Messages in this thread | | | Date | Thu, 8 Sep 2022 07:28:36 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH] riscv/kprobe: Optimize the performance of patching instruction slot |
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On Thu, 8 Sep 2022 01:21:27 +0800 Jisheng Zhang <jszhang@kernel.org> wrote:
> 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.
Yeah, usually the self modifying code needs stop other CPUs some known points so that other CPUs does not execute the instruction which will be modified. Even if a chip ensures that, is that safe for other implementations? (Does RISC-V specification guarantee this behavior?)
Thank you,
> > > > > 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
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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