在 2022/9/25 9:21, Masami Hiramatsu (Google) 写道:
> On Sat, 24 Sep 2022 09:52:28 +0800
> "liaochang (A)" <liaochang1@xxxxxxxxxx> wrote:
>
>>
>>
>> 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...
>
> Can you update the patch including above as comments in the code?
> Maybe you also have to ensure it on other patches too.
OK，i will add these comments in the code.
Thanks.
>
> Thank you,
>
>>
>> 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@xxxxxxxxxx>
>>>> Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx>
>>>> ---
>>>> 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
>
>
--
BR,
Liao, Chang
