Re: [PATCH bpf-next v5 1/5] bpf, x86: Generate trampolines from bpf_tramp_links

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Apr 12, 2022 at 9:56 AM Kui-Feng Lee <kuifeng@fb.com> wrote:
>
> Replace struct bpf_tramp_progs with struct bpf_tramp_links to collect
> struct bpf_tramp_link(s) for a trampoline.  struct bpf_tramp_link
> extends bpf_link to act as a linked list node.
>
> arch_prepare_bpf_trampoline() accepts a struct bpf_tramp_links to
> collects all bpf_tramp_link(s) that a trampoline should call.
>
> Change BPF trampoline and bpf_struct_ops to pass bpf_tramp_links
> instead of bpf_tramp_progs.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@fb.com>
> ---

Looks good, see two comments below.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  arch/x86/net/bpf_jit_comp.c    | 36 +++++++++--------
>  include/linux/bpf.h            | 38 ++++++++++++------
>  include/linux/bpf_types.h      |  1 +
>  include/uapi/linux/bpf.h       |  1 +
>  kernel/bpf/bpf_struct_ops.c    | 69 ++++++++++++++++++++++----------
>  kernel/bpf/syscall.c           | 23 ++++-------
>  kernel/bpf/trampoline.c        | 73 +++++++++++++++++++---------------
>  net/bpf/bpf_dummy_struct_ops.c | 35 +++++++++++++---
>  tools/bpf/bpftool/link.c       |  1 +
>  tools/include/uapi/linux/bpf.h |  1 +
>  10 files changed, 175 insertions(+), 103 deletions(-)
>

[...]

>  /* Different use cases for BPF trampoline:
> @@ -704,7 +704,7 @@ struct bpf_tramp_progs {
>  struct bpf_tramp_image;
>  int arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *image_end,
>                                 const struct btf_func_model *m, u32 flags,
> -                               struct bpf_tramp_progs *tprogs,
> +                               struct bpf_tramp_links *tlinks,
>                                 void *orig_call);
>  /* these two functions are called from generated trampoline */
>  u64 notrace __bpf_prog_enter(struct bpf_prog *prog);
> @@ -803,9 +803,12 @@ static __always_inline __nocfi unsigned int bpf_dispatcher_nop_func(
>  {
>         return bpf_func(ctx, insnsi);
>  }
> +
> +struct bpf_link;
> +

is this forward declaration still needed? was it supposed to be a
struct bpf_tramp_link instead? and also probably higher above, before
bpf_tramp_links?

>  #ifdef CONFIG_BPF_JIT
> -int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr);
> -int bpf_trampoline_unlink_prog(struct bpf_prog *prog, struct bpf_trampoline *tr);
> +int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
> +int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
>  struct bpf_trampoline *bpf_trampoline_get(u64 key,
>                                           struct bpf_attach_target_info *tgt_info);
>  void bpf_trampoline_put(struct bpf_trampoline *tr);
> @@ -856,12 +859,12 @@ int bpf_jit_charge_modmem(u32 size);
>  void bpf_jit_uncharge_modmem(u32 size);
>  bool bpf_prog_has_trampoline(const struct bpf_prog *prog);
>  #else
> -static inline int bpf_trampoline_link_prog(struct bpf_prog *prog,
> +static inline int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
>                                            struct bpf_trampoline *tr)
>  {
>         return -ENOTSUPP;
>  }
> -static inline int bpf_trampoline_unlink_prog(struct bpf_prog *prog,
> +static inline int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
>                                              struct bpf_trampoline *tr)
>  {
>         return -ENOTSUPP;
> @@ -960,7 +963,6 @@ struct bpf_prog_aux {
>         bool tail_call_reachable;
>         bool xdp_has_frags;
>         bool use_bpf_prog_pack;
> -       struct hlist_node tramp_hlist;
>         /* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
>         const struct btf_type *attach_func_proto;
>         /* function name for valid attach_btf_id */
> @@ -1047,6 +1049,18 @@ struct bpf_link_ops {
>                               struct bpf_link_info *info);
>  };
>
> +struct bpf_tramp_link {
> +       struct bpf_link link;
> +       struct hlist_node tramp_hlist;
> +};
> +
> +struct bpf_tracing_link {
> +       struct bpf_tramp_link link;
> +       enum bpf_attach_type attach_type;
> +       struct bpf_trampoline *trampoline;
> +       struct bpf_prog *tgt_prog;
> +};

struct bpf_tracing_link can stay in syscall.c, no? don't see anyone
needing it outside of syscall.c

> +
>  struct bpf_link_primer {
>         struct bpf_link *link;
>         struct file *file;
> @@ -1084,8 +1098,8 @@ 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,
>                                        void *value);
> -int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_progs *tprogs,
> -                                     struct bpf_prog *prog,
> +int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
> +                                     struct bpf_tramp_link *link,
>                                       const struct btf_func_model *model,
>                                       void *image, void *image_end);

[...]