[RFC v2 PATCH bpf-next 1/4] bpf: add percpu stats for bpf_map elements insertions/deletions

Anton Protopopov
2023-06-22T09:52:38Z

Add a generic percpu stats for bpf_map elements insertions/deletions in order
to keep track of both, the current (approximate) number of elements in a map
and per-cpu statistics on update/delete operations.

To expose these stats a particular map implementation should initialize the
counter and adjust it as needed using the 'bpf_map_*_elements_counter' helpers
provided by this commit. The counter can be read by an iterator program.

A bpf_map_sum_elements_counter kfunc was added to simplify getting the sum of
the per-cpu values. If a map doesn't implement the counter, then it will always
return 0.

Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
---
include/linux/bpf.h | 30 +++++++++++++++++++++++++++
kernel/bpf/map_iter.c | 48 ++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f58895830ada..20292a096188 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -275,6 +275,7 @@ struct bpf_map {
} owner;
bool bypass_spec_v1;
bool frozen; /* write-once; write-protected by freeze_mutex */
+ s64 __percpu *elements_count;
};

static inline const char *btf_field_type_name(enum btf_field_type type)
@@ -2040,6 +2041,35 @@ bpf_map_alloc_percpu(const struct bpf_map *map, size_t size, size_t align,
}
#endif

+static inline int
+bpf_map_init_elements_counter(struct bpf_map *map)
+{
+ size_t size = sizeof(*map->elements_count), align = size;
+ gfp_t flags = GFP_USER | __GFP_NOWARN;
+
+ map->elements_count = bpf_map_alloc_percpu(map, size, align, flags);
+ if (!map->elements_count)
+ return -ENOMEM;
+
+ return 0;
+}
+
+static inline void
+bpf_map_free_elements_counter(struct bpf_map *map)
+{
+ free_percpu(map->elements_count);
+}
+
+static inline void bpf_map_inc_elements_counter(struct bpf_map *map)
+{
+ this_cpu_inc(*map->elements_count);
+}
+
+static inline void bpf_map_dec_elements_counter(struct bpf_map *map)
+{
+ this_cpu_dec(*map->elements_count);
+}
+
extern int sysctl_unprivileged_bpf_disabled;

static inline bool bpf_allow_ptr_leaks(void)
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index b0fa190b0979..26ca00dde962 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -93,7 +93,7 @@ static struct bpf_iter_reg bpf_map_reg_info = {
.ctx_arg_info_size = 1,
.ctx_arg_info = {
{ offsetof(struct bpf_iter__bpf_map, map),
- PTR_TO_BTF_ID_OR_NULL },
+ PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
},
.seq_info = &bpf_map_seq_info,
};
@@ -193,3 +193,49 @@ static int __init bpf_map_iter_init(void)
}

late_initcall(bpf_map_iter_init);
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global functions as their definitions will be in vmlinux BTF");
+
+__bpf_kfunc s64 bpf_map_sum_elements_counter(struct bpf_map *map)
+{
+ s64 *pcount;
+ s64 ret = 0;
+ int cpu;
+
+ if (!map || !map->elements_count)
+ return 0;
+
+ for_each_possible_cpu(cpu) {
+ pcount = per_cpu_ptr(map->elements_count, cpu);
+ ret += READ_ONCE(*pcount);
+ }
+ return ret;
+}
+
+__diag_pop();
+
+BTF_SET8_START(bpf_map_iter_kfunc_ids)
+BTF_ID_FLAGS(func, bpf_map_sum_elements_counter, KF_TRUSTED_ARGS)
+BTF_SET8_END(bpf_map_iter_kfunc_ids)
+
+static int tracing_iter_filter(const struct bpf_prog *prog, u32 kfunc_id)
+{
+ if (btf_id_set8_contains(&bpf_map_iter_kfunc_ids, kfunc_id) &&
+ prog->expected_attach_type != BPF_TRACE_ITER)
+ return -EACCES;
+ return 0;
+}
+
+static const struct btf_kfunc_id_set bpf_map_iter_kfunc_set = {
+ .owner = THIS_MODULE,
+ .set = &bpf_map_iter_kfunc_ids,
+ .filter = tracing_iter_filter,
+};
+
+static int init_subsystem(void)
+{
+ return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_map_iter_kfunc_set);
+}
+late_initcall(init_subsystem);
--
2.34.1