Hou Tao wrote:
> 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.
I applied this to 6.6-rc3 and it fixes the warning on my Nezha board (Allwinner
D1) and also boots fine on my VisionFive 2 (JH7110) which didn't show the error
before. I didn't do any other testing beyond that though, but for basic boot
testing:
Tested-by: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
> 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;
> }
>
