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| author | Alexei Starovoitov <ast@kernel.org> | 2024-02-20 15:50:01 -0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2024-02-21 13:49:14 -0800 |
| commit | a3c70a3cf11eb4b6409afc2cce1a3747e1dfe96f (patch) | |
| tree | 5fe7b4c3fc67c958714897ade529227918b1282c /include/linux/bpf.h | |
| parent | 01dbd7d8720a0cc97dad5e70ec674dacdc66cf3c (diff) | |
bpf: Shrink size of struct bpf_map/bpf_array.
Back in 2018 the commit be95a845cc44 ("bpf: avoid false sharing of map refcount
with max_entries") added ____cacheline_aligned to "struct bpf_map" to make sure
that fields like refcnt don't share a cache line with max_entries that is used
to bounds check map access. That was done to make spectre style attacks harder.
The main mitigation is done via code similar to array_index_nospec(), of course.
This was an additional precaution.
It increased the size of "struct bpf_map" a little, but it's affect on all
other maps (like array) is significant, since "struct bpf_map" is typically
the first member in other map types.
Undo this ____cacheline_aligned tag. Instead move freeze_mutex field around, so
that refcnt and max_entries are still in different cache lines.
The main effect is seen in sizeof(struct bpf_array) that reduces from 320
to 248 bytes.
BEFORE:
struct bpf_map {
const struct bpf_map_ops * ops; /* 0 8 */
...
char name[16]; /* 96 16 */
/* XXX 16 bytes hole, try to pack */
/* --- cacheline 2 boundary (128 bytes) --- */
atomic64_t refcnt __attribute__((__aligned__(64))); /* 128 8 */
...
/* size: 256, cachelines: 4, members: 30 */
/* sum members: 232, holes: 1, sum holes: 16 */
/* padding: 8 */
/* paddings: 1, sum paddings: 2 */
} __attribute__((__aligned__(64)));
struct bpf_array {
struct bpf_map map; /* 0 256 */
...
/* size: 320, cachelines: 5, members: 5 */
/* padding: 48 */
/* paddings: 1, sum paddings: 8 */
} __attribute__((__aligned__(64)));
AFTER:
struct bpf_map {
/* size: 232, cachelines: 4, members: 30 */
/* paddings: 1, sum paddings: 2 */
/* last cacheline: 40 bytes */
};
struct bpf_array {
/* size: 248, cachelines: 4, members: 5 */
/* last cacheline: 56 bytes */
};
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240220235001.57411-1-alexei.starovoitov@gmail.com
Diffstat (limited to 'include/linux/bpf.h')
| -rw-r--r-- | include/linux/bpf.h | 12 |
1 files changed, 3 insertions, 9 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index c7aa99b44dbd..814dc913a968 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -251,10 +251,7 @@ struct bpf_list_node_kern { } __attribute__((aligned(8))); struct bpf_map { - /* The first two cachelines with read-mostly members of which some - * are also accessed in fast-path (e.g. ops, max_entries). - */ - const struct bpf_map_ops *ops ____cacheline_aligned; + const struct bpf_map_ops *ops; struct bpf_map *inner_map_meta; #ifdef CONFIG_SECURITY void *security; @@ -276,17 +273,14 @@ struct bpf_map { struct obj_cgroup *objcg; #endif char name[BPF_OBJ_NAME_LEN]; - /* The 3rd and 4th cacheline with misc members to avoid false sharing - * particularly with refcounting. - */ - atomic64_t refcnt ____cacheline_aligned; + struct mutex freeze_mutex; + atomic64_t refcnt; atomic64_t usercnt; /* rcu is used before freeing and work is only used during freeing */ union { struct work_struct work; struct rcu_head rcu; }; - struct mutex freeze_mutex; atomic64_t writecnt; /* 'Ownership' of program-containing map is claimed by the first program * that is going to use this map or by the first program which FD is |