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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: "Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	"Andrii Nakryiko" <andriin@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Song Liu" <songliubraving@fb.com>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"David Miller" <davem@redhat.com>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>
Subject: Re: [PATCH 12/14] bpf: Add trampolines to kallsyms
Date: Tue, 11 Feb 2020 10:51:27 -0800
Message-ID: <CAEf4BzZFBYVAs5-LowuMov86cbNFdXABkcA=XZAC2JJWg52HKg@mail.gmail.com> (raw)
In-Reply-To: <20200208154209.1797988-13-jolsa@kernel.org>

On Sat, Feb 8, 2020 at 7:43 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding trampolines to kallsyms. It's displayed as
>   bpf_trampoline_<ID> [bpf]
>
> where ID is the BTF id of the trampoline function.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  include/linux/bpf.h     |  2 ++
>  kernel/bpf/trampoline.c | 23 +++++++++++++++++++++++
>  2 files changed, 25 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 7a4626c8e747..b91bac10d3ea 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -502,6 +502,7 @@ struct bpf_trampoline {
>         /* Executable image of trampoline */
>         void *image;
>         u64 selector;
> +       struct bpf_ksym ksym;
>  };
>
>  #define BPF_DISPATCHER_MAX 48 /* Fits in 2048B */
> @@ -573,6 +574,7 @@ struct bpf_image {
>  #define BPF_IMAGE_SIZE (PAGE_SIZE - sizeof(struct bpf_image))
>  bool is_bpf_image_address(unsigned long address);
>  void *bpf_image_alloc(void);
> +void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym);
>  /* Called only from code, so there's no need for stubs. */
>  void bpf_ksym_add(struct bpf_ksym *ksym);
>  void bpf_ksym_del(struct bpf_ksym *ksym);
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 6b264a92064b..1ee29907cbe5 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -96,6 +96,15 @@ bool is_bpf_image_address(unsigned long addr)
>         return ret;
>  }
>
> +void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
> +{
> +       struct bpf_image *image = container_of(data, struct bpf_image, data);
> +
> +       ksym->start = (unsigned long) image;
> +       ksym->end = ksym->start + PAGE_SIZE;

this seems wrong, use BPF_IMAGE_SIZE instead of PAGE_SIZE?

> +       bpf_ksym_add(ksym);
> +}
> +
>  struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
>  {
>         struct bpf_trampoline *tr;
> @@ -131,6 +140,7 @@ struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
>         for (i = 0; i < BPF_TRAMP_MAX; i++)
>                 INIT_HLIST_HEAD(&tr->progs_hlist[i]);
>         tr->image = image;
> +       INIT_LIST_HEAD_RCU(&tr->ksym.lnode);
>  out:
>         mutex_unlock(&trampoline_mutex);
>         return tr;
> @@ -267,6 +277,15 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t)
>         }
>  }
>
> +static void bpf_trampoline_kallsyms_add(struct bpf_trampoline *tr)
> +{
> +       struct bpf_ksym *ksym = &tr->ksym;
> +
> +       snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu",
> +                tr->key & ((u64) (1LU << 32) - 1));

why the 32-bit truncation? also, wouldn't it be more trivial as (u32)tr->key?

> +       bpf_image_ksym_add(tr->image, &tr->ksym);
> +}
> +
>  int bpf_trampoline_link_prog(struct bpf_prog *prog)
>  {
>         enum bpf_tramp_prog_type kind;
> @@ -311,6 +330,8 @@ int bpf_trampoline_link_prog(struct bpf_prog *prog)
>         if (err) {
>                 hlist_del(&prog->aux->tramp_hlist);
>                 tr->progs_cnt[kind]--;
> +       } else if (cnt == 0) {
> +               bpf_trampoline_kallsyms_add(tr);

You didn't handle BPF_TRAMP_REPLACE case above.

Also this if (err) { ... } else if (cnt == 0) { } pattern is a bit
convoluted. How about:

if (err) {
   ... whatever ...
   goto out;
}
if (cnt == 0) { ... }

>         }
>  out:
>         mutex_unlock(&tr->mutex);
> @@ -336,6 +357,8 @@ int bpf_trampoline_unlink_prog(struct bpf_prog *prog)
>         }
>         hlist_del(&prog->aux->tramp_hlist);
>         tr->progs_cnt[kind]--;
> +       if (!(tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT]))
> +               bpf_ksym_del(&tr->ksym);

same, BPF_TRAMP_REPLACE case. I'd also introduce cnt for consistency
with bpf_trampoline_link_prog?

>         err = bpf_trampoline_update(prog->aux->trampoline);
>  out:
>         mutex_unlock(&tr->mutex);
> --
> 2.24.1
>

  reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-08 15:41 [PATCH 00/14] bpf: Add trampoline and dispatcher to /proc/kallsyms Jiri Olsa
2020-02-08 15:41 ` [PATCH 01/14] x86/mm: Rename is_kernel_text to __is_kernel_text Jiri Olsa
2020-02-08 15:41 ` [PATCH 02/14] bpf: Add bpf_trampoline_ name prefix for DECLARE_BPF_DISPATCHER Jiri Olsa
2020-02-08 15:41 ` [PATCH 03/14] bpf: Add struct bpf_ksym Jiri Olsa
2020-02-08 15:41 ` [PATCH 04/14] bpf: Add name to " Jiri Olsa
2020-02-08 15:42 ` [PATCH 05/14] bpf: Add lnode list node " Jiri Olsa
2020-02-08 15:42 ` [PATCH 06/14] bpf: Add bpf_kallsyms_tree tree Jiri Olsa
2020-02-11 18:21   ` Andrii Nakryiko
2020-02-12 10:49     ` Jiri Olsa
2020-02-08 15:42 ` [PATCH 07/14] bpf: Move bpf_tree add/del from bpf_prog_ksym_node_add/del Jiri Olsa
2020-02-08 15:42 ` [PATCH 08/14] bpf: Separate kallsyms add/del functions Jiri Olsa
2020-02-08 15:42 ` [PATCH 09/14] bpf: Add bpf_ksym_add/del functions Jiri Olsa
2020-02-08 15:42 ` [PATCH 10/14] bpf: Re-initialize lnode in bpf_ksym_del Jiri Olsa
2020-02-11 18:28   ` Andrii Nakryiko
2020-02-12 10:43     ` Jiri Olsa
2020-02-08 15:42 ` [PATCH 11/14] bpf: Rename bpf_tree to bpf_progs_tree Jiri Olsa
2020-02-08 15:42 ` [PATCH 12/14] bpf: Add trampolines to kallsyms Jiri Olsa
2020-02-11 18:51   ` Andrii Nakryiko [this message]
2020-02-12 11:10     ` Jiri Olsa
2020-02-12 16:33       ` Andrii Nakryiko
2020-02-12 22:58         ` Jiri Olsa
2020-02-12 23:02         ` Jiri Olsa
2020-02-08 15:42 ` [PATCH 13/14] bpf: Add dispatchers " Jiri Olsa
2020-02-11 19:03   ` Andrii Nakryiko
2020-02-12 10:52     ` Jiri Olsa
2020-02-08 15:42 ` [PATCH 14/14] bpf: Sort bpf kallsyms symbols Jiri Olsa
2020-02-11 19:12   ` Andrii Nakryiko
2020-02-10 15:51 ` [PATCH 00/14] bpf: Add trampoline and dispatcher to /proc/kallsyms Björn Töpel
2020-02-10 16:17   ` Jiri Olsa
2020-02-11 19:32     ` Arnaldo Carvalho de Melo
2020-02-12 11:13       ` Jiri Olsa
2020-02-12 13:31         ` Arnaldo Carvalho de Melo
2020-02-12 22:40           ` Jiri Olsa
2020-02-13 16:23   ` Jiri Olsa
2020-02-11 19:13 ` Arnaldo Carvalho de Melo
2020-02-12 10:46   ` Jiri Olsa

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