lkml.org 
[lkml]   [2022]   [Sep]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] riscv/kprobe: Optimize the performance of patching instruction slot
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>

\
 
 \ /
  Last update: 2022-09-08 00:29    [W:0.083 / U:0.132 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site