linux-kernel - Re: [PATCH] riscv/kprobe: Optimize the performance of patching instruction slot

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Message-ID: <YxjTF2FlIJbbKq0p@xhacker>
Date:   Thu, 8 Sep 2022 01:21:27 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Liao Chang <liaochang1@...wei.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, mhiramat@...nel.org, rostedt@...dmis.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv/kprobe: Optimize the performance of patching
 instruction slot

On Wed, Sep 07, 2022 at 10:33:27AM +0800, Liao Chang wrote:
> Since no race condition occurs on each instruction slot, hence it is
> safe to patch instruction slot without stopping machine.

hmm, IMHO there's race when arming kprobe under SMP, so stopping
machine is necessary here. Maybe I misundertand something.

> 
> Signed-off-by: Liao Chang <liaochang1@...wei.com>
> ---
>  arch/riscv/kernel/probes/kprobes.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> index e6e950b7cf32..eff7d7fab535 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -24,12 +24,14 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>  {
>  	unsigned long offset = GET_INSN_LENGTH(p->opcode);
> +	const kprobe_opcode_t brk_insn = __BUG_INSN_32;
> +	kprobe_opcode_t slot[MAX_INSN_SIZE];
>  
>  	p->ainsn.api.restore = (unsigned long)p->addr + offset;
>  
> -	patch_text(p->ainsn.api.insn, p->opcode);
> -	patch_text((void *)((unsigned long)(p->ainsn.api.insn) + offset),
> -		   __BUG_INSN_32);
> +	memcpy(slot, &p->opcode, offset);
> +	memcpy((void *)((unsigned long)slot + offset), &brk_insn, 4);
> +	patch_text_nosync(p->ainsn.api.insn, slot, offset + 4);
>  }
>  
>  static void __kprobes arch_prepare_simulate(struct kprobe *p)
> -- 
> 2.17.1
> 
> 
> _______________________________________________
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> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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