From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756947AbeAHWJX (ORCPT + 1 other); Mon, 8 Jan 2018 17:09:23 -0500 Received: from mail-sn1nam02on0069.outbound.protection.outlook.com ([104.47.36.69]:41952 "EHLO NAM02-SN1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753022AbeAHWJV (ORCPT ); Mon, 8 Jan 2018 17:09:21 -0500 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Thomas.Lendacky@amd.com; From: Tom Lendacky Subject: [PATCH v2 0/2] x86/cpu/AMD: Make LFENCE a serializing instruction on AMD To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Linus Torvalds , Dan Williams , Dave Hansen , Borislav Petkov , Thomas Gleixner , Tim Chen , Greg Kroah-Hartman , David Woodhouse , Paul Turner Date: Mon, 08 Jan 2018 16:09:12 -0600 Message-ID: <20180108220912.12580.82330.stgit@tlendack-t1.amdoffice.net> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; 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There is less performance impact using LFENCE in this way compared to MFENCE. With LFENCE now being a serializing instruction, it can be also used in rdtsc_ordered() in preference to MFENCE_RDTSC. Since the kernel could be running under a hypervisor that does not allow writing to that MSR, it must be first verified that the write was successful before setting the LFENCE_RDTSC feature. The following patches are included in this series: - Make LFENCE a serializing instruction on AMD - Use LFENCE_RDTSC in preference to MFENCE_RDTSC on AMD This patch series is based on tip:x86/pti. --- Changes from v1: - Add a check verifying the MSR was actually updated - Remove the third patch that eliminates the MFENCE_RDTSC feature (since the feature is still needed) - Adding Dan Williams to the cc since this will impact nospec_barrier(), which will require an alternative_2 to add an MFENCE instruction with an MFENCE_RDTSC check Tom Lendacky (2): x86/cpu/AMD: Make LFENCE a serializing instruction x86/cpu/AMD: Use LFENCE_RDTSC in preference to MFENCE_RDTSC arch/x86/include/asm/msr-index.h | 3 +++ arch/x86/kernel/cpu/amd.c | 27 +++++++++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-) -- Tom Lendacky