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=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 33A63C48BD6 for ; Thu, 27 Jun 2019 12:12:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0FB21208CB for ; Thu, 27 Jun 2019 12:12:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726945AbfF0MMG (ORCPT ); Thu, 27 Jun 2019 08:12:06 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:53483 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726465AbfF0MMF (ORCPT ); Thu, 27 Jun 2019 08:12:05 -0400 Received: from p5b06daab.dip0.t-ipconnect.de ([91.6.218.171] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hgTFg-0001sk-Kg; Thu, 27 Jun 2019 14:11:44 +0200 Date: Thu, 27 Jun 2019 14:11:43 +0200 (CEST) From: Thomas Gleixner To: Xiaoyao Li cc: Fenghua Yu , Ingo Molnar , Borislav Petkov , H Peter Anvin , Peter Zijlstra , Andrew Morton , Dave Hansen , Paolo Bonzini , Radim Krcmar , Christopherson Sean J , Ashok Raj , Tony Luck , Dan Williams , Xiaoyao Li , Sai Praneeth Prakhya , Ravi V Shankar , linux-kernel , x86 , kvm@vger.kernel.org Subject: Re: [PATCH v9 11/17] kvm/vmx: Emulate MSR TEST_CTL In-Reply-To: Message-ID: References: <1560897679-228028-1-git-send-email-fenghua.yu@intel.com> <1560897679-228028-12-git-send-email-fenghua.yu@intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 On Thu, 27 Jun 2019, Xiaoyao Li wrote: > On 6/27/2019 3:12 PM, Thomas Gleixner wrote: > > The real interesting question is whether the #AC on split lock prevents the > > actual bus lock or not. If it does then the above is fine. > > > > If not, then it would be trivial for a malicious guest to set the > > SPLIT_LOCK_ENABLE bit and "handle" the exception pro forma, return to the > > offending instruction and trigger another one. It lowers the rate, but that > > doesn't make it any better. > > > > The SDM is as usual too vague to be useful. Please clarify. > > > This feature is to ensure no bus lock (due to split lock) in hardware, that to > say, when bit 29 of TEST_CTL is set, there is no bus lock due to split lock > can be acquired. So enabling this prevents the bus lock, i.e. the exception is raised before that happens. Please add that information to the changelog as well because that's important to know and makes me much more comfortable handing the #AC back into the guest when it has it enabled. Thanks, tglx