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=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 412A3C54FD2 for ; Wed, 25 Mar 2020 03:27:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1FCCE20724 for ; Wed, 25 Mar 2020 03:27:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727360AbgCYD1K (ORCPT ); Tue, 24 Mar 2020 23:27:10 -0400 Received: from mga01.intel.com ([192.55.52.88]:39340 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727253AbgCYD1I (ORCPT ); Tue, 24 Mar 2020 23:27:08 -0400 IronPort-SDR: vKhRNizHQhaRl993yZvAV8tGIzLtohcBjIyivbl1Sl8MGj/vPOjw5c+v4PwNKkA8OazxZ5suVh fzqJnlOMKFpg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2020 20:27:08 -0700 IronPort-SDR: 7I16jIMiWtO8LKycInGLDqLZkstmd2V+72W8N55D6DVRkqRoRYUaMUgMG+8SVfw7uWKIg1uYbF Ci9EJ083pPww== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,302,1580803200"; d="scan'208";a="240290011" Received: from lxy-clx-4s.sh.intel.com ([10.239.43.39]) by fmsmga008.fm.intel.com with ESMTP; 24 Mar 2020 20:27:05 -0700 From: Xiaoyao Li To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , hpa@zytor.com Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Sean Christopherson , Paolo Bonzini , luto@kernel.org, Peter Zijlstra , Arvind Sankar , Fenghua Yu , Tony Luck , Xiaoyao Li Subject: [PATCH v7 2/2] x86/split_lock: Avoid runtime reads of the TEST_CTRL MSR Date: Wed, 25 Mar 2020 11:09:24 +0800 Message-Id: <20200325030924.132881-3-xiaoyao.li@intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200325030924.132881-1-xiaoyao.li@intel.com> References: <20200325030924.132881-1-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 unused and reserved bits of TEST_CTRL MSR with SPLIT_LOCK_DETECT bit cleared 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 | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index deb5c42c2089..1f414578899c 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -45,6 +45,7 @@ enum split_lock_detect_state { * split lock detect, unless there is a command line override. */ static enum split_lock_detect_state sld_state __ro_after_init = sld_off; +static u64 msr_test_ctrl_cache __ro_after_init; /* * Processors which have self-snooping capability can handle conflicting @@ -1037,6 +1038,8 @@ static void __init split_lock_setup(void) break; } + rdmsrl(MSR_TEST_CTRL, msr_test_ctrl_cache); + if (!split_lock_verify_msr(true)) { pr_info("MSR access failed: Disabled\n"); return; @@ -1053,14 +1056,10 @@ static void __init split_lock_setup(void) */ static void sld_update_msr(bool on) { - u64 test_ctrl_val; - - rdmsrl(MSR_TEST_CTRL, test_ctrl_val); + u64 test_ctrl_val = msr_test_ctrl_cache; if (on) test_ctrl_val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT; - else - test_ctrl_val &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT; wrmsrl(MSR_TEST_CTRL, test_ctrl_val); } -- 2.20.1