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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 278F3C38A2A for ; Sun, 10 May 2020 14:17:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F289020820 for ; Sun, 10 May 2020 14:17:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589120245; bh=NcHP7PMd0HXApatvGbvOymmYm7xrk960gseZ5NaDr94=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=QATPUkZ6jo//BucfxTHl/hu8cjUhT+gPqUfmpM0xBQOGWB8oPnp0qcs6e3dJxX7a5 AVHUWdYJ1+0/drWWAs43WDUZ9un20eBHlNlFXl+a3H9Ya/s6QghTG2UVuyBFmOHnsV vr+l8UAH5g2ufCqWakpwDsA3bhEuokiDQQ4WHyQ4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729103AbgEJORY (ORCPT ); Sun, 10 May 2020 10:17:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:44426 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726085AbgEJORX (ORCPT ); Sun, 10 May 2020 10:17:23 -0400 Received: from localhost (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (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 3C37820731; Sun, 10 May 2020 14:17:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589120243; bh=NcHP7PMd0HXApatvGbvOymmYm7xrk960gseZ5NaDr94=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MU48330oSkeIyrauj9l8jfZAxRCyjJrF8QvJYOIOk7/c121S4+u1LpHxu6K4qDPPX FR+nYCTvtJbuW6lm2ZPG4k1Q5LzJgdj01htjDFE+s/wUxd9whcXKxByDzpyL3sp/wq lG0WFTilwNL9/MXLw3uKpXiU1RxFwsEAKLkAy0sg= Date: Sun, 10 May 2020 10:17:22 -0400 From: Sasha Levin To: Thomas Gleixner Cc: Vegard Nossum , tony.luck@intel.com, ak@linux.intel.com, chang.seok.bae@intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, luto@kernel.org Subject: Re: [PATCH v10 00/18] Enable FSGSBASE instructions Message-ID: <20200510141722.GM13035@sasha-vm> References: <20200423232207.5797-1-sashal@kernel.org> <5a6a0ef5-4dfc-d0b1-9181-5df4211cfcd9@oracle.com> <87h7wo3xkp.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <87h7wo3xkp.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 10, 2020 at 12:15:34PM +0200, Thomas Gleixner wrote: >Vegard Nossum writes: >> On 5/10/20 10:09 AM, Vegard Nossum wrote: >> >> I spoke a few minutes too soon. Just hit this, if anybody wants to have >> a look: >> >> [ 6402.786418] ------------[ cut here ]------------ >> [ 6402.787769] WARNING: CPU: 0 PID: 13802 at arch/x86/kernel/traps.c:811 >> do_debug+0x16c/0x210 > >> [ 6402.820353] Call Trace: >> [ 6402.821043] <#DB> >> [ 6402.821622] debug+0x37/0x70 >> [ 6402.822449] RIP: 0010:arch_stack_walk_user+0x79/0x110 > >That's a cute way to trigger that WARN_ON in the #DB handler. > >> [ 6402.816468] DR0: 0000000000000001 DR1: 0000000040006070 DR2: 00007ffff7ffd000 >> [ 6402.818406] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000003b3062a > >#DB recursion > > [ 6402.832288] RDX: 0000000040006073 > >27: 48 8b 1a mov (%rdx),%rbx > >Breakpoint on user space stack, #DB triggers and the low level ASM >irqflags tracepoint has stacktrace enabled which unwinds into the user >stack and triggers #DB again. > >Bah. I know why I want to ban all that tracing muck from low level entry code. > >> It might not be related to the patch set, mind. > >It's unrelated. Thanks for testing Vegard! -- Thanks, Sasha