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,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 54EEFC433E4 for ; Tue, 14 Jul 2020 19:49:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 33B7022B51 for ; Tue, 14 Jul 2020 19:49:46 +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="pR+q0ltz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729442AbgGNTtm (ORCPT ); Tue, 14 Jul 2020 15:49:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48252 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbgGNTtm (ORCPT ); Tue, 14 Jul 2020 15:49:42 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E2ACC061755; Tue, 14 Jul 2020 12:49:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=q7NrJBulspMdgxi2cducPGZ39YVyw0D0jNEe7CHNFek=; b=pR+q0ltz9wN4EMOYLJfOx0i96Z fflfRrIqJ/FjDcRjkjnXWWtoHOwwXb5VsxdrGuZS+CvUr+oUVlTyCv7gRGycAnTBa73nx/ZZzxraY 82iJarBVL45tJXSN9iBukFBmkrK9TjFwkyynR9lgHVj3P/pTN95GAdES3IngOKWCc/IT/AJeExrws B1iS+MFHhiV2wqkcQPS+4cu4PIVmyzJ5wPbo1+MD1rYtVpUtTpPR4NAyL3Qe+F1StOpbl5ZlMwm/d zltUaTYbLueeel/jU/1kBjn+57c1OiyIkuqs9kUC5wGlwJjyFjRHU5uwW598uj7Fo2AqOiGYpCTQs STKoB0Qw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jvQva-0008SY-R4; Tue, 14 Jul 2020 19:49:23 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id CA5909817E0; Tue, 14 Jul 2020 21:49:21 +0200 (CEST) Date: Tue, 14 Jul 2020 21:49:21 +0200 From: Peter Zijlstra To: Dave Hansen Cc: Ira Weiny , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , x86@kernel.org, Dave Hansen , Dan Williams , Vishal Verma , Andrew Morton , Fenghua Yu , 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 12/15] kmap: Add stray write protection for device pages Message-ID: <20200714194921.GJ5523@worktop.programming.kicks-ass.net> References: <20200714070220.3500839-1-ira.weiny@intel.com> <20200714070220.3500839-13-ira.weiny@intel.com> <20200714084451.GQ10769@hirez.programming.kicks-ass.net> <20200714190615.GC3008823@iweiny-DESK2.sc.intel.com> <20200714192930.GH5523@worktop.programming.kicks-ass.net> <50d472d8-e4d9-dd35-f31f-268aa69c76e2@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50d472d8-e4d9-dd35-f31f-268aa69c76e2@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jul 14, 2020 at 12:42:11PM -0700, Dave Hansen wrote: > On 7/14/20 12:29 PM, Peter Zijlstra wrote: > > On Tue, Jul 14, 2020 at 12:06:16PM -0700, Ira Weiny wrote: > >> On Tue, Jul 14, 2020 at 10:44:51AM +0200, Peter Zijlstra wrote: > >>> So, if I followed along correctly, you're proposing to do a WRMSR per > >>> k{,un}map{_atomic}(), sounds like excellent performance all-round :-( > >> Only to pages which have this additional protection, ie not DRAM. > >> > >> User mappings of this memory is not affected (would be covered by User PKeys if > >> desired). User mappings to persistent memory are the primary use case and the > >> performant path. > > Because performance to non-volatile memory doesn't matter? I think Dave > > has a better answer here ... > > So, these WRMSRs are less evil than normal. They're architecturally > non-serializing instructions, Excellent, that should make these a fair bit faster than regular MSRs. > But, either way, this *will* make accessing PMEM more expensive from the > kernel. No escaping that. There's no free lunch, it's just that regular MSRs are fairly horrible.