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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 79B28C43144 for ; Sat, 23 Jun 2018 15:05:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E65124C39 for ; Sat, 23 Jun 2018 15:05:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2E65124C39 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751654AbeFWPFz (ORCPT ); Sat, 23 Jun 2018 11:05:55 -0400 Received: from mga02.intel.com ([134.134.136.20]:3700 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751474AbeFWPFx (ORCPT ); Sat, 23 Jun 2018 11:05:53 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Jun 2018 08:05:53 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,262,1526367600"; d="scan'208";a="59605619" Received: from romley-ivt3.sc.intel.com ([172.25.110.60]) by FMSMGA003.fm.intel.com with ESMTP; 23 Jun 2018 08:05:52 -0700 Date: Sat, 23 Jun 2018 08:05:21 -0700 From: Fenghua Yu To: Thomas Gleixner Cc: Fenghua Yu , Ingo Molnar , "H. Peter Anvin" , Ashok Raj , Dave Hansen , Rafael Wysocki , Tony Luck , Alan Cox , Ravi V Shankar , Arjan van de Ven , linux-kernel , x86 Subject: Re: [RFC PATCH 02/16] x86/split_lock: Handle #AC exception for split lock in kernel mode Message-ID: <20180623150521.GG18979@romley-ivt3.sc.intel.com> References: <1527435965-202085-1-git-send-email-fenghua.yu@intel.com> <1527435965-202085-3-git-send-email-fenghua.yu@intel.com> <20180623042033.GF18979@romley-ivt3.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 23, 2018 at 11:17:03AM +0200, Thomas Gleixner wrote: > On Fri, 22 Jun 2018, Fenghua Yu wrote: > > On Fri, Jun 22, 2018 at 12:49:00PM +0200, Thomas Gleixner wrote: > > > On Sun, 27 May 2018, Fenghua Yu wrote: > > > > +static void wait_for_reexecution(void) > > > > +{ > > > > + while (time_before(jiffies, disable_split_lock_jiffies + > > > > + reenable_split_lock_delay)) > > > > + cpu_relax(); > > > > +} > > > > + > > > > +/* > > > > + * TEST_CTL MSR is shared among threads on the same core. To simplify > > > > + * situation, disable_split_lock_jiffies is global instead of per core. > > > > > > This patch surely earns extra points in the trainwreck engineering contest, > > > but that's not taking place on LKML. > > > > > > The whole thing is simply: > > > > > > handle_ac() > > > { > > > if (user_mode(regs)) { > > > do_trap(AC, SIGBUS, ...); > > > } else { > > > disable_ac_on_local_cpu(); > > > WARN_ONCE(1); > > > } > > > } > > > > Should I add kernel parameter or control knob to opt-out the feature? > > A simple command line option 'acoff' or something more sensible should be > ok. No sysfs knobs or whatever please. The Kconfig option is not required > either. Ok. I will have a command line option. BTW, I have a Kconfig option to enable split lock test in kernel mode in patch #15. Are the Kconfig option and the kernel test code still needed in next version? > > > I'm afraid firmware may hang system after handling split lock if the > > feature is enabled by kernel, e.g. "reboot" hits split lock in firmware > > and firmware hangs the system after handling #AC. > > Have you observed the problem in reality? I mean why would 'reboot' be the > critical path? I'd rather expect that EFI callbacks or SMM 'value add' > would trip over it. > > Vs. reboot. If that is the only problem then we might just have to clear > #AC enable before issuing it, but that does not need to be part of the > initial patch set. Its an orthogonal issue. Yes, I do see a real firmware hang after hitting and handling a split lock in firmware during "reboot" in one simulation test environment. Apprantly the split lock (and alignment access) is treated as a failure in firmware. This real case triggered my concern that split lock in any future firmware may happen in any path including run time service, S3/S4/S5, hotplug. If we don't have opt-out option or something similar, system hang from split lock in firmware can be a blocking issue on some platforms. If that happens, bisect always finds the split lock patch to blame. Thanks. -Fenghua