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,URIBL_BLOCKED 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 C194AC2BA1A for ; Mon, 6 Apr 2020 21:21:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 94E6420748 for ; Mon, 6 Apr 2020 21:21:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726370AbgDFVV1 (ORCPT ); Mon, 6 Apr 2020 17:21:27 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:45702 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725895AbgDFVV1 (ORCPT ); Mon, 6 Apr 2020 17:21:27 -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 1jLZBC-00012E-S3; Mon, 06 Apr 2020 23:21:15 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id D5BEC100C47; Mon, 6 Apr 2020 23:21:13 +0200 (CEST) From: Thomas Gleixner To: Benjamin Lamowski , xiaoyao.li@intel.com Cc: philipp.eppelt@kernkonzept.com, bp@alien8.de, fenghua.yu@intel.com, hpa@zytor.com, linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com, nivedita@alum.mit.edu, pbonzini@redhat.com, peterz@infradead.org, sean.j.christopherson@intel.com, tony.luck@intel.com, x86@kernel.org Subject: Re: [PATCH 0/1] x86/split_lock: check split lock feature on initialization In-Reply-To: <20200403174403.306363-1-benjamin.lamowski@kernkonzept.com> References: <20200325030924.132881-1-xiaoyao.li@intel.com> <20200403174403.306363-1-benjamin.lamowski@kernkonzept.com> Date: Mon, 06 Apr 2020 23:21:13 +0200 Message-ID: <87369gl392.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 Benjamin Lamowski writes: > During regression testing of our hypervisor[1] with the current git tip, > we got writes to the TEST_CTRL MSR on hardware that does not support > split lock detection. While the original split_lock implementation does > not exhibit this behavior, the reworked initialization from > dbaba47085b0c unconditionally calls split_lock_verify_msr() from > split_lock_init(). > > After the elaborate checks in cpu_set_core_cap_bits() this seems like an > oversight. The following simple patch fixes our regression by checking > for X86_FEATURE_SPLIT_LOCK_DETECT before accessing the TEST_CTRL MSR. No. It's not an oversight, it's a simplification and it's perfectly legit. rdsmrl_safe() on a unimplemented MSR results in a #GP which is caught and fixed up. Nothing to see here. Thanks, tglx