linux-kernel - Re: [PATCH v2 2/4] LoongArch: BPF: Add bpf_arch_text

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Message-ID: <CAAhV-H42ofJ_z1Pj4OVwpROzOODqdBMg+ChJ9ULguVkOfLQkkg@mail.gmail.com>
Date: Thu, 19 Jun 2025 23:14:46 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Chenghao Duan <duanchenghao@...inos.cn>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	yangtiezhu@...ngson.cn, hengqi.chen@...il.com, martin.lau@...ux.dev, 
	eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev, 
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me, 
	haoluo@...gle.com, jolsa@...nel.org, kernel@...0n.name, 
	linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev, bpf@...r.kernel.org, 
	guodongtai@...inos.cn, youling.tang@...ux.dev, jianghaoran@...inos.cn
Subject: Re: [PATCH v2 2/4] LoongArch: BPF: Add bpf_arch_text_poke support for Loongarch

Hi, Chenghao,

On Wed, Jun 18, 2025 at 6:51 PM Chenghao Duan <duanchenghao@...inos.cn> wrote:
>
> Implement the bpf_arch_text_poke function for the LoongArch
> architecture. On LoongArch, since symbol addresses in the direct mapping
> region cannot be reached via relative jump instructions from the paged
> mapping region, we use the move_imm+jirl instruction pair as absolute
> jump instructions. These require 2-5 instructions, so we reserve 5 NOP
> instructions in the program as placeholders for function jumps.
I think this patch is a preparation for the 3rd one, then I think
bpf_arch_text_copy and bpf_arch_text_invalidate should also be moved
here because they are the same class as bpf_arch_text_poke.


Huacai

>
> Co-developed-by: George Guo <guodongtai@...inos.cn>
> Signed-off-by: George Guo <guodongtai@...inos.cn>
> Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
> ---
>  arch/loongarch/net/bpf_jit.c | 62 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 62 insertions(+)
>
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index fa1500d4a..24332c596 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -4,6 +4,7 @@
>   *
>   * Copyright (C) 2022 Loongson Technology Corporation Limited
>   */
> +#include <linux/memory.h>
>  #include "bpf_jit.h"
>
>  #define REG_TCC                LOONGARCH_GPR_A6
> @@ -1359,3 +1360,64 @@ bool bpf_jit_supports_subprog_tailcalls(void)
>  {
>         return true;
>  }
> +
> +static int emit_jump_and_link(struct jit_ctx *ctx, u8 rd, u64 ip, u64 target)
> +{
> +       s64 offset = (s64)(target - ip);
> +
> +       if (offset && (offset >= -SZ_128M && offset < SZ_128M)) {
> +               emit_insn(ctx, bl, offset >> 2);
> +       } else {
> +               move_imm(ctx, LOONGARCH_GPR_T1, target, false);
> +               emit_insn(ctx, jirl, rd, LOONGARCH_GPR_T1, 0);
> +       }
> +
> +       return 0;
> +}
> +
> +static int gen_jump_or_nops(void *target, void *ip, u32 *insns, bool is_call)
> +{
> +       struct jit_ctx ctx;
> +
> +       ctx.idx = 0;
> +       ctx.image = (union loongarch_instruction *)insns;
> +
> +       if (!target) {
> +               emit_insn((&ctx), nop);
> +               emit_insn((&ctx), nop);
> +               return 0;
> +       }
> +
> +       return emit_jump_and_link(&ctx, is_call ? LOONGARCH_GPR_T0 : LOONGARCH_GPR_ZERO,
> +                                 (unsigned long)ip, (unsigned long)target);
> +}
> +
> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
> +                      void *old_addr, void *new_addr)
> +{
> +       u32 old_insns[5] = {[0 ... 4] = INSN_NOP};
> +       u32 new_insns[5] = {[0 ... 4] = INSN_NOP};
> +       bool is_call = poke_type == BPF_MOD_CALL;
> +       int ret;
> +
> +       if (!is_kernel_text((unsigned long)ip) &&
> +               !is_bpf_text_address((unsigned long)ip))
> +               return -ENOTSUPP;
> +
> +       ret = gen_jump_or_nops(old_addr, ip, old_insns, is_call);
> +       if (ret)
> +               return ret;
> +
> +       if (memcmp(ip, old_insns, 5 * 4))
> +               return -EFAULT;
> +
> +       ret = gen_jump_or_nops(new_addr, ip, new_insns, is_call);
> +       if (ret)
> +               return ret;
> +
> +       mutex_lock(&text_mutex);
> +       if (memcmp(ip, new_insns, 5 * 4))
> +               ret = larch_insn_text_copy(ip, new_insns, 5 * 4);
> +       mutex_unlock(&text_mutex);
> +       return ret;
> +}
> --
> 2.43.0
>
>