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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 D061AC433E1 for ; Fri, 17 Jul 2020 22:34:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B679320691 for ; Fri, 17 Jul 2020 22:34:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726715AbgGQWeJ (ORCPT ); Fri, 17 Jul 2020 18:34:09 -0400 Received: from mga09.intel.com ([134.134.136.24]:49086 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726399AbgGQWeI (ORCPT ); Fri, 17 Jul 2020 18:34:08 -0400 IronPort-SDR: N6PXGVbL9Nm2n2WT61S7xBMhTrgGfpDFQkgzxM/PbjIuza0WdXZzdOFALg9UycVlTls8FvJzNS p+aos1ATWC5Q== X-IronPort-AV: E=McAfee;i="6000,8403,9685"; a="151049456" X-IronPort-AV: E=Sophos;i="5.75,364,1589266800"; d="scan'208";a="151049456" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2020 15:34:08 -0700 IronPort-SDR: kthQsGLObtwSWoOzzNwTRSgtMFbfQX/Q/Mq09Zc/Drf8BGiuQ5/EGHNB8Hy/cRd2302wOqsyVi VatOSgUZMZjQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,364,1589266800"; d="scan'208";a="487118249" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by fmsmga005.fm.intel.com with ESMTP; 17 Jul 2020 15:34:07 -0700 Date: Fri, 17 Jul 2020 15:34:07 -0700 From: Ira Weiny To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Fenghua Yu , x86@kernel.org, Dave Hansen , Dan Williams , Vishal Verma , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch Message-ID: <20200717223407.GS3008823@iweiny-DESK2.sc.intel.com> References: <20200717072056.73134-1-ira.weiny@intel.com> <20200717072056.73134-5-ira.weiny@intel.com> <20200717085954.GY10769@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200717085954.GY10769@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 17, 2020 at 10:59:54AM +0200, Peter Zijlstra wrote: > On Fri, Jul 17, 2020 at 12:20:43AM -0700, ira.weiny@intel.com wrote: > > +/* > > + * Write the PKey Register Supervisor. This must be run with preemption > > + * disabled as it does not guarantee the atomicity of updating the pkrs_cache > > + * and MSR on its own. > > + */ > > +void write_pkrs(u32 pkrs_val) > > +{ > > + this_cpu_write(pkrs_cache, pkrs_val); > > + wrmsrl(MSR_IA32_PKRS, pkrs_val); > > +} > > Should we write that like: > > void write_pkrs(u32 pkr) > { > u32 *pkrs = get_cpu_ptr(pkrs_cache); > if (*pkrs != pkr) { > *pkrs = pkr; > wrmsrl(MSR_IA32_PKRS, pkr); > } > put_cpu_ptrpkrs_cache); > } > > given that we fundamentally need to serialize againt schedule() here. Yes. That seems better. That also means pks_sched_in() can be simplified to just static inline void pks_sched_in(void) { write_pkrs(current->thread.saved_pkrs); } Because of the built WRMSR avoidance. However, pkrs_cache is static so I think I need to use {get,put}_cpu_var() here don't I? Thanks! Ira