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Message-ID: <20250717092746.GA993901@chenghao-pc>
Date: Thu, 17 Jul 2025 17:27:46 +0800
From: Chenghao Duan <duanchenghao@...inos.cn>
To: Hengqi Chen <hengqi.chen@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
yangtiezhu@...ngson.cn, 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 Wed, Jul 16, 2025 at 08:21:59PM +0800, Hengqi Chen wrote:
> On Wed, Jul 9, 2025 at 1:50 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;
> > + }
>
> Again, why do you do copy_to_kernel_nofault() in a loop ?
The while loop processes all sizes. I referred to how ARM64 and
RISC-V64 handle this using loops as well.
> This larch_insn_text_copy() can be part of the first patch like
> larch_insn_gen_{beq,bne}. WDYT ?
>From my perspective, it is acceptable to include both
larch_insn_text_copy and larch_insn_gen_{beq,bne} in the same patch,
or place them in the bpf_arch_xxxx patch. larch_insn_text_copy is
solely used for BPF; the application scope of larch_insn_gen_{beq,bne}
is not limited to BPF.
>
> > + 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;
> > +}
> > +
> > +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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