From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.2 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 6A11D7D2F0 for ; Fri, 23 Aug 2019 14:57:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726063AbfHWO52 (ORCPT ); Fri, 23 Aug 2019 10:57:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:37758 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726043AbfHWO51 (ORCPT ); Fri, 23 Aug 2019 10:57:27 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3128B22CE3; Fri, 23 Aug 2019 14:57:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566572245; bh=nGyHVGYJBOvLh/YCjAm/19L+X2rQRKDPdrvRJJNSXuY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=yCgfe4zpT8YrkttAdUN3y4hg/Ifyy1eVlbHEVOaPdGHQkit/cwgzI5NfNDg7j0Ba0 KJDFaBx3YCLilzz4JR4n7AK0RXWxoC4x9/U8ywLS0eXKGRjfPj1/9bnQIcSbjzoU9v PNNnSoMRygN5+Sbt/CHba375XEK/XYx1fHjTbgFw= Date: Fri, 23 Aug 2019 23:57:21 +0900 From: Masami Hiramatsu To: Jisheng Zhang Cc: Catalin Marinas , Jonathan Corbet , "Naveen N. Rao" , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Mark Rutland , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Will Deacon Subject: Re: [PATCH v5] arm64: implement KPROBES_ON_FTRACE Message-Id: <20190823235721.fa481fca3475a3afd92c740c@kernel.org> In-Reply-To: <20190822191351.3796aca8@xhacker.debian> References: <20190822191351.3796aca8@xhacker.debian> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Jisheng, On Thu, 22 Aug 2019 11:25:00 +0000 Jisheng Zhang wrote: > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it > eliminates the need for a trap, as well as the need to emulate or > single-step instructions. > > Tested on berlin arm64 platform. > > ~ # mount -t debugfs debugfs /sys/kernel/debug/ > ~ # cd /sys/kernel/debug/ > /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events > > before the patch: > > /sys/kernel/debug # cat kprobes/list > ffffff801009fe28 k _do_fork+0x0 [DISABLED] > > after the patch: > > /sys/kernel/debug # cat kprobes/list > ffffff801009ff54 k _do_fork+0x4 [DISABLED][FTRACE] > > Signed-off-by: Jisheng Zhang Looks good to me. Acked-by: Masami Hiramatsu Thank you, > --- > > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it > eliminates the need for a trap, as well as the need to emulate or > single-step instructions. > > Applied after arm64 FTRACE_WITH_REGS: > http://lists.infradead.org/pipermail/linux-arm-kernel/2019-August/674404.html > > Changes since v4: > - correct reg->pc: probed on foo, then pre_handler see foo+0x4, while > post_handler see foo+0x8 > > Changes since v3: > - move kprobe_lookup_name() and arch_kprobe_on_func_entry to ftrace.c since > we only want to choose the ftrace entry for KPROBES_ON_FTRACE. > - only choose ftrace entry if (addr && !offset) > > Changes since v2: > - remove patch1, make it a single cleanup patch > - remove "This patch" in the change log > - implement arm64's kprobe_lookup_name() and arch_kprobe_on_func_entry instead > of patching the common kprobes code > > Changes since v1: > - make the kprobes/x86: use instruction_pointer and instruction_pointer_set > as patch1 > - add Masami's ACK to patch1 > - add some description about KPROBES_ON_FTRACE and why we need it on > arm64 > - correct the log before the patch > - remove the consolidation patch, make it as TODO > - only adjust kprobe's addr when KPROBE_FLAG_FTRACE is set > - if KPROBES_ON_FTRACE, ftrace_call_adjust() the kprobe's addr before > calling ftrace_location() > - update the kprobes-on-ftrace/arch-support.txt in doc > > .../debug/kprobes-on-ftrace/arch-support.txt | 2 +- > arch/arm64/Kconfig | 1 + > arch/arm64/kernel/probes/Makefile | 1 + > arch/arm64/kernel/probes/ftrace.c | 83 +++++++++++++++++++ > 4 files changed, 86 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/kernel/probes/ftrace.c > > diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > index 68f266944d5f..e8358a38981c 100644 > --- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > +++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > @@ -9,7 +9,7 @@ > | alpha: | TODO | > | arc: | TODO | > | arm: | TODO | > - | arm64: | TODO | > + | arm64: | ok | > | c6x: | TODO | > | csky: | TODO | > | h8300: | TODO | > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 663392d1eae2..928700f15e23 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -167,6 +167,7 @@ config ARM64 > select HAVE_STACKPROTECTOR > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > + select HAVE_KPROBES_ON_FTRACE > select HAVE_KRETPROBES > select HAVE_GENERIC_VDSO > select IOMMU_DMA if IOMMU_SUPPORT > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile > index 8e4be92e25b1..4020cfc66564 100644 > --- a/arch/arm64/kernel/probes/Makefile > +++ b/arch/arm64/kernel/probes/Makefile > @@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \ > simulate-insn.o > obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \ > simulate-insn.o > +obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o > diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c > new file mode 100644 > index 000000000000..9f80905f02fa > --- /dev/null > +++ b/arch/arm64/kernel/probes/ftrace.c > @@ -0,0 +1,83 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +/* > + * Dynamic Ftrace based Kprobes Optimization > + * > + * Copyright (C) Hitachi Ltd., 2012 > + * Copyright (C) 2019 Jisheng Zhang > + * Synaptics Incorporated > + */ > + > +#include > + > +/* Ftrace callback handler for kprobes -- called under preepmt disabed */ > +void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > + struct ftrace_ops *ops, struct pt_regs *regs) > +{ > + struct kprobe *p; > + struct kprobe_ctlblk *kcb; > + > + /* Preempt is disabled by ftrace */ > + p = get_kprobe((kprobe_opcode_t *)ip); > + if (unlikely(!p) || kprobe_disabled(p)) > + return; > + > + kcb = get_kprobe_ctlblk(); > + if (kprobe_running()) { > + kprobes_inc_nmissed_count(p); > + } else { > + unsigned long orig_ip = instruction_pointer(regs); > + > + instruction_pointer_set(regs, ip); > + __this_cpu_write(current_kprobe, p); > + kcb->kprobe_status = KPROBE_HIT_ACTIVE; > + if (!p->pre_handler || !p->pre_handler(p, regs)) { > + /* > + * Emulate singlestep (and also recover regs->pc) > + * as if there is a nop > + */ > + instruction_pointer_set(regs, > + (unsigned long)p->addr + MCOUNT_INSN_SIZE); > + if (unlikely(p->post_handler)) { > + kcb->kprobe_status = KPROBE_HIT_SSDONE; > + p->post_handler(p, regs, 0); > + } > + instruction_pointer_set(regs, orig_ip); > + } > + /* > + * If pre_handler returns !0, it changes regs->pc. We have to > + * skip emulating post_handler. > + */ > + __this_cpu_write(current_kprobe, NULL); > + } > +} > +NOKPROBE_SYMBOL(kprobe_ftrace_handler); > + > +kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) > +{ > + unsigned long addr = kallsyms_lookup_name(name); > + > + if (addr && !offset) { > + unsigned long faddr; > + /* > + * with -fpatchable-function-entry=2, the first 4 bytes is the > + * LR saver, then the actual call insn. So ftrace location is > + * always on the first 4 bytes offset. > + */ > + faddr = ftrace_location_range(addr, > + addr + AARCH64_INSN_SIZE); > + if (faddr) > + return (kprobe_opcode_t *)faddr; > + } > + return (kprobe_opcode_t *)addr; > +} > + > +bool arch_kprobe_on_func_entry(unsigned long offset) > +{ > + return offset <= AARCH64_INSN_SIZE; > +} > + > +int arch_prepare_kprobe_ftrace(struct kprobe *p) > +{ > + p->ainsn.api.insn = NULL; > + return 0; > +} > -- > 2.23.0.rc1 > -- Masami Hiramatsu