linux-kernel - Re: [PATCH v2 5/5] powerpc: kprobes: emulate instructions on kprobe handler re-entry

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Date:   Thu, 13 Apr 2017 13:37:58 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] powerpc: kprobes: emulate instructions on kprobe
 handler re-entry

On Wed, 12 Apr 2017 16:28:28 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:

> On kprobe handler re-entry, try to emulate the instruction rather than
> single stepping always.
> 

> As a related change, remove the duplicate saving of msr as that is
> already done in set_current_kprobe()

If so, this part might be separated as a cleanup patch...

Thanks,

> 
> Acked-by: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/kernel/kprobes.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 8b48f7d046bd..005bd4a75902 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -273,10 +273,17 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
>  			 */
>  			save_previous_kprobe(kcb);
>  			set_current_kprobe(p, regs, kcb);
> -			kcb->kprobe_saved_msr = regs->msr;
>  			kprobes_inc_nmissed_count(p);
>  			prepare_singlestep(p, regs);
>  			kcb->kprobe_status = KPROBE_REENTER;
> +			if (p->ainsn.boostable >= 0) {
> +				ret = try_to_emulate(p, regs);
> +
> +				if (ret > 0) {
> +					restore_previous_kprobe(kcb);
> +					return 1;
> +				}
> +			}
>  			return 1;
>  		} else {
>  			if (*addr != BREAKPOINT_INSTRUCTION) {
> -- 
> 2.12.1
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>