From: "liaochang (A)" <liaochang1@huawei.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: <catalin.marinas@arm.com>, <will@kernel.org>, <guoren@kernel.org>,
<paul.walmsley@sifive.com>, <palmer@dabbelt.com>,
<aou@eecs.berkeley.edu>, <mhiramat@kernel.org>,
<rostedt@goodmis.org>, <maz@kernel.org>,
<alexandru.elisei@arm.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <linux-csky@vger.kernel.org>,
<linux-riscv@lists.infradead.org>
Subject: Re: [PATCH 3/3] arm64/kprobe: Optimize the performance of patching single-step slot
Date: Sat, 24 Sep 2022 09:52:28 +0800 [thread overview]
Message-ID: <19ffdae6-8484-08e5-f408-ab39a97ce5c0@huawei.com> (raw)
In-Reply-To: <Yy2pAEvWKVloVr3U@FVFF77S0Q05N>
在 2022/9/23 20:39, Mark Rutland 写道:
> On Fri, Sep 23, 2022 at 04:46:58PM +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.
>
> I think this is correct, but this depends on a couple of subtleties,
> importantly:
>
> * That the I-cache maintenance for these instructions is complete *before* the
> kprobe BRK is written (and aarch64_insn_patch_text_nosync() ensures this, but
> just omits causing a Context-Synchronization-Event on all CPUS).
So in order to guarantee the I-cache maintenance is observed on all CPUS,
it needs to be followed by a explicit Context-Synchronization-Event, perhaps
it is better to place ISB before kprobe BRK is written.
>
> * That the kprobe BRK results in an exception (and consequently a
> Context-Synchronoization-Event), which ensures that the CPU will fetch the
> single-step slot instructions *after* this, ensuring that the new
> instructions are used.
Yes, because of single-step slot is installed int the BRK execption handler,
so it is not necessary to generate Context-Synchronization-Event via ISB mentioned above...
Thanks.
>
> It would be good if we could call that out explicitly.
>
> Thanks,
> Mark.
>
>> Since I and D caches are coherent within single-step slot from
>> aarch64_insn_patch_text_nosync(), hence no need to do it again via
>> flush_icache_range().
>>
>> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>> Signed-off-by: Liao Chang <liaochang1@huawei.com>
>> ---
>> arch/arm64/kernel/probes/kprobes.c | 7 ++-----
>> 1 file changed, 2 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>> index d1d182320245..29b98bc12833 100644
>> --- a/arch/arm64/kernel/probes/kprobes.c
>> +++ b/arch/arm64/kernel/probes/kprobes.c
>> @@ -44,13 +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);
>> -
>> - flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE));
>> + aarch64_insn_patch_text_nosync(addr, p->opcode);
>> + aarch64_insn_patch_text_nosync(addr + 1, BRK64_OPCODE_KPROBES_SS);
>>
>> /*
>> * Needs restoring of return address after stepping xol.
>> --
>> 2.17.1
>>
>
> .
--
BR,
Liao, Chang
next prev parent reply other threads:[~2022-09-24 1:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-23 8:46 [PATCH V3 0/3] kprobe: Optimize the performance of patching ss Liao Chang
2022-09-23 8:46 ` [PATCH 1/3] riscv/kprobe: Optimize the performance of patching single-step slot Liao Chang
2022-09-23 8:46 ` [PATCH 2/3] csky/kprobe: " Liao Chang
2022-09-23 8:46 ` [PATCH 3/3] arm64/kprobe: " Liao Chang
2022-09-23 12:35 ` Will Deacon
2022-09-23 12:39 ` Mark Rutland
2022-09-24 1:52 ` liaochang (A) [this message]
2022-09-25 1:21 ` Masami Hiramatsu
2022-09-27 1:37 ` liaochang (A)
2022-09-27 2:24 [PATCH V4 0/3] kprobe: Optimize the performance of patching ss Liao Chang
2022-09-27 2:24 ` [PATCH 3/3] arm64/kprobe: Optimize the performance of patching single-step slot Liao Chang
2022-09-29 16:50 ` Catalin Marinas
2022-09-30 1:02 ` liaochang (A)
2022-09-30 8:15 ` Catalin Marinas
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