From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752383AbdBNKH4 (ORCPT ); Tue, 14 Feb 2017 05:07:56 -0500 Received: from smarthost03c.mail.zen.net.uk ([212.23.1.22]:49089 "EHLO smarthost03c.mail.zen.net.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750859AbdBNKHY (ORCPT ); Tue, 14 Feb 2017 05:07:24 -0500 X-Greylist: delayed 332 seconds by postgrey-1.27 at vger.kernel.org; Tue, 14 Feb 2017 05:07:24 EST Message-ID: <1487066837.2978.4.camel@linaro.org> Subject: Re: [BUGFIX PATCH 2/3] kprobes/arm: Skip single-stepping in recursing path if possible From: "Jon Medhurst (Tixy)" To: Masami Hiramatsu , Russell King Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ananth N Mavinakayanahalli , Ingo Molnar , Thomas Gleixner , "H . Peter Anvin" , Wang Nan , Catalin Marinas , Will Deacon , "David A . Long" , Sandeepa Prabhu Date: Tue, 14 Feb 2017 10:07:17 +0000 In-Reply-To: <148699827839.8505.1518065390542643677.stgit@devbox> References: <148699813647.8505.3671818093118978038.stgit@devbox> <148699827839.8505.1518065390542643677.stgit@devbox> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.4-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Originating-smarthost03c-IP: [82.69.122.217] Feedback-ID: 82.69.122.217 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2017-02-14 at 00:04 +0900, Masami Hiramatsu wrote: > Kprobes/arm skips single-stepping (moreover handling the event) > if the conditional instruction must not be executed. This > also apply the rule when we hit the recursing kprobe, so > that kprobe does not count nmissed up in that case. Perhaps that last sentence would read better if written something like: "This also applies that rule when we hit a recursing kprobe, so that the nmissed count isn't incremented in that case." > Signed-off-by: Masami Hiramatsu Acked-by: Jon Medhurst > --- > arch/arm/probes/kprobes/core.c | 19 ++++++++++--------- > 1 file changed, 10 insertions(+), 9 deletions(-) > > diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c > index 264fedb..84989ae 100644 > --- a/arch/arm/probes/kprobes/core.c > +++ b/arch/arm/probes/kprobes/core.c > @@ -265,7 +265,15 @@ void __kprobes kprobe_handler(struct pt_regs *regs) > #endif > > if (p) { > - if (cur) { > + if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) { > + /* > + * Probe hit but conditional execution check failed, > + * so just skip the instruction and continue as if > + * nothing had happened. > + * In this case, we can skip recursing check too. > + */ > + singlestep_skip(p, regs); > + } else if (cur) { > /* Kprobe is pending, so we're recursing. */ > switch (kcb->kprobe_status) { > case KPROBE_HIT_ACTIVE: > @@ -288,7 +296,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs) > /* impossible cases */ > BUG(); > } > - } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) { > + } else { > /* Probe hit and conditional execution check ok. */ > set_current_kprobe(p); > kcb->kprobe_status = KPROBE_HIT_ACTIVE; > @@ -309,13 +317,6 @@ void __kprobes kprobe_handler(struct pt_regs *regs) > } > reset_current_kprobe(); > } > - } else { > - /* > - * Probe hit but conditional execution check failed, > - * so just skip the instruction and continue as if > - * nothing had happened. > - */ > - singlestep_skip(p, regs); > } > } else if (cur) { > /* We probably hit a jprobe. Call its break handler. */ >