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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 1565EC54E49 for ; Sun, 10 May 2020 10:15:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE466206A3 for ; Sun, 10 May 2020 10:15:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728929AbgEJKPu (ORCPT ); Sun, 10 May 2020 06:15:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1725839AbgEJKPt (ORCPT ); Sun, 10 May 2020 06:15:49 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BB5EC061A0C for ; Sun, 10 May 2020 03:15:49 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jXizf-0004wH-LN; Sun, 10 May 2020 12:15:35 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 987FC100D21; Sun, 10 May 2020 12:15:34 +0200 (CEST) From: Thomas Gleixner To: Vegard Nossum Cc: tony.luck@intel.com, ak@linux.intel.com, chang.seok.bae@intel.com, x86@kernel.org, Sasha Levin , linux-kernel@vger.kernel.org, luto@kernel.org Subject: Re: [PATCH v10 00/18] Enable FSGSBASE instructions In-Reply-To: References: <20200423232207.5797-1-sashal@kernel.org> <5a6a0ef5-4dfc-d0b1-9181-5df4211cfcd9@oracle.com> Date: Sun, 10 May 2020 12:15:34 +0200 Message-ID: <87h7wo3xkp.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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, tglx