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=-8.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 6B6F9C388F9 for ; Tue, 27 Oct 2020 12:33:55 +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 EA1AC20760 for ; Tue, 27 Oct 2020 12:33:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="myEL6uxO"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="nsIUuBaQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EA1AC20760 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:In-Reply-To:MIME-Version:References: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=4eEaPoCK2pLP0og4X5xX5IC7aUTp3WPJWKD7FdPS6ic=; b=myEL6uxOHIH6HU9fXt2vvi4zd ThXGlT0hmGpq83ojeGsHybmlM6kfj2uH21or6XoZDkJevxi1dOzWZ/AAjfCG4GyxtUeR99h5jXybU anUnjDlWiEwOvz6SRDhAvffy4Kcx1tpuzWx8ZtO9RY9vRENcDXJIzwfQ4V9MSwVxlkNazCBQA+PTH HzF9QBWK8vk5tcMkDxiUOTcNxShws4TkdAGVafSlQDjRvhwGuJLTU2WfFF6QxSoUPr0V9hGVSXA35 9y9IMLyPyhLdIkQs4aPKYwbLW8MSy0hb5llsBcX56bm2haNN9UF7tu3o9uhsiw9f5gqCEHBWFdQnd 55NGM2kYQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXOAH-0003Hj-EE; Tue, 27 Oct 2020 12:33:25 +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 1kXOAF-0003Ge-IH for linux-arm-kernel@lists.infradead.org; Tue, 27 Oct 2020 12:33:24 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 C5FE120760; Tue, 27 Oct 2020 12:33:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603802002; bh=BmWl7MGNJhqhSBKwNlcIBvINOtjP/BOkJRkXZq429MQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nsIUuBaQ6ZmKuMMJsY+y0kSmR5t4EFXnvf579+AkNXIN2+dW5l3gm8HA70j3YCuKX ywVTolAFwgRz0gVJstOoCs8hyc7gmloGLzjNuhxYPT2hpzdo2qvrhiP6PCDtMLEDRy AuF3vNHP5HrUz1ArrEKTBHv/+IV+cBArm6AZncZA= Date: Tue, 27 Oct 2020 12:33:18 +0000 From: Will Deacon To: Jean-Philippe Brucker Subject: Re: [PATCH] arm64: Fix early single-stepping Message-ID: <20201027123317.GA26351@willie-the-truck> References: <20201026172907.1468294-1-jean-philippe@linaro.org> <20201027191318.aba935f7ccf00af9acd89388@kernel.org> <20201027194258.43b157ac0bbccd918fc8756a@kernel.org> <20201027115909.GB1514990@myrica> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201027115909.GB1514990@myrica> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201027_083323_811247_D9031EB8 X-CRM114-Status: GOOD ( 28.37 ) 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: catalin.marinas@arm.com, Masami Hiramatsu , linux-arm-kernel@lists.infradead.org, dianders@chromium.org 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 Tue, Oct 27, 2020 at 12:59:09PM +0100, Jean-Philippe Brucker wrote: > On Tue, Oct 27, 2020 at 07:42:58PM +0900, Masami Hiramatsu wrote: > > On Tue, 27 Oct 2020 19:13:18 +0900 > > Masami Hiramatsu wrote: > > > > > On Mon, 26 Oct 2020 18:29:09 +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. > > > > > > > > Fixes: 36dadef23fcc ("kprobes: Init kprobes in early_initcall") > > > > Signed-off-by: Jean-Philippe Brucker > > > > > > Hi Jean, > > > > > > How have you confirmed this fixes the issue? > > > On my environment, this doesn't fix the issue. > > > > Oops, it was my mistake. I missed to boot up with Xen. (so I find another bug...) > > Anyway this works for me too. > > No worries :) Although now I've been wondering whether it would be better > to just disable the OS lock lazily, on the first call to > enable_debug_monitors(). It might add a tiny performance penalty but would > avoid this problem reappearing if one of the debugger needs to start even > earlier in the future. I'm still uneasy about enabling KDE with the watchpoint registers in an unknown state, so I think this needs more work. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel