Re: [PATCH bpf-next 2/5] bpf: factor out a helper to prepare trampoline for struct_ops prog

From: Martin KaFai Lau <kafai@fb.com>
To: Hou Tao <houtao1@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, <netdev@vger.kernel.org>,
	<bpf@vger.kernel.org>
Subject: Re: [PATCH bpf-next 2/5] bpf: factor out a helper to prepare trampoline for struct_ops prog
Date: Wed, 29 Sep 2021 10:56:20 -0700	[thread overview]
Message-ID: <20210929175620.yi4jfpllhugys6eo@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210928025228.88673-3-houtao1@huawei.com>

On Tue, Sep 28, 2021 at 10:52:25AM +0800, Hou Tao wrote:
> Factor out a helper bpf_prepare_st_ops_prog() to prepare trampoline
> for BPF_PROG_TYPE_STRUCT_OPS prog. It will be used by .test_run
> callback in following patch.
Thanks for the patches.

This preparation change should be the first patch instead.

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 155dfcfb8923..002bbb2c8bc7 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2224,4 +2224,9 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
>  			u32 **bin_buf, u32 num_args);
>  void bpf_bprintf_cleanup(void);
>  
> +int bpf_prepare_st_ops_prog(struct bpf_tramp_progs *tprogs,
> +			    struct bpf_prog *prog,
> +			    const struct btf_func_model *model,
> +			    void *image, void *image_end);
Move it under where other bpf_struct_ops_.*() resides in bpf.h.

> +
>  #endif /* _LINUX_BPF_H */
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 9abcc33f02cf..ec3c25174923 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -312,6 +312,20 @@ static int check_zero_holes(const struct btf_type *t, void *data)
>  	return 0;
>  }
>  
> +int bpf_prepare_st_ops_prog(struct bpf_tramp_progs *tprogs,
> +			    struct bpf_prog *prog,
> +			    const struct btf_func_model *model,
> +			    void *image, void *image_end)
The existing struct_ops functions in the kernel now have naming like
bpf_struct_ops_.*().  How about renaming it to
bpf_struct_ops_prepare_trampoline()?

> +{
> +	u32 flags;
> +
> +	tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
> +	tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
> +	flags = model->ret_size > 0 ? BPF_TRAMP_F_RET_FENTRY_RET : 0;
> +	return arch_prepare_bpf_trampoline(NULL, image, image_end,
> +					   model, flags, tprogs, NULL);
> +}
> +
>  static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>  					  void *value, u64 flags)
>  {
> @@ -368,7 +382,6 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>  		const struct btf_type *mtype, *ptype;
>  		struct bpf_prog *prog;
>  		u32 moff;
> -		u32 flags;
>  
>  		moff = btf_member_bit_offset(t, member) / 8;
>  		ptype = btf_type_resolve_ptr(btf_vmlinux, member->type, NULL);
> @@ -430,14 +443,9 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>  			goto reset_unlock;
>  		}
>  
> -		tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
> -		tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
> -		flags = st_ops->func_models[i].ret_size > 0 ?
> -			BPF_TRAMP_F_RET_FENTRY_RET : 0;
This change can't apply to bpf-next now because
commit 356ed64991c6 ("bpf: Handle return value of BPF_PROG_TYPE_STRUCT_OPS prog")
is not pulled into bpf-next yet.  Please mention the dependency
in the cover letter if it is still the case in v2.

> -		err = arch_prepare_bpf_trampoline(NULL, image,
> -						  st_map->image + PAGE_SIZE,
> -						  &st_ops->func_models[i],
> -						  flags, tprogs, NULL);
> +		err = bpf_prepare_st_ops_prog(tprogs, prog,
> +					      &st_ops->func_models[i],
> +					      image, st_map->image + PAGE_SIZE);
>  		if (err < 0)
>  			goto reset_unlock;
>  
> -- 
> 2.29.2
> 