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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 6E6C5C433E5 for ; Mon, 20 Jul 2020 09:16:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CD28206F2 for ; Mon, 20 Jul 2020 09:16:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="hSBeriNH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727106AbgGTJQE (ORCPT ); Mon, 20 Jul 2020 05:16:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726666AbgGTJQE (ORCPT ); Mon, 20 Jul 2020 05:16:04 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 264B3C061794; Mon, 20 Jul 2020 02:16:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=LGLWvg6ZDIUlei0ZDQ3T5GmRjQgNLRaVaWwSYGqHGW4=; b=hSBeriNHtlumBJ+DPG5faJaUBK xOohGFXtfbnZk6s5lws1YyNCXqeSHDgqdGn6Wo7FyyBA8zVImTRfO722gMZD48RZoXPx+JkfpUVlu TKh11UPDMA2/enEZKUwjegXxgRSEG0uJPFvxApi4A1eN+vXlXxim2A/g4A4Ia8LiRgps7RgVk4AUi rGStWRJjZ9iLyu5d8pBo3A2cHvvBEYJbweYyDj0/J3K3u6GyAEp3FGfyjWXdvkuJD8/D+udXHtcZh qpbn6ZAr/RTIgKpXTPWMwjJeHwjDlkVR6Uv9xhWno3N5yy+Bdjf6QTUGXzF98MYmW1Egoo81znxWW dnOw8mjQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxRtr-0005wP-Ts; Mon, 20 Jul 2020 09:15:56 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 89F023010C8; Mon, 20 Jul 2020 11:15:54 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7B365205A7673; Mon, 20 Jul 2020 11:15:54 +0200 (CEST) Date: Mon, 20 Jul 2020 11:15:54 +0200 From: Peter Zijlstra To: Ira Weiny 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: <20200720091554.GN10769@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200717223407.GS3008823@iweiny-DESK2.sc.intel.com> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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 :-)