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, URIBL_BLOCKED,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 10F70C433E4 for ; Mon, 20 Jul 2020 18:35:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9EDC2080D for ; Mon, 20 Jul 2020 18:35:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729926AbgGTSfR (ORCPT ); Mon, 20 Jul 2020 14:35:17 -0400 Received: from mga01.intel.com ([192.55.52.88]:45970 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726506AbgGTSfQ (ORCPT ); Mon, 20 Jul 2020 14:35:16 -0400 IronPort-SDR: wrdPvR2QQD5zVs+dlH2xBbA0Vt5zMGyPslee2clS8w7ZNH5VY12LfsWELbf08p7253hzgYUI2B Mrr5waAIgsXQ== X-IronPort-AV: E=McAfee;i="6000,8403,9688"; a="168130225" X-IronPort-AV: E=Sophos;i="5.75,375,1589266800"; d="scan'208";a="168130225" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jul 2020 11:35:16 -0700 IronPort-SDR: wK7wo3tDMannoMaWGv9oSkwguhLqP6DavKpuU2XXsLRCL8yJhaDeTIBrq75zM686eRl+HmbVUR EPP//W3JMNMQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,375,1589266800"; d="scan'208";a="309946010" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by fmsmga004.fm.intel.com with ESMTP; 20 Jul 2020 11:35:16 -0700 Date: Mon, 20 Jul 2020 11:35:16 -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: <20200720183515.GF478573@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> <20200717223407.GS3008823@iweiny-DESK2.sc.intel.com> <20200720091554.GN10769@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200720091554.GN10769@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Jul 20, 2020 at 11:15:54AM +0200, Peter Zijlstra wrote: > On Fri, Jul 17, 2020 at 03:34:07PM -0700, Ira Weiny wrote: > > 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? > > Or get_cpu_ptr(&pkrs_cache), sorry for the typo :-) Ah I see... sorry, yes that will work. Done, Ira