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 6A6DEC43331 for ; Tue, 24 Mar 2020 13:31:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 42CEA20775 for ; Tue, 24 Mar 2020 13:31:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728834AbgCXNbt (ORCPT ); Tue, 24 Mar 2020 09:31:49 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:44907 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727686AbgCXNbr (ORCPT ); Tue, 24 Mar 2020 09:31:47 -0400 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 1jGjeT-00059H-NX; Tue, 24 Mar 2020 14:31:29 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 68700100292; Tue, 24 Mar 2020 14:31:28 +0100 (CET) From: Thomas Gleixner To: Xiaoyao Li , Ingo Molnar , Borislav Petkov , hpa@zytor.com, Paolo Bonzini , Sean Christopherson , kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Andy Lutomirski , Peter Zijlstra , Arvind Sankar , Fenghua Yu , Tony Luck , Vitaly Kuznetsov , Jim Mattson Subject: Re: [PATCH v5 1/9] x86/split_lock: Rework the initialization flow of split lock detection In-Reply-To: <95093fb0-df88-0543-c7eb-32b94ac4f99e@intel.com> References: <20200315050517.127446-1-xiaoyao.li@intel.com> <20200315050517.127446-2-xiaoyao.li@intel.com> <87zhc7ovhj.fsf@nanos.tec.linutronix.de> <95093fb0-df88-0543-c7eb-32b94ac4f99e@intel.com> Date: Tue, 24 Mar 2020 14:31:28 +0100 Message-ID: <87imitev67.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 Xiaoyao Li writes: > On 3/24/2020 1:02 AM, Thomas Gleixner wrote: >> Xiaoyao Li writes: >> >>> Current initialization flow of split lock detection has following issues: >>> 1. It assumes the initial value of MSR_TEST_CTRL.SPLIT_LOCK_DETECT to be >>> zero. However, it's possible that BIOS/firmware has set it. >> >> Ok. >> >>> 2. X86_FEATURE_SPLIT_LOCK_DETECT flag is unconditionally set even if >>> there is a virtualization flaw that FMS indicates the existence while >>> it's actually not supported. >>> >>> 3. Because of #2, KVM cannot rely on X86_FEATURE_SPLIT_LOCK_DETECT flag >>> to check verify if feature does exist, so cannot expose it to >>> guest. >> >> Sorry this does not make anny sense. KVM is the hypervisor, so it better >> can rely on the detect flag. Unless you talk about nested virt and a >> broken L1 hypervisor. >> > > Yeah. It is for the nested virt on a broken L1 hypervisor. Then please spell it out in the changelog. Changelogs which need crystalballs to decode are pretty useless. Thanks, tglx