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 X-Spam-Level: X-Spam-Status: No, score=-6.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03BDEC4363A for ; Tue, 27 Oct 2020 00:49:28 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 925CA2076A for ; Tue, 27 Oct 2020 00:49:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="0r8NUPZA"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="1R2xVXlv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 925CA2076A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Mime-Version:References:In-Reply-To:Message-Id: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2ZzQtz3dO3HU0RXAK96EBFqEwUMe118CmTmChWzjEhw=; b=0r8NUPZAV4JKvkIkhwvgoCeoT XkffqVYbfAvjpvraXRPhwdITxEnCRaKlfCFcOCUY7XePwhEL5mRoMJq9akzD/u2hGAx90se9TIekk +nOt4JSUcxpsntAPkmy4/HJg67aCHZmtEoyBCYSsXHqnKfzW/fHatWHU4OzWYreDXbDsOfZM/7gyy FomyYZSRb6FJU3q3t68+GB2hyV1y8Kyo3DTwPdHa2yPocDf1gqTyKzQD8b+9OtQcDaYmun/EPh+Zz 3q9qtXTzzagy8xGH7lBzqerB6UhcTRwEIUh4maFl0WzjBCQW+WmsOCaX6HMzAl0ovsvssc0DbPd1b FGQh+n0EA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXD9p-0006e3-RK; Tue, 27 Oct 2020 00:48:13 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXD9m-0006dS-Rt for linux-arm-kernel@lists.infradead.org; Tue, 27 Oct 2020 00:48:11 +0000 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 613972076A; Tue, 27 Oct 2020 00:48:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603759689; bh=1tOG2+GTb3TrwEoBa5uuFJO/hIUwMKtfi+RWjaTVGTo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=1R2xVXlvX3qwTixSZZqNFHhNJgxEpEUJp9SZCrmra/hsXazsGFuQFuZF9gG422H3c RayEcXa9/67DrUqP6HfhlcCC0b8U7HiIb2HEC8a5lbgTRURyUylr8U2iJzFwkEyfMD YUiC6pqIHl92sQakhExFvSyNvTPJrpQJRdlsl5qg= Date: Tue, 27 Oct 2020 09:48:06 +0900 From: Masami Hiramatsu To: Will Deacon Subject: Re: [PATCH] arm64: Fix early single-stepping Message-Id: <20201027094806.0afe80d0022888964f1cae0b@kernel.org> In-Reply-To: <20201026173837.GB25131@willie-the-truck> References: <20201026172907.1468294-1-jean-philippe@linaro.org> <20201026173837.GB25131@willie-the-truck> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201026_204810_973027_DFBFF305 X-CRM114-Status: GOOD ( 20.52 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jean-Philippe Brucker , mhiramat@kernel.org, dianders@chromium.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 26 Oct 2020 17:38:37 +0000 Will Deacon wrote: > On Mon, Oct 26, 2020 at 06:29:09PM +0100, Jean-Philippe Brucker wrote: > > To use debug features such as single-step, the OS lock must be unlocked > > in the debug registers. Currently this is done in postcore_initcall > > which is now too late. > > > > Commit 36dadef23fcc ("kprobes: Init kprobes in early_initcall") enabled > > using kprobes from early_initcall, when OS lock is still locked. So when > > kprobe attempts to single-step a patched instruction, instead of > > trapping, execution continues until it throws an undef exception: > > > > [ 0.064233] Kprobe smoke test: started > > [ 0.151133] ------------[ cut here ]------------ > > [ 0.151458] kernel BUG at arch/arm64/kernel/traps.c:406! > > [ 0.151812] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP > > ... > > [ 0.162689] Call trace: > > [ 0.163014] do_undefinstr+0x1d4/0x1f4 > > [ 0.163336] el1_sync_handler+0xbc/0x140 > > [ 0.163839] el1_sync+0x80/0x100 > > [ 0.164154] 0xffffffc01001d004 > > [ 0.164527] init_kprobes+0x13c/0x154 > > [ 0.164968] do_one_initcall+0x54/0x2e0 > > [ 0.165322] kernel_init_freeable+0xf4/0x258 > > [ 0.165783] kernel_init+0x20/0x12c > > [ 0.166117] ret_from_fork+0x10/0x30 > > [ 0.166595] Code: 97ffff53 a9425bf5 17ffff9b f9001bf7 (d4210000) > > [ 0.167084] ---[ end trace 36778fdf576e9a79 ]--- > > > > To fix this, unlock the OS lock as early as possible. Do it in > > traps_init() for CPU0, since KGDB wants to use single-step from that > > point on according to commit b322c65f8ca3 ("arm64: Call > > debug_traps_init() from trap_init() to help early kgdb"). > > For secondary CPUs, setup the CPU hotplug handler at early_initcall. Oops, thanks for the fix! I missed it. > Hmm, does this mean we end up setting MDSCR_EL1.KDE before we've reset the > hardware breakpoint/watchpoint registers? Why do we need kprobes so early? This is for boot-time tracing. To enable kprobes events in core_initcall(), we need to enable kprobes itself in early_initcall().(or early_initcall_sync()) With this, we can trace postcore functions with kprobes(it includes some platform initializations), which is making boot-time ftrace more useful. For example, we can trace function-calls in specific code area as I posted an example; https://lore.kernel.org/linux-doc/159887792384.1330989.5993224243767476896.stgit@devnote2/ So this expands the feature to the earlier stages. Thank you, -- Masami Hiramatsu _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel