linux-kernel - Re: [PATCH V2 3/3] arm64/kprobe: Optimize the performance of patching single-step slot

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Date:   Fri, 23 Sep 2022 09:24:55 +0800
From:   "liaochang (A)" <liaochang1@...wei.com>
To:     Will Deacon <will@...nel.org>
CC:     <catalin.marinas@....com>, <guoren@...nel.org>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <rostedt@...dmis.org>,
        <mhiramat@...nel.org>, <maz@...nel.org>,
        <alexandru.elisei@....com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-csky@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH V2 3/3] arm64/kprobe: Optimize the performance of patching
 single-step slot



在 2022/9/22 21:38, Will Deacon 写道:
> On Tue, Sep 13, 2022 at 11:34:54AM +0800, Liao Chang wrote:
>> Single-step slot would not be used until kprobe is enabled, that means
>> no race condition occurs on it under SMP, hence it is safe to pacth ss
>> slot without stopping machine.
>>
>> Signed-off-by: Liao Chang <liaochang1@...wei.com>
>> ---
>>  arch/arm64/kernel/probes/kprobes.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>> index d1d182320245..5902e33fd3b6 100644
>> --- a/arch/arm64/kernel/probes/kprobes.c
>> +++ b/arch/arm64/kernel/probes/kprobes.c
>> @@ -44,11 +44,10 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>>  {
>>  	kprobe_opcode_t *addr = p->ainsn.api.insn;
>> -	void *addrs[] = {addr, addr + 1};
>> -	u32 insns[] = {p->opcode, BRK64_OPCODE_KPROBES_SS};
>>  
>>  	/* prepare insn slot */
>> -	aarch64_insn_patch_text(addrs, insns, 2);
>> +	aarch64_insn_write(addr, p->opcode);
>> +	aarch64_insn_write(addr + 1, BRK64_OPCODE_KPROBES_SS);
>>  
>>  	flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE));
> 
> Hmm, so it looks like prior to your change we were doing the cache
> maintebnance twice: once in aarch64_insn_patch_text() from stop machine
> context and then again in the flush_icache_range() call above.
> 
> I suppose the cleanest thing would be to drop the flush_icache_range()
> call and then use aarch64_insn_patch_text_nosync() instead of
> aarch64_insn_write() in your change.

OK，I will improve it in next version, thanks.

> 
> Will
> .

-- 
BR,
Liao, Chang