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While some of the BPF map lookup helpers provide a ->map_gen_lookup()
callback for inlining the map lookup altogether it is not available
for every map, so the remaining ones have to call bpf_map_lookup_elem()
helper which does a dispatch to map->ops->map_lookup_elem(). In
times of retpolines, this will control and trap speculative execution
rather than letting it do its work for the indirect call and will
therefore cause a slowdown. Likewise, bpf_map_update_elem() and
bpf_map_delete_elem() do not have an inlined version and need to call
into their map->ops->map_update_elem() resp. map->ops->map_delete_elem()
handlers.
Before:
# bpftool prog dump xlated id 1
0: (bf) r2 = r10
1: (07) r2 += -8
2: (7a) *(u64 *)(r2 +0) = 0
3: (18) r1 = map[id:1]
5: (85) call __htab_map_lookup_elem#232656
6: (15) if r0 == 0x0 goto pc+4
7: (71) r1 = *(u8 *)(r0 +35)
8: (55) if r1 != 0x0 goto pc+1
9: (72) *(u8 *)(r0 +35) = 1
10: (07) r0 += 56
11: (15) if r0 == 0x0 goto pc+4
12: (bf) r2 = r0
13: (18) r1 = map[id:1]
15: (85) call bpf_map_delete_elem#215008 <-- indirect call via
16: (95) exit helper
After:
# bpftool prog dump xlated id 1
0: (bf) r2 = r10
1: (07) r2 += -8
2: (7a) *(u64 *)(r2 +0) = 0
3: (18) r1 = map[id:1]
5: (85) call __htab_map_lookup_elem#233328
6: (15) if r0 == 0x0 goto pc+4
7: (71) r1 = *(u8 *)(r0 +35)
8: (55) if r1 != 0x0 goto pc+1
9: (72) *(u8 *)(r0 +35) = 1
10: (07) r0 += 56
11: (15) if r0 == 0x0 goto pc+4
12: (bf) r2 = r0
13: (18) r1 = map[id:1]
15: (85) call htab_lru_map_delete_elem#238240 <-- direct call
16: (95) exit
In all three lookup/update/delete cases however we can use the actual
address of the map callback directly if we find that there's only a
single path with a map pointer leading to the helper call, meaning
when the map pointer has not been poisoned from verifier side.
Example code can be seen above for the delete case.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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|---|---|---|
| .. | ||
| arraymap.c | ||
| bpf_lru_list.c | ||
| bpf_lru_list.h | ||
| btf.c | ||
| cgroup.c | ||
| core.c | ||
| cpumap.c | ||
| devmap.c | ||
| disasm.c | ||
| disasm.h | ||
| hashtab.c | ||
| helpers.c | ||
| inode.c | ||
| lpm_trie.c | ||
| Makefile | ||
| map_in_map.c | ||
| map_in_map.h | ||
| offload.c | ||
| percpu_freelist.c | ||
| percpu_freelist.h | ||
| sockmap.c | ||
| stackmap.c | ||
| syscall.c | ||
| tnum.c | ||
| verifier.c | ||
| xskmap.c | ||