ("bpf: Adjust size_index according to the value of
KMALLOC_MIN_SIZE") uses KMALLOC_MIN_SIZE to adjust size_index, but as
reported by Nathan, the adjustment is not enough, because
__kmalloc_minalign() also decides the minimal alignment of slab object
as shown in new_kmalloc_cache() and its value may be greater than
KMALLOC_MIN_SIZE (e.g., 64 bytes vs 8 bytes under a riscv QEMU VM).
Instead of invoking __kmalloc_minalign() in bpf subsystem to find the
maximal alignment, just using kmalloc_size_roundup() directly to get the
corresponding slab object size for each allocation size. If these two
sizes are unmatched, adjust size_index to select a bpf_mem_cache with
unit_size equal to the object_size of the underlying slab cache for the
allocation size.
Fixes: 822fb26bdb55 ("bpf: Add a hint to allocated objects.")
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Closes: https://lore.kernel.org/bpf/20230914181407.GA1000274@dev-arch.thelio-3990X/
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
kernel/bpf/memalloc.c | 44 +++++++++++++++++++------------------------
1 file changed, 19 insertions(+), 25 deletions(-)
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 1c22b90e754a..06fbb5168482 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -958,37 +958,31 @@ void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags)
return !ret ? NULL : ret + LLIST_NODE_SZ;
}
-/* Most of the logic is taken from setup_kmalloc_cache_index_table() */
static __init int bpf_mem_cache_adjust_size(void)
{
- unsigned int size, index;
+ unsigned int size;
- /* Normally KMALLOC_MIN_SIZE is 8-bytes, but it can be
- * up-to 256-bytes.
+ /* Adjusting the indexes in size_index() according to the object_size
+ * of underlying slab cache, so bpf_mem_alloc() will select a
+ * bpf_mem_cache with unit_size equal to the object_size of
+ * the underlying slab cache.
+ *
+ * The maximal value of KMALLOC_MIN_SIZE and __kmalloc_minalign() is
+ * 256-bytes, so only do adjustment for [8-bytes, 192-bytes].
*/
- size = KMALLOC_MIN_SIZE;
- if (size <= 192)
- index = size_index[(size - 1) / 8];
- else
- index = fls(size - 1) - 1;
- for (size = 8; size < KMALLOC_MIN_SIZE && size <= 192; size += 8)
- size_index[(size - 1) / 8] = index;
+ for (size = 192; size >= 8; size -= 8) {
+ unsigned int kmalloc_size, index;
- /* The minimal alignment is 64-bytes, so disable 96-bytes cache and
- * use 128-bytes cache instead.
- */
- if (KMALLOC_MIN_SIZE >= 64) {
- index = size_index[(128 - 1) / 8];
- for (size = 64 + 8; size <= 96; size += 8)
- size_index[(size - 1) / 8] = index;
- }
+ kmalloc_size = kmalloc_size_roundup(size);
+ if (kmalloc_size == size)
+ continue;
- /* The minimal alignment is 128-bytes, so disable 192-bytes cache and
- * use 256-bytes cache instead.
- */
- if (KMALLOC_MIN_SIZE >= 128) {
- index = fls(256 - 1) - 1;
- for (size = 128 + 8; size <= 192; size += 8)
+ if (kmalloc_size <= 192)
+ index = size_index[(kmalloc_size - 1) / 8];
+ else
+ index = fls(kmalloc_size - 1) - 1;
+ /* Only overwrite if necessary */
+ if (size_index[(size - 1) / 8] != index)
size_index[(size - 1) / 8] = index;
}
--
2.29.2
