Hi,
On 12/13/2023 6:31 AM, Yonghong Song wrote:
> For percpu data structure allocation with bpf_global_percpu_ma,
> the maximum data size is 4K. But for a system with large
> number of cpus, bigger data size (e.g., 2K, 4K) might consume
> a lot of memory. For example, the percpu memory consumption
> with unit size 2K and 1024 cpus will be 2K * 1K * 1k = 2GB
> memory.
>
> We should discourage such usage. Let us limit the maximum data
> size to be 512 for bpf_global_percpu_ma allocation.
>
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 0c55fe4451e1..e5cb6b7526b6 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -43,6 +43,8 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
> };
>
> struct bpf_mem_alloc bpf_global_percpu_ma;
> +#define LLIST_NODE_SZ sizeof(struct llist_node)
> +#define BPF_GLOBAL_PERCPU_MA_MAX_SIZE (512 - LLIST_NODE_SZ)
It seems for per-cpu allocation the extra subtraction is not needed, we
could use all allocated space in per-cpu pointer. Maybe we could update
bpf_mem_alloc() firstly to use size instead of size + sizeof(void *) to
select cache.
>
> /* bpf_check() is a static code analyzer that walks eBPF program
> * instruction by instruction and updates register/stack state.
> @@ -12091,6 +12093,11 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> }
>
> if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
> + if (ret_t->size > BPF_GLOBAL_PERCPU_MA_MAX_SIZE) {
> + verbose(env, "bpf_percpu_obj_new type size (%d) is greater than %lu\n",
> + ret_t->size, BPF_GLOBAL_PERCPU_MA_MAX_SIZE);
> + return -EINVAL;
> + }
> mutex_lock(&bpf_percpu_ma_lock);
> err = bpf_mem_alloc_percpu_unit_init(&bpf_global_percpu_ma, ret_t->size);
> mutex_unlock(&bpf_percpu_ma_lock);
