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_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 39DA6C43331 for ; Tue, 24 Mar 2020 18:02:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B0AA20719 for ; Tue, 24 Mar 2020 18:02:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727933AbgCXSCR (ORCPT ); Tue, 24 Mar 2020 14:02:17 -0400 Received: from mga06.intel.com ([134.134.136.31]:44915 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727466AbgCXSCQ (ORCPT ); Tue, 24 Mar 2020 14:02:16 -0400 IronPort-SDR: vNku9zUzny8Uuw9u1Zs0fnRB+6BT0NOL1mG8dN/MnV9/pNwkhiQ66QgYUn+nka7Nnbt61e379y rmmc8mr0JgQg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2020 11:02:08 -0700 IronPort-SDR: OYNmRJu447qOcND1nZkGVdZNobHuJ6KpDHrR/c/VCRNJ9Xf1O6/kIyfSfkNhndXoOg3chI0nLn jX3d1rqFGfMw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,301,1580803200"; d="scan'208";a="325988332" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga001.jf.intel.com with ESMTP; 24 Mar 2020 11:02:07 -0700 Date: Tue, 24 Mar 2020 11:02:07 -0700 From: Sean Christopherson To: Thomas Gleixner Cc: Xiaoyao Li , Ingo Molnar , Borislav Petkov , hpa@zytor.com, Paolo Bonzini , kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Peter Zijlstra , Arvind Sankar , Fenghua Yu , Tony Luck , Vitaly Kuznetsov , Jim Mattson Subject: Re: [PATCH v5 3/9] x86/split_lock: Re-define the kernel param option for split_lock_detect Message-ID: <20200324180207.GD5998@linux.intel.com> References: <20200315050517.127446-1-xiaoyao.li@intel.com> <20200315050517.127446-4-xiaoyao.li@intel.com> <87r1xjov3a.fsf@nanos.tec.linutronix.de> <87r1xidoj1.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r1xidoj1.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 24, 2020 at 11:40:18AM +0100, Thomas Gleixner wrote: > Xiaoyao Li writes: > > On 3/24/2020 1:10 AM, Thomas Gleixner wrote: > >> Xiaoyao Li writes: > >> > >>> Change sld_off to sld_disable, which means disabling feature split lock > >>> detection and it cannot be used in kernel nor can kvm expose it guest. > >>> Of course, the X86_FEATURE_SPLIT_LOCK_DETECT is not set. > >>> > >>> Add a new optioin sld_kvm_only, which means kernel turns split lock > >>> detection off, but kvm can expose it to guest. > >> > >> What's the point of this? If the host is not clean, then you better fix > >> the host first before trying to expose it to guests. > > > > It's not about whether or not host is clean. It's for the cases that > > users just don't want it enabled on host, to not break the applications > > or drivers that do have split lock issue. > > It's very much about whether the host is split lock clean. > > If your host kernel is not, then this wants to be fixed first. If your > host application is broken, then either fix it or use "warn". The "kvm only" option was my suggestion. The thought was to provide a way for users to leverage KVM to debug/test kernels without having to have a known good kernel and/or to minimize the risk of crashing their physical system. E.g. debug a misbehaving driver by assigning its associated device to a guest.