From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFCCFC07E9D for ; Sat, 24 Sep 2022 01:52:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232991AbiIXBwf (ORCPT ); Fri, 23 Sep 2022 21:52:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232982AbiIXBwc (ORCPT ); Fri, 23 Sep 2022 21:52:32 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0ACFB10196D; Fri, 23 Sep 2022 18:52:32 -0700 (PDT) Received: from kwepemi500012.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4MZBmT4r3qzHqM9; Sat, 24 Sep 2022 09:50:17 +0800 (CST) Received: from [10.67.110.108] (10.67.110.108) by kwepemi500012.china.huawei.com (7.221.188.12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 24 Sep 2022 09:52:29 +0800 Message-ID: <19ffdae6-8484-08e5-f408-ab39a97ce5c0@huawei.com> Date: Sat, 24 Sep 2022 09:52:28 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH 3/3] arm64/kprobe: Optimize the performance of patching single-step slot To: Mark Rutland CC: , , , , , , , , , , , , , References: <20220923084658.99304-1-liaochang1@huawei.com> <20220923084658.99304-4-liaochang1@huawei.com> From: "liaochang (A)" In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.110.108] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemi500012.china.huawei.com (7.221.188.12) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/9/23 20:39, Mark Rutland 写道: > On Fri, Sep 23, 2022 at 04:46:58PM +0800, Liao Chang wrote: >> Single-step slot would not be used until kprobe is enabled, that means >> no race condition occurs on it under SMP, hence it is safe to pacth ss >> slot without stopping machine. > > I think this is correct, but this depends on a couple of subtleties, > importantly: > > * That the I-cache maintenance for these instructions is complete *before* the > kprobe BRK is written (and aarch64_insn_patch_text_nosync() ensures this, but > just omits causing a Context-Synchronization-Event on all CPUS). So in order to guarantee the I-cache maintenance is observed on all CPUS, it needs to be followed by a explicit Context-Synchronization-Event, perhaps it is better to place ISB before kprobe BRK is written. > > * That the kprobe BRK results in an exception (and consequently a > Context-Synchronoization-Event), which ensures that the CPU will fetch the > single-step slot instructions *after* this, ensuring that the new > instructions are used. Yes, because of single-step slot is installed int the BRK execption handler, so it is not necessary to generate Context-Synchronization-Event via ISB mentioned above... Thanks. > > It would be good if we could call that out explicitly. > > Thanks, > Mark. > >> Since I and D caches are coherent within single-step slot from >> aarch64_insn_patch_text_nosync(), hence no need to do it again via >> flush_icache_range(). >> >> Acked-by: Masami Hiramatsu (Google) >> Signed-off-by: Liao Chang >> --- >> arch/arm64/kernel/probes/kprobes.c | 7 ++----- >> 1 file changed, 2 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c >> index d1d182320245..29b98bc12833 100644 >> --- a/arch/arm64/kernel/probes/kprobes.c >> +++ b/arch/arm64/kernel/probes/kprobes.c >> @@ -44,13 +44,10 @@ post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *); >> static void __kprobes arch_prepare_ss_slot(struct kprobe *p) >> { >> kprobe_opcode_t *addr = p->ainsn.api.insn; >> - void *addrs[] = {addr, addr + 1}; >> - u32 insns[] = {p->opcode, BRK64_OPCODE_KPROBES_SS}; >> >> /* prepare insn slot */ >> - aarch64_insn_patch_text(addrs, insns, 2); >> - >> - flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE)); >> + aarch64_insn_patch_text_nosync(addr, p->opcode); >> + aarch64_insn_patch_text_nosync(addr + 1, BRK64_OPCODE_KPROBES_SS); >> >> /* >> * Needs restoring of return address after stepping xol. >> -- >> 2.17.1 >> > > . -- BR, Liao, Chang