| Message ID | 20201009224007.30447-4-daniel@iogearbox.net |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Follow-up BPF helper improvements | expand |
On Fri, Oct 9, 2020 at 3:40 PM Daniel Borkmann <daniel@iogearbox.net> wrote: > > Recent work in f4d05259213f ("bpf: Add map_meta_equal map ops") and 134fede4eecf > ("bpf: Relax max_entries check for most of the inner map types") added support > for dynamic inner max elements for most map-in-map types. Exceptions were maps > like array or prog array where the map_gen_lookup() callback uses the maps' > max_entries field as a constant when emitting instructions. > > We recently implemented Maglev consistent hashing into Cilium's load balancer > which uses map-in-map with an outer map being hash and inner being array holding > the Maglev backend table for each service. This has been designed this way in > order to reduce overall memory consumption given the outer hash map allows to > avoid preallocating a large, flat memory area for all services. Also, the > number of service mappings is not always known a-priori. > > The use case for dynamic inner array map entries is to further reduce memory > overhead, for example, some services might just have a small number of back > ends while others could have a large number. Right now the Maglev backend table > for small and large number of backends would need to have the same inner array > map entries which adds a lot of unneeded overhead. > > Dynamic inner array map entries can be realized by avoiding the inlined code > generation for their lookup. The lookup will still be efficient since it will > be calling into array_map_lookup_elem() directly and thus avoiding retpoline. > The patch adds a BPF_F_INNER_MAP flag to map creation which therefore skips > inline code generation and relaxes array_map_meta_equal() check to ignore both > maps' max_entries. > > Example code generation where inner map is dynamic sized array: > > # bpftool p d x i 125 > int handle__sys_enter(void * ctx): > ; int handle__sys_enter(void *ctx) > 0: (b4) w1 = 0 > ; int key = 0; > 1: (63) *(u32 *)(r10 -4) = r1 > 2: (bf) r2 = r10 > ; > 3: (07) r2 += -4 > ; inner_map = bpf_map_lookup_elem(&outer_arr_dyn, &key); > 4: (18) r1 = map[id:468] > 6: (07) r1 += 272 > 7: (61) r0 = *(u32 *)(r2 +0) > 8: (35) if r0 >= 0x3 goto pc+5 > 9: (67) r0 <<= 3 > 10: (0f) r0 += r1 > 11: (79) r0 = *(u64 *)(r0 +0) > 12: (15) if r0 == 0x0 goto pc+1 > 13: (05) goto pc+1 > 14: (b7) r0 = 0 > 15: (b4) w6 = -1 > ; if (!inner_map) > 16: (15) if r0 == 0x0 goto pc+6 > 17: (bf) r2 = r10 > ; > 18: (07) r2 += -4 > ; val = bpf_map_lookup_elem(inner_map, &key); > 19: (bf) r1 = r0 | No inlining but instead > 20: (85) call array_map_lookup_elem#149280 | call to array_map_lookup_elem() > ; return val ? *val : -1; | for inner array lookup. > 21: (15) if r0 == 0x0 goto pc+1 > ; return val ? *val : -1; > 22: (61) r6 = *(u32 *)(r0 +0) > ; } > 23: (bc) w0 = w6 > 24: (95) exit > > Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> > Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com> > --- > include/linux/bpf.h | 2 +- > include/uapi/linux/bpf.h | 3 +++ > kernel/bpf/arraymap.c | 17 +++++++++++------ > kernel/bpf/hashtab.c | 6 +++--- > kernel/bpf/verifier.c | 4 +++- > net/xdp/xskmap.c | 2 +- > tools/include/uapi/linux/bpf.h | 3 +++ > 7 files changed, 25 insertions(+), 12 deletions(-) > [...] > *insn++ = BPF_ALU64_IMM(BPF_ADD, map_ptr, offsetof(struct bpf_array, value)); > *insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0); > if (!map->bypass_spec_v1) { > @@ -496,8 +499,10 @@ static int array_map_mmap(struct bpf_map *map, struct vm_area_struct *vma) > static bool array_map_meta_equal(const struct bpf_map *meta0, > const struct bpf_map *meta1) > { > - return meta0->max_entries == meta1->max_entries && > - bpf_map_meta_equal(meta0, meta1); > + if (!bpf_map_meta_equal(meta0, meta1)) > + return false; > + return meta0->map_flags & BPF_F_INNER_MAP ? true : > + meta0->max_entries == meta1->max_entries; even if meta1 doesn't have BPF_F_INNER_MAP, it's ok, because all the accesses for map returned from outer map lookup will not inline, is that right? So this flag only matters for the inner map's prototype. You also mentioned that not inlining array access should still be fast. So I wonder, what if we just force non-inlined access for inner maps of ARRAY type? Would it be too bad of a hit for existing applications? The benefit would be that everything would just work without a special flag. If perf hit isn't prohibitive, it might be worthwhile to simplify user experience? > } > > struct bpf_iter_seq_array_map_info { > @@ -1251,7 +1256,7 @@ static void *array_of_map_lookup_elem(struct bpf_map *map, void *key) > return READ_ONCE(*inner_map); > } > [...] > struct bpf_insn *insn = insn_buf; > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index f3e36eade3d4..76d43ef60e7b 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -11049,6 +11049,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) > if (insn->imm == BPF_FUNC_map_lookup_elem && > ops->map_gen_lookup) { > cnt = ops->map_gen_lookup(map_ptr, insn_buf); > + if (cnt == -EOPNOTSUPP) > + goto patch_map_ops_generic; > if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) { should this now check cnt <= 0 instead? > verbose(env, "bpf verifier is misconfigured\n"); > return -EINVAL; > @@ -11079,7 +11081,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) > (int (*)(struct bpf_map *map, void *value))NULL)); > BUILD_BUG_ON(!__same_type(ops->map_peek_elem, > (int (*)(struct bpf_map *map, void *value))NULL)); > - > +patch_map_ops_generic: > switch (insn->imm) { > case BPF_FUNC_map_lookup_elem: > insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) - [...]
On 10/10/20 1:01 AM, Andrii Nakryiko wrote: > On Fri, Oct 9, 2020 at 3:40 PM Daniel Borkmann <daniel@iogearbox.net> wrote: [...] >> *insn++ = BPF_ALU64_IMM(BPF_ADD, map_ptr, offsetof(struct bpf_array, value)); >> *insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0); >> if (!map->bypass_spec_v1) { >> @@ -496,8 +499,10 @@ static int array_map_mmap(struct bpf_map *map, struct vm_area_struct *vma) >> static bool array_map_meta_equal(const struct bpf_map *meta0, >> const struct bpf_map *meta1) >> { >> - return meta0->max_entries == meta1->max_entries && >> - bpf_map_meta_equal(meta0, meta1); >> + if (!bpf_map_meta_equal(meta0, meta1)) >> + return false; >> + return meta0->map_flags & BPF_F_INNER_MAP ? true : >> + meta0->max_entries == meta1->max_entries; > > even if meta1 doesn't have BPF_F_INNER_MAP, it's ok, because all the > accesses for map returned from outer map lookup will not inline, is > that right? So this flag only matters for the inner map's prototype. Not right now, we would have to open code bpf_map_meta_equal() to cut out that bit from the meta0/1 flags comparison. I wouldn't change bpf_map_meta_equal() itself given that bit can be reused for different purpose for other map types. > You also mentioned that not inlining array access should still be > fast. So I wonder, what if we just force non-inlined access for inner > maps of ARRAY type? Would it be too bad of a hit for existing > applications? Fast in the sense of that we can avoid a retpoline given the direct call to array_map_lookup_elem() as opposed to bpf_map_lookup_elem(). In the array_map_gen_lookup() we even have insn level optimizations such as replacing BPF_MUL with BPF_LSH with immediate elem size on power of 2 #elems as well as avoiding spectre masking (which the call one has not), presumably for cases like XDP we might want the best implementation if usage allows it. > The benefit would be that everything would just work without a special > flag. If perf hit isn't prohibitive, it might be worthwhile to > simplify user experience? Taking the above penalty aside for same sized-elems, simplest one would have been to just set inner_map_meta->ops to &array_map_no_inline_ops inside the bpf_map_meta_alloc().
On Fri, Oct 9, 2020 at 5:10 PM Daniel Borkmann <daniel@iogearbox.net> wrote: > > On 10/10/20 1:01 AM, Andrii Nakryiko wrote: > > On Fri, Oct 9, 2020 at 3:40 PM Daniel Borkmann <daniel@iogearbox.net> wrote: > [...] > >> *insn++ = BPF_ALU64_IMM(BPF_ADD, map_ptr, offsetof(struct bpf_array, value)); > >> *insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0); > >> if (!map->bypass_spec_v1) { > >> @@ -496,8 +499,10 @@ static int array_map_mmap(struct bpf_map *map, struct vm_area_struct *vma) > >> static bool array_map_meta_equal(const struct bpf_map *meta0, > >> const struct bpf_map *meta1) > >> { > >> - return meta0->max_entries == meta1->max_entries && > >> - bpf_map_meta_equal(meta0, meta1); > >> + if (!bpf_map_meta_equal(meta0, meta1)) > >> + return false; > >> + return meta0->map_flags & BPF_F_INNER_MAP ? true : > >> + meta0->max_entries == meta1->max_entries; > > > > even if meta1 doesn't have BPF_F_INNER_MAP, it's ok, because all the > > accesses for map returned from outer map lookup will not inline, is > > that right? So this flag only matters for the inner map's prototype. > > Not right now, we would have to open code bpf_map_meta_equal() to cut out that > bit from the meta0/1 flags comparison. I wouldn't change bpf_map_meta_equal() > itself given that bit can be reused for different purpose for other map types. > > > You also mentioned that not inlining array access should still be > > fast. So I wonder, what if we just force non-inlined access for inner > > maps of ARRAY type? Would it be too bad of a hit for existing > > applications? > > Fast in the sense of that we can avoid a retpoline given the direct call Ah, ok, then probably an extra flag is necessary. > to array_map_lookup_elem() as opposed to bpf_map_lookup_elem(). In the > array_map_gen_lookup() we even have insn level optimizations such as > replacing BPF_MUL with BPF_LSH with immediate elem size on power of 2 > #elems as well as avoiding spectre masking (which the call one has not), > presumably for cases like XDP we might want the best implementation if > usage allows it. > > > The benefit would be that everything would just work without a special > > flag. If perf hit isn't prohibitive, it might be worthwhile to > > simplify user experience? > > Taking the above penalty aside for same sized-elems, simplest one would have > been to just set inner_map_meta->ops to &array_map_no_inline_ops inside the > bpf_map_meta_alloc().
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index dc63eeed4fd9..2b16bf48aab6 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -82,7 +82,7 @@ struct bpf_map_ops { void *(*map_fd_get_ptr)(struct bpf_map *map, struct file *map_file, int fd); void (*map_fd_put_ptr)(void *ptr); - u32 (*map_gen_lookup)(struct bpf_map *map, struct bpf_insn *insn_buf); + int (*map_gen_lookup)(struct bpf_map *map, struct bpf_insn *insn_buf); u32 (*map_fd_sys_lookup_elem)(void *ptr); void (*map_seq_show_elem)(struct bpf_map *map, void *key, struct seq_file *m); diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index b97bc5abb3b8..bf5a99d803e4 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -435,6 +435,9 @@ enum { /* Share perf_event among processes */ BPF_F_PRESERVE_ELEMS = (1U << 11), + +/* Create a map that is suitable to be an inner map with dynamic max entries */ + BPF_F_INNER_MAP = (1U << 12), }; /* Flags for BPF_PROG_QUERY. */ diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index bd777dd6f967..c6c81eceb68f 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -16,7 +16,7 @@ #define ARRAY_CREATE_FLAG_MASK \ (BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK | \ - BPF_F_PRESERVE_ELEMS) + BPF_F_PRESERVE_ELEMS | BPF_F_INNER_MAP) static void bpf_array_free_percpu(struct bpf_array *array) { @@ -62,7 +62,7 @@ int array_map_alloc_check(union bpf_attr *attr) return -EINVAL; if (attr->map_type != BPF_MAP_TYPE_ARRAY && - attr->map_flags & BPF_F_MMAPABLE) + attr->map_flags & (BPF_F_MMAPABLE | BPF_F_INNER_MAP)) return -EINVAL; if (attr->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY && @@ -214,7 +214,7 @@ static int array_map_direct_value_meta(const struct bpf_map *map, u64 imm, } /* emit BPF instructions equivalent to C code of array_map_lookup_elem() */ -static u32 array_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) +static int array_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) { struct bpf_array *array = container_of(map, struct bpf_array, map); struct bpf_insn *insn = insn_buf; @@ -223,6 +223,9 @@ static u32 array_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) const int map_ptr = BPF_REG_1; const int index = BPF_REG_2; + if (map->map_flags & BPF_F_INNER_MAP) + return -EOPNOTSUPP; + *insn++ = BPF_ALU64_IMM(BPF_ADD, map_ptr, offsetof(struct bpf_array, value)); *insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0); if (!map->bypass_spec_v1) { @@ -496,8 +499,10 @@ static int array_map_mmap(struct bpf_map *map, struct vm_area_struct *vma) static bool array_map_meta_equal(const struct bpf_map *meta0, const struct bpf_map *meta1) { - return meta0->max_entries == meta1->max_entries && - bpf_map_meta_equal(meta0, meta1); + if (!bpf_map_meta_equal(meta0, meta1)) + return false; + return meta0->map_flags & BPF_F_INNER_MAP ? true : + meta0->max_entries == meta1->max_entries; } struct bpf_iter_seq_array_map_info { @@ -1251,7 +1256,7 @@ static void *array_of_map_lookup_elem(struct bpf_map *map, void *key) return READ_ONCE(*inner_map); } -static u32 array_of_map_gen_lookup(struct bpf_map *map, +static int array_of_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) { struct bpf_array *array = container_of(map, struct bpf_array, map); diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 3395cf140d22..1815e97d4c9c 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -612,7 +612,7 @@ static void *htab_map_lookup_elem(struct bpf_map *map, void *key) * bpf_prog * __htab_map_lookup_elem */ -static u32 htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) +static int htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) { struct bpf_insn *insn = insn_buf; const int ret = BPF_REG_0; @@ -651,7 +651,7 @@ static void *htab_lru_map_lookup_elem_sys(struct bpf_map *map, void *key) return __htab_lru_map_lookup_elem(map, key, false); } -static u32 htab_lru_map_gen_lookup(struct bpf_map *map, +static int htab_lru_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) { struct bpf_insn *insn = insn_buf; @@ -2070,7 +2070,7 @@ static void *htab_of_map_lookup_elem(struct bpf_map *map, void *key) return READ_ONCE(*inner_map); } -static u32 htab_of_map_gen_lookup(struct bpf_map *map, +static int htab_of_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) { struct bpf_insn *insn = insn_buf; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f3e36eade3d4..76d43ef60e7b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11049,6 +11049,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) if (insn->imm == BPF_FUNC_map_lookup_elem && ops->map_gen_lookup) { cnt = ops->map_gen_lookup(map_ptr, insn_buf); + if (cnt == -EOPNOTSUPP) + goto patch_map_ops_generic; if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) { verbose(env, "bpf verifier is misconfigured\n"); return -EINVAL; @@ -11079,7 +11081,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) (int (*)(struct bpf_map *map, void *value))NULL)); BUILD_BUG_ON(!__same_type(ops->map_peek_elem, (int (*)(struct bpf_map *map, void *value))NULL)); - +patch_map_ops_generic: switch (insn->imm) { case BPF_FUNC_map_lookup_elem: insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) - diff --git a/net/xdp/xskmap.c b/net/xdp/xskmap.c index 0c5df593bc56..49da2b8ace8b 100644 --- a/net/xdp/xskmap.c +++ b/net/xdp/xskmap.c @@ -132,7 +132,7 @@ static int xsk_map_get_next_key(struct bpf_map *map, void *key, void *next_key) return 0; } -static u32 xsk_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) +static int xsk_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf) { const int ret = BPF_REG_0, mp = BPF_REG_1, index = BPF_REG_2; struct bpf_insn *insn = insn_buf; diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index b97bc5abb3b8..bf5a99d803e4 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -435,6 +435,9 @@ enum { /* Share perf_event among processes */ BPF_F_PRESERVE_ELEMS = (1U << 11), + +/* Create a map that is suitable to be an inner map with dynamic max entries */ + BPF_F_INNER_MAP = (1U << 12), }; /* Flags for BPF_PROG_QUERY. */
Recent work in f4d05259213f ("bpf: Add map_meta_equal map ops") and 134fede4eecf ("bpf: Relax max_entries check for most of the inner map types") added support for dynamic inner max elements for most map-in-map types. Exceptions were maps like array or prog array where the map_gen_lookup() callback uses the maps' max_entries field as a constant when emitting instructions. We recently implemented Maglev consistent hashing into Cilium's load balancer which uses map-in-map with an outer map being hash and inner being array holding the Maglev backend table for each service. This has been designed this way in order to reduce overall memory consumption given the outer hash map allows to avoid preallocating a large, flat memory area for all services. Also, the number of service mappings is not always known a-priori. The use case for dynamic inner array map entries is to further reduce memory overhead, for example, some services might just have a small number of back ends while others could have a large number. Right now the Maglev backend table for small and large number of backends would need to have the same inner array map entries which adds a lot of unneeded overhead. Dynamic inner array map entries can be realized by avoiding the inlined code generation for their lookup. The lookup will still be efficient since it will be calling into array_map_lookup_elem() directly and thus avoiding retpoline. The patch adds a BPF_F_INNER_MAP flag to map creation which therefore skips inline code generation and relaxes array_map_meta_equal() check to ignore both maps' max_entries. Example code generation where inner map is dynamic sized array: # bpftool p d x i 125 int handle__sys_enter(void * ctx): ; int handle__sys_enter(void *ctx) 0: (b4) w1 = 0 ; int key = 0; 1: (63) *(u32 *)(r10 -4) = r1 2: (bf) r2 = r10 ; 3: (07) r2 += -4 ; inner_map = bpf_map_lookup_elem(&outer_arr_dyn, &key); 4: (18) r1 = map[id:468] 6: (07) r1 += 272 7: (61) r0 = *(u32 *)(r2 +0) 8: (35) if r0 >= 0x3 goto pc+5 9: (67) r0 <<= 3 10: (0f) r0 += r1 11: (79) r0 = *(u64 *)(r0 +0) 12: (15) if r0 == 0x0 goto pc+1 13: (05) goto pc+1 14: (b7) r0 = 0 15: (b4) w6 = -1 ; if (!inner_map) 16: (15) if r0 == 0x0 goto pc+6 17: (bf) r2 = r10 ; 18: (07) r2 += -4 ; val = bpf_map_lookup_elem(inner_map, &key); 19: (bf) r1 = r0 | No inlining but instead 20: (85) call array_map_lookup_elem#149280 | call to array_map_lookup_elem() ; return val ? *val : -1; | for inner array lookup. 21: (15) if r0 == 0x0 goto pc+1 ; return val ? *val : -1; 22: (61) r6 = *(u32 *)(r0 +0) ; } 23: (bc) w0 = w6 24: (95) exit Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com> --- include/linux/bpf.h | 2 +- include/uapi/linux/bpf.h | 3 +++ kernel/bpf/arraymap.c | 17 +++++++++++------ kernel/bpf/hashtab.c | 6 +++--- kernel/bpf/verifier.c | 4 +++- net/xdp/xskmap.c | 2 +- tools/include/uapi/linux/bpf.h | 3 +++ 7 files changed, 25 insertions(+), 12 deletions(-)