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Message-ID: <CAK3+h2zbcumLibRXi0Oh5zc1FB6JcQco5CTjTYd8o0DOkijjAw@mail.gmail.com>
Date: Wed, 16 Jul 2025 11:41:24 -0700
From: Vincent Li <vincent.mc.li@...il.com>
To: Chenghao Duan <duanchenghao@...inos.cn>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
yangtiezhu@...ngson.cn, hengqi.chen@...il.com, chenhuacai@...nel.org,
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 v3 4/5] LoongArch: BPF: Add bpf_arch_xxxxx support for Loongarch
On Tue, Jul 8, 2025 at 11:02 PM Chenghao Duan <duanchenghao@...inos.cn> wrote:
>
> Implement the functions of bpf_arch_text_poke, bpf_arch_text_copy, and
> bpf_arch_text_invalidate on 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.
>
> 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/include/asm/inst.h | 1 +
> arch/loongarch/kernel/inst.c | 32 +++++++++++
> arch/loongarch/net/bpf_jit.c | 90 +++++++++++++++++++++++++++++++
> 3 files changed, 123 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index 2ae96a35d..88bb73e46 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -497,6 +497,7 @@ void arch_simulate_insn(union loongarch_instruction insn, struct pt_regs *regs);
> int larch_insn_read(void *addr, u32 *insnp);
> int larch_insn_write(void *addr, u32 insn);
> int larch_insn_patch_text(void *addr, u32 insn);
> +int larch_insn_text_copy(void *dst, void *src, size_t len);
>
> u32 larch_insn_gen_nop(void);
> u32 larch_insn_gen_b(unsigned long pc, unsigned long dest);
> diff --git a/arch/loongarch/kernel/inst.c b/arch/loongarch/kernel/inst.c
> index 674e3b322..8d6594968 100644
> --- a/arch/loongarch/kernel/inst.c
> +++ b/arch/loongarch/kernel/inst.c
> @@ -4,6 +4,7 @@
> */
> #include <linux/sizes.h>
> #include <linux/uaccess.h>
> +#include <linux/set_memory.h>
>
> #include <asm/cacheflush.h>
> #include <asm/inst.h>
> @@ -218,6 +219,37 @@ int larch_insn_patch_text(void *addr, u32 insn)
> return ret;
> }
>
> +int larch_insn_text_copy(void *dst, void *src, size_t len)
> +{
> + unsigned long flags;
> + size_t wlen = 0;
> + size_t size;
> + void *ptr;
> + int ret = 0;
> +
> + set_memory_rw((unsigned long)dst, round_up(len, PAGE_SIZE) / PAGE_SIZE);
> + raw_spin_lock_irqsave(&patch_lock, flags);
> + while (wlen < len) {
> + ptr = dst + wlen;
> + size = min_t(size_t, PAGE_SIZE - offset_in_page(ptr),
> + len - wlen);
> +
> + ret = copy_to_kernel_nofault(ptr, src + wlen, size);
> + if (ret) {
> + pr_err("%s: operation failed\n", __func__);
> + break;
> + }
> + wlen += size;
> + }
> + raw_spin_unlock_irqrestore(&patch_lock, flags);
> + set_memory_rox((unsigned long)dst, round_up(len, PAGE_SIZE) / PAGE_SIZE);
> +
> + if (!ret)
> + flush_icache_range((unsigned long)dst, (unsigned long)dst + len);
> +
> + return ret;
> +}
> +
> u32 larch_insn_gen_nop(void)
> {
> return INSN_NOP;
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 7032f11d3..9cb01f0b0 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
> @@ -1367,3 +1368,92 @@ 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;
> +}
> +
I recommend to add comment for bpf_arch_text_poke() similar to
bpf_arch_text_poke() in arch/arm64/net/bpf_jit_comp.c so we have clear
understanding on how it works, given we already have issue with it
when running xdp-filter from xdp-tools that I reported from another
email thread.
> +int bpf_arch_text_invalidate(void *dst, size_t len)
> +{
> + int i;
> + int ret = 0;
> + u32 *inst;
> +
> + inst = kvmalloc(len, GFP_KERNEL);
> + if (!inst)
> + return -ENOMEM;
> +
> + for (i = 0; i < (len/sizeof(u32)); i++)
> + inst[i] = INSN_BREAK;
> +
> + if (larch_insn_text_copy(dst, inst, len))
> + ret = -EINVAL;
> +
> + kvfree(inst);
> + return ret;
> +}
> +
> +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> +{
> + if (larch_insn_text_copy(dst, src, len))
> + return ERR_PTR(-EINVAL);
> +
> + return dst;
> +}
> --
> 2.43.0
>
>
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