[PATCH] riscv/kprobe: Optimize the performance of patching instruction slot
liaochang (A)
liaochang1 at huawei.com
Wed Sep 7 18:43:45 PDT 2022
Thanks for comment.
在 2022/9/8 1:21, Jisheng Zhang 写道:
> 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.
>
It is indeed necessary to stop machine when arm kprobe under SMP,
but i don't think it need to stop machine when prepare instruction slot,
two reasons:
1. Instruction slot is dynamically allocated data.
2. Kernel would not execute instruction slot until original instruction
is replaced by breakpoint.
>>
>> Signed-off-by: Liao Chang <liaochang1 at huawei.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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> .
--
BR,
Liao, Chang
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