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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 1951DC5ACBF for ; Sun, 15 Mar 2020 05:23:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ECC1B2072A for ; Sun, 15 Mar 2020 05:23:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727310AbgCOFXA (ORCPT ); Sun, 15 Mar 2020 01:23:00 -0400 Received: from mga18.intel.com ([134.134.136.126]:47872 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727235AbgCOFW7 (ORCPT ); Sun, 15 Mar 2020 01:22:59 -0400 IronPort-SDR: SQWZo1R/vkvH1Ng7RlaRrVqmwjTFGCGbiS/4bSvHA6rKVIL5RKwpBvJ2E55OJ6B3oFEpfNwgoY oa0f+bvQDY5A== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Mar 2020 22:22:58 -0700 IronPort-SDR: ql9m47eRovhqBX/qbBbQ9QPhoatA2wWtzcefXyaWIjVMZndBdLUHcjbsxvkL1iIKzi3V2HR/6k 3aWPb5+gpqOw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,555,1574150400"; d="scan'208";a="267194213" Received: from lxy-clx-4s.sh.intel.com ([10.239.43.160]) by fmsmga004.fm.intel.com with ESMTP; 14 Mar 2020 22:22:55 -0700 From: Xiaoyao Li To: Thomas Gleixner , 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 , Xiaoyao Li Subject: [PATCH v5 2/9] x86/split_lock: Avoid runtime reads of the TEST_CTRL MSR Date: Sun, 15 Mar 2020 13:05:10 +0800 Message-Id: <20200315050517.127446-3-xiaoyao.li@intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200315050517.127446-1-xiaoyao.li@intel.com> References: <20200315050517.127446-1-xiaoyao.li@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In a context switch from a task that is detecting split locks to one that is not (or vice versa) we need to update the TEST_CTRL MSR. Currently this is done with the common sequence: read the MSR flip the bit write the MSR in order to avoid changing the value of any reserved bits in the MSR. Cache the value of the TEST_CTRL MSR when we read it during initialization so we can avoid an expensive RDMSR instruction during context switch. Suggested-by: Sean Christopherson Originally-by: Tony Luck Signed-off-by: Xiaoyao Li --- arch/x86/kernel/cpu/intel.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 064ba12defc8..4b3245035b5a 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -1020,6 +1020,14 @@ static void __init split_lock_setup(void) } } +/* + * Soft copy of MSR_TEST_CTRL initialized when we first read the + * MSR. Used at runtime to avoid using rdmsr again just to collect + * the reserved bits in the MSR. We assume reserved bits are the + * same on all CPUs. + */ +static u64 test_ctrl_val; + /* * Locking is not required at the moment because only bit 29 of this * MSR is implemented and locking would not prevent that the operation @@ -1027,16 +1035,14 @@ static void __init split_lock_setup(void) */ static void __sld_msr_set(bool on) { - u64 test_ctrl_val; - - rdmsrl(MSR_TEST_CTRL, test_ctrl_val); + u64 val = test_ctrl_val; if (on) - test_ctrl_val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT; + val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT; else - test_ctrl_val &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT; + val &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT; - wrmsrl(MSR_TEST_CTRL, test_ctrl_val); + wrmsrl(MSR_TEST_CTRL, val); } /* @@ -1048,11 +1054,13 @@ static void __sld_msr_set(bool on) */ static void split_lock_init(struct cpuinfo_x86 *c) { - u64 test_ctrl_val; + u64 val; - if (rdmsrl_safe(MSR_TEST_CTRL, &test_ctrl_val)) + if (rdmsrl_safe(MSR_TEST_CTRL, &val)) goto msr_broken; + test_ctrl_val = val; + switch (sld_state) { case sld_off: if (wrmsrl_safe(MSR_TEST_CTRL, test_ctrl_val & ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT)) -- 2.20.1