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 B41A6C43143 for ; Thu, 21 Jun 2018 23:05:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5C1CB22520 for ; Thu, 21 Jun 2018 23:05:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5C1CB22520 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 S933935AbeFUXFc (ORCPT ); Thu, 21 Jun 2018 19:05:32 -0400 Received: from mga14.intel.com ([192.55.52.115]:31739 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933446AbeFUXFb (ORCPT ); Thu, 21 Jun 2018 19:05:31 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jun 2018 16:05:30 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,253,1526367600"; d="scan'208";a="59940484" Received: from romley-ivt3.sc.intel.com ([172.25.110.60]) by fmsmga002.fm.intel.com with ESMTP; 21 Jun 2018 16:05:30 -0700 Date: Thu, 21 Jun 2018 16:05:02 -0700 From: Fenghua Yu To: Peter Zijlstra Cc: Fenghua Yu , Thomas Gleixner , 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 00/16] x86/split_lock: Enable #AC exception for split locked accesses Message-ID: <20180621230501.GC18979@romley-ivt3.sc.intel.com> References: <1527435965-202085-1-git-send-email-fenghua.yu@intel.com> <20180621193738.GA13636@worktop.programming.kicks-ass.net> <20180621201851.GC114883@romley-ivt3.sc.intel.com> <20180621220003.GD114883@romley-ivt3.sc.intel.com> <20180621221006.GC2494@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180621221006.GC2494@hirez.programming.kicks-ass.net> 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 Fri, Jun 22, 2018 at 12:10:06AM +0200, Peter Zijlstra wrote: > On Thu, Jun 21, 2018 at 03:00:03PM -0700, Fenghua Yu wrote: > > The control knob for firmware is to choose continuing firmware execution > > by disabling #AC split lock (default) or stopping firmware execution > > by enabling #AC for split lock. Stopping firmware execution may be useful > > in hard real time system to identify any split lock issue on the platform. > > Having the option only allows broken firmware to continue to exist. > Limiting people in how they can use their machines. But in a real case, when I enable #AC for split lock in kernel, reboot hits #AC because of split lock in firmware code and firmware handles #AC as fatal error and stops continuing to run. It will take long time/forever for firmware to fix the split lock issue. Before the firmware issue is fixed, reboot or S4 cannot run if the feature is enabled by kernel. And if unlucky, I'm afraid the patch set even has no chance to be merged to upstream if maintainer's test machine has firmware split lock issue and the machine simply cannot reboot or go to S4 if the feature is enabled. For those reasons, the current patches just don't trust firmware and disable #AC for split lock for firmware by default and allow sysadmin to enable it for firmware via the control knob. So is it ok to still keep the control knob and disable #AC for split lock for firmware by default? Thanks. -Fenghua