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Date: Thu, 14 Dec 2023 22:51:56 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: thinker.li@...il.com
Cc: sinquersw@...il.com, kuifeng@...a.com, netdev@...r.kernel.org,
bpf@...r.kernel.org, ast@...nel.org, song@...nel.org, kernel-team@...a.com,
andrii@...nel.org, drosen@...gle.com
Subject: Re: [PATCH bpf-next v13 10/14] bpf, net: switch to dynamic
registration
On 12/8/23 4:27 PM, thinker.li@...il.com wrote:
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 7384806ee74e..c881befa35f5 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1698,7 +1698,6 @@ struct bpf_struct_ops_desc {
> #if defined(CONFIG_BPF_JIT) && defined(CONFIG_BPF_SYSCALL)
> #define BPF_MODULE_OWNER ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA))
> const struct bpf_struct_ops_desc *bpf_struct_ops_find(struct btf *btf, u32 type_id);
> -void bpf_struct_ops_init(struct btf *btf, struct bpf_verifier_log *log);
> bool bpf_struct_ops_get(const void *kdata);
> void bpf_struct_ops_put(const void *kdata);
> int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
> @@ -1744,10 +1743,6 @@ static inline const struct bpf_struct_ops_desc *bpf_struct_ops_find(struct btf *
> {
> return NULL;
> }
> -static inline void bpf_struct_ops_init(struct btf *btf,
> - struct bpf_verifier_log *log)
> -{
> -}
> static inline bool bpf_try_module_get(const void *data, struct module *owner)
> {
> return try_module_get(owner);
> @@ -3321,6 +3316,14 @@ static inline bool bpf_is_subprog(const struct bpf_prog *prog)
> return prog->aux->func_idx != 0;
> }
>
> +int register_bpf_struct_ops(struct bpf_struct_ops *st_ops);
This probably should be in btf.h like register_btf_kfunc_id_set().
and should have an empty implementation when CONFIG_BPF_SYSCALL is not set.
> +
> +#define REGISTER_BPF_STRUCT_OPS(st_ops, type) \
Add comment here to suggest the module writer to use REGISTER_BPF_STRUCT_OPS
instead of register_bpf_struct_ops().
> +({ \
> + BTF_STRUCT_OPS_TYPE_EMIT(type); \
Directly use BTF_TYPE_EMIT(struct bpf_struct_ops_##type) here.
Also, is it possible to do the DEFINE_STRUCT_OPS_VALUE_TYPE() type here such
that the module writer does not need to. It will be nice if
REGISTER_BPF_STRUCT_OPS does the define value type and emit value type together.
> + register_bpf_struct_ops(st_ops); \
> +})
> +
> enum bpf_struct_ops_state {
> BPF_STRUCT_OPS_STATE_INIT,
> BPF_STRUCT_OPS_STATE_INUSE,
> @@ -3333,4 +3336,19 @@ struct bpf_struct_ops_common_value {
> enum bpf_struct_ops_state state;
> };
>
> +/* bpf_struct_ops_##_name (e.g. bpf_struct_ops_tcp_congestion_ops) is
> + * the map's value exposed to the userspace and its btf-type-id is
> + * stored at the map->btf_vmlinux_value_type_id.
> + *
> + */
> +#define DEFINE_STRUCT_OPS_VALUE_TYPE(_name) \
> +struct bpf_struct_ops_##_name { \
> + struct bpf_struct_ops_common_value common; \
> + struct _name data ____cacheline_aligned_in_smp; \
> +}
> +
> +int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
> + struct btf *btf,
> + struct bpf_verifier_log *log);
> +
nit. same as the comment in previous patch 8. Move these up closer to other
struct_ops structs and functions. bpf_struct_ops_desc_init is implemented in
bpf_struct_ops.c and it should be in the same CONFIG_BPF_JIT guard earlier in
this file. Also, where is the empty bpf_struct_ops_desc_init() when
CONFIG_BPF_JIT is not set?
> #endif /* _LINUX_BPF_H */
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index e2f4b85cf82a..cabab3db5216 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -12,6 +12,8 @@
> #include <uapi/linux/bpf.h>
>
> #define BTF_TYPE_EMIT(type) ((void)(type *)0)
> +#define BTF_STRUCT_OPS_TYPE_EMIT(type) \
> + ((void)(struct bpf_struct_ops_##type *)0)
Remove this new macro. It is almost the same as BTF_TYPE_EMIT and it is only
used once in REGISTER_BPF_STRUCT_OPS. module writer will use
REGISTER_BPF_STRUCT_OPS and no need to figure out what type needs to be emitted.
> #define BTF_TYPE_EMIT_ENUM(enum_val) ((void)enum_val)
>
> /* These need to be macros, as the expressions are used in assembler input */
[ ... ]
> static const struct bpf_struct_ops_desc *
> bpf_struct_ops_find_value(struct btf *btf, u32 value_id)
> {
> + const struct bpf_struct_ops_desc *st_ops_list;
> unsigned int i;
> + u32 cnt = 0;
>
> - if (!value_id || !btf)
> + if (!value_id)
> return NULL;
>
> - for (i = 0; i < ARRAY_SIZE(bpf_struct_ops); i++) {
> - if (bpf_struct_ops[i].value_id == value_id)
> - return &bpf_struct_ops[i];
> + st_ops_list = btf_get_struct_ops(btf, &cnt);
> + for (i = 0; i < cnt; i++) {
> + if (st_ops_list[i].value_id == value_id)
> + return &st_ops_list[i];
> }
>
> return NULL;
> @@ -266,14 +227,17 @@ bpf_struct_ops_find_value(struct btf *btf, u32 value_id)
> const struct bpf_struct_ops_desc *
> bpf_struct_ops_find(struct btf *btf, u32 type_id)
> {
> + const struct bpf_struct_ops_desc *st_ops_list;
> unsigned int i;
> + u32 cnt;
cnt is not initialized here. The above bpf_struct_ops_find_value() did init cnt
to 0 though.
>
> - if (!type_id || !btf)
> + if (!type_id)
> return NULL;
>
> - for (i = 0; i < ARRAY_SIZE(bpf_struct_ops); i++) {
> - if (bpf_struct_ops[i].type_id == type_id)
> - return &bpf_struct_ops[i];
> + st_ops_list = btf_get_struct_ops(btf, &cnt);
> + for (i = 0; i < cnt; i++) {
If st_ops_list is NULL, cnt could be anything here. Lets fix patch 4 to set cnt
to 0 when btf->struct_ops_tab is empty.
> + if (st_ops_list[i].type_id == type_id)
> + return &st_ops_list[i];
> }
>
> return NULL;
> diff --git a/kernel/bpf/bpf_struct_ops_types.h b/kernel/bpf/bpf_struct_ops_types.h
> deleted file mode 100644
> index 5678a9ddf817..000000000000
> --- a/kernel/bpf/bpf_struct_ops_types.h
> +++ /dev/null
> @@ -1,12 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> -/* internal file - do not include directly */
> -
> -#ifdef CONFIG_BPF_JIT
> -#ifdef CONFIG_NET
> -BPF_STRUCT_OPS_TYPE(bpf_dummy_ops)
> -#endif
> -#ifdef CONFIG_INET
> -#include <net/tcp.h>
> -BPF_STRUCT_OPS_TYPE(tcp_congestion_ops)
> -#endif
> -#endif
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index edbe3cbf2dcc..5545dee3ff54 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -19,6 +19,7 @@
> #include <linux/bpf_verifier.h>
> #include <linux/btf.h>
> #include <linux/btf_ids.h>
> +#include <linux/bpf.h>
> #include <linux/bpf_lsm.h>
> #include <linux/skmsg.h>
> #include <linux/perf_event.h>
> @@ -5792,8 +5793,6 @@ struct btf *btf_parse_vmlinux(void)
> /* btf_parse_vmlinux() runs under bpf_verifier_lock */
> bpf_ctx_convert.t = btf_type_by_id(btf, bpf_ctx_convert_btf_id[0]);
>
> - bpf_struct_ops_init(btf, log);
> -
> refcount_set(&btf->refcnt, 1);
>
> err = btf_alloc_id(btf);
> @@ -8621,11 +8620,21 @@ bool btf_type_ids_nocast_alias(struct bpf_verifier_log *log,
> return !strncmp(reg_name, arg_name, cmp_len);
> }
>
> +#ifndef CONFIG_BPF_JIT
> +int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
> + struct btf *btf,
> + struct bpf_verifier_log *log)
> +{
> + return -ENOTSUPP;
> +}
> +#endif /* CONFIG_BPF_JIT */
ah. It is here. This should be in bpf.h.
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