Messages in this thread | | | Date | Thu, 8 Sep 2022 09:43:45 +0800 | Subject | Re: [PATCH] riscv/kprobe: Optimize the performance of patching instruction slot | From | "liaochang (A)" <> |
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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@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 >> >> >> _______________________________________________ >> linux-riscv mailing list >> linux-riscv@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-riscv > .
-- BR, Liao, Chang
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