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Message-ID: <CAAhV-H55VoFdK8B-PBhYfzHAOQJLnOxLUZGZyHqqdvt=5K3Zhg@mail.gmail.com>
Date: Tue, 5 Aug 2025 12:10:05 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Hengqi Chen <hengqi.chen@...il.com>
Cc: Chenghao Duan <duanchenghao@...inos.cn>, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, yangtiezhu@...ngson.cn, 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,
vincent.mc.li@...il.com, geliang@...nel.org
Subject: Re: [PATCH v5 3/5] LoongArch: BPF: Implement dynamic code
modification support
On Mon, Aug 4, 2025 at 10:02 AM Hengqi Chen <hengqi.chen@...il.com> wrote:
>
> On Wed, Jul 30, 2025 at 9:13 PM Chenghao Duan <duanchenghao@...inos.cn> wrote:
> >
> > This commit adds support for BPF dynamic code modification on the
> > LoongArch architecture.:
> > 1. Implement bpf_arch_text_poke() for runtime instruction patching.
> > 2. Add bpf_arch_text_copy() for instruction block copying.
> > 3. Create bpf_arch_text_invalidate() for code invalidation.
> >
> > 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.
> >
> > larch_insn_text_copy is solely used for BPF. The use of
> > larch_insn_text_copy() requires page_size alignment. Currently, only
> > the size of the trampoline is page-aligned.
> >
> > 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 | 27 ++++++++
> > arch/loongarch/net/bpf_jit.c | 104 ++++++++++++++++++++++++++++++
> > 3 files changed, 132 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..7df63a950 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 +219,32 @@ int larch_insn_patch_text(void *addr, u32 insn)
> > return ret;
> > }
> >
> > +int larch_insn_text_copy(void *dst, void *src, size_t len)
> > +{
> > + int ret;
> > + unsigned long flags;
> > + unsigned long dst_start, dst_end, dst_len;
> > +
> > + dst_start = round_down((unsigned long)dst, PAGE_SIZE);
> > + dst_end = round_up((unsigned long)dst + len, PAGE_SIZE);
> > + dst_len = dst_end - dst_start;
> > +
> > + set_memory_rw(dst_start, dst_len / PAGE_SIZE);
> > + raw_spin_lock_irqsave(&patch_lock, flags);
> > +
> > + ret = copy_to_kernel_nofault(dst, src, len);
> > + if (ret)
> > + pr_err("%s: operation failed\n", __func__);
> > +
> > + raw_spin_unlock_irqrestore(&patch_lock, flags);
> > + set_memory_rox(dst_start, dst_len / 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..5e6ae7e0e 100644
> > --- a/arch/loongarch/net/bpf_jit.c
> > +++ b/arch/loongarch/net/bpf_jit.c
> > @@ -4,8 +4,12 @@
> > *
> > * Copyright (C) 2022 Loongson Technology Corporation Limited
> > */
> > +#include <linux/memory.h>
> > #include "bpf_jit.h"
> >
> > +#define LOONGARCH_LONG_JUMP_NINSNS 5
> > +#define LOONGARCH_LONG_JUMP_NBYTES (LOONGARCH_LONG_JUMP_NINSNS * 4)
> > +
> > #define REG_TCC LOONGARCH_GPR_A6
> > #define TCC_SAVED LOONGARCH_GPR_S5
> >
> > @@ -88,6 +92,7 @@ static u8 tail_call_reg(struct jit_ctx *ctx)
> > */
> > static void build_prologue(struct jit_ctx *ctx)
> > {
> > + int i;
> > int stack_adjust = 0, store_offset, bpf_stack_adjust;
> >
> > bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
> > @@ -98,6 +103,10 @@ static void build_prologue(struct jit_ctx *ctx)
> > stack_adjust = round_up(stack_adjust, 16);
> > stack_adjust += bpf_stack_adjust;
> >
> > + /* Reserve space for the move_imm + jirl instruction */
> > + for (i = 0; i < LOONGARCH_LONG_JUMP_NINSNS; i++)
> > + emit_insn(ctx, nop);
> > +
> > /*
> > * First instruction initializes the tail call count (TCC).
> > * On tail call we skip this instruction, and the TCC is
> > @@ -1367,3 +1376,98 @@ bool bpf_jit_supports_subprog_tailcalls(void)
> > {
> > return true;
> > }
> > +
> > +static int emit_jump_and_link(struct jit_ctx *ctx, u8 rd, u64 target)
> > +{
> > + if (!target) {
> > + pr_err("bpf_jit: jump target address is error\n");
> > + return -EFAULT;
> > + }
> > +
> > + 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);
>
> There should be 5 nops, no ?
Chenghao,
We have already fixed the concurrent problem, now this is the only
issue, please reply tas soon as possible.
Huacai
>
> > + return 0;
> > + }
> > +
> > + return emit_jump_and_link(&ctx, is_call ? LOONGARCH_GPR_T0 : LOONGARCH_GPR_ZERO,
> > + (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[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
> > + u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[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, LOONGARCH_LONG_JUMP_NBYTES))
> > + 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, LOONGARCH_LONG_JUMP_NBYTES))
> > + ret = larch_insn_text_copy(ip, new_insns, LOONGARCH_LONG_JUMP_NBYTES);
> > + mutex_unlock(&text_mutex);
> > + return ret;
> > +}
> > +
> > +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;
> > +
> > + mutex_lock(&text_mutex);
> > + if (larch_insn_text_copy(dst, inst, len))
> > + ret = -EINVAL;
> > + mutex_unlock(&text_mutex);
> > +
> > + kvfree(inst);
> > + return ret;
> > +}
> > +
> > +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> > +{
> > + int ret;
> > +
> > + mutex_lock(&text_mutex);
> > + ret = larch_insn_text_copy(dst, src, len);
> > + mutex_unlock(&text_mutex);
> > + if (ret)
> > + return ERR_PTR(-EINVAL);
> > +
> > + return dst;
> > +}
> > --
>
> bpf_arch_text_invalidate() and bpf_arch_text_copy() is not related to
> BPF trampoline, right ?
>
> > 2.25.1
> >
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