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@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
