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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 255CFC433E6 for ; Tue, 14 Jul 2020 19:06:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0F4D21D79 for ; Tue, 14 Jul 2020 19:06:06 +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="CJdJ83l0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731187AbgGNTGF (ORCPT ); Tue, 14 Jul 2020 15:06:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41398 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730678AbgGNTGB (ORCPT ); Tue, 14 Jul 2020 15:06:01 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 413CAC061755; Tue, 14 Jul 2020 12:06:01 -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=QtBDCBQMf3lNrZeLLRepSMPPpVKJmWktHMjNgRkoGLQ=; b=CJdJ83l0vKu7yJJ6u6GOgFQPf7 ZyfPiLItdxhC20dtPthP4i8qJ/61lUsTGE18T0J74ZDa4lDh3C0V+jx805qUstzgtOGqTSvCPyddn WiD8e/7NEHoMqk5+9Wv9wAU5wuHUyNnWxW7gGQfxCaFPp7ztMWMiPX4S6/5dRwZ18IWRYJEXMgesv 2MoLYqByx8+66mmpjfL59zNQ9FZdqBCuO37lJzU2woGAMsZOOaA7FaGoTUsGEXhqpdUHvJurxFcYq AIepEEqyyChZWBIhOp0oJfg/WFsjR9f9TKZ8+xmcmRZAGDaYa/3ew+V/GmF86spyiIawHftDfs0Zp Uh+Tti+g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jvQFJ-0000RD-Qw; Tue, 14 Jul 2020 19:05:42 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 44E2B9817E0; Tue, 14 Jul 2020 21:05:39 +0200 (CEST) Date: Tue, 14 Jul 2020 21:05:39 +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: [RFC PATCH 04/15] x86/pks: Preserve the PKRS MSR on context switch Message-ID: <20200714190539.GG5523@worktop.programming.kicks-ass.net> References: <20200714070220.3500839-1-ira.weiny@intel.com> <20200714070220.3500839-5-ira.weiny@intel.com> <20200714082701.GO10769@hirez.programming.kicks-ass.net> <20200714185322.GB3008823@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714185322.GB3008823@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 14, 2020 at 11:53:22AM -0700, Ira Weiny wrote: > On Tue, Jul 14, 2020 at 10:27:01AM +0200, Peter Zijlstra wrote: > > On Tue, Jul 14, 2020 at 12:02:09AM -0700, ira.weiny@intel.com wrote: > > > From: Ira Weiny > > > > > > The PKRS MSR is defined as a per-core register. This isolates memory > > > access by CPU. Unfortunately, the MSR is not preserved by XSAVE. > > > Therefore, We must preserve the protections for individual tasks even if > > > they are context switched out and placed on another cpu later. > > > > This is a contradiction and utter trainwreck. > > I don't understand where there is a contradiction? Perhaps I should have said > the MSR is not XSAVE managed vs 'preserved'? You're stating the MSR is per-*CORE*, and then continue to talk about per-task state. We've had a bunch of MSRs have exactly that problem recently, and it's not fun. We're not going to do that again.