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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 A6CD7C433B4 for ; Thu, 22 Apr 2021 02:05:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74BAD61450 for ; Thu, 22 Apr 2021 02:05:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231538AbhDVCGD (ORCPT ); Wed, 21 Apr 2021 22:06:03 -0400 Received: from mga01.intel.com ([192.55.52.88]:59291 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229706AbhDVCGA (ORCPT ); Wed, 21 Apr 2021 22:06:00 -0400 IronPort-SDR: pEQeo9jEtN38DDsZhqLQ00ww2HSEAkiVFDGRhxJBk9a3/AUqxI7SrsqiOwtpJVl6/mpZOUDN1f OMw0gzMgLdbA== X-IronPort-AV: E=McAfee;i="6200,9189,9961"; a="216470774" X-IronPort-AV: E=Sophos;i="5.82,241,1613462400"; d="scan'208";a="216470774" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Apr 2021 19:05:15 -0700 IronPort-SDR: J7L3j1NCzA4oaG7+eKnjE8m7uBymT3gCZ7SGYKxGkbTyJ8OmUTsIX6+pHmsRhkK/qY6UVDwnEX 9140CvtY6bNw== X-IronPort-AV: E=Sophos;i="5.82,241,1613462400"; d="scan'208";a="391649287" Received: from tassilo.jf.intel.com ([10.54.74.11]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Apr 2021 19:05:14 -0700 Date: Wed, 21 Apr 2021 19:05:12 -0700 From: Andi Kleen To: Jim Mattson Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Kan Liang , linux-kernel@vger.kernel.org, kvm-list@vger.kernel.org, Peter Shier Subject: Re: [PATCH] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[] Message-ID: <20210422020512.GH1401198@tassilo.jf.intel.com> References: <20210422001834.1748319-1-jmattson@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210422001834.1748319-1-jmattson@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 21, 2021 at 05:18:34PM -0700, Jim Mattson wrote: > The only stepping of Broadwell Xeon parts is stepping 1. Fix the > relevant isolation_ucodes[] entry, which previously enumerated > stepping 2. > > Although the original commit was characterized as an optimization, it > is also a workaround for a correctness issue. > > If a PMI arrives between kvm's call to perf_guest_get_msrs() and the > subsequent VM-entry, a stale value for the IA32_PEBS_ENABLE MSR may be > restored at the next VM-exit. This is because, unbeknownst to kvm, PMI > throttling may clear bits in the IA32_PEBS_ENABLE MSR. CPUs with "PEBS > isolation" don't suffer from this issue, because perf_guest_get_msrs() > doesn't report the IA32_PEBS_ENABLE value. Acked-by: Andi Kleen -Andi