Received: by 2002:a25:e74b:0:0:0:0:0 with SMTP id e72csp2008921ybh; Tue, 14 Jul 2020 13:02:59 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwCckH8Jnnv3nUR41yIkHt6HzFJOkwiUg0OqF8Zt2usZaC1PJNPS2ZxpDVSTkiVKapuRIHx X-Received: by 2002:a17:906:7283:: with SMTP id b3mr6328369ejl.163.1594756979032; Tue, 14 Jul 2020 13:02:59 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1594756979; cv=none; d=google.com; s=arc-20160816; b=i0C93RsyOxrz9IQNy3CJis8B3auiRbEXzotp4t44vuAJYuk9YvJlsgBVPrkuu1Q5j7 gEW9kFj1F8sQTs2s9KGaNToJb9fd/vHSEX6UFj5LUNayFwNKqkMyaeoNMRSz7j67iELD eTSLKfmUIWDhnDpXCTc7oknqu3E5rUeqnuV+V/TzsUFOU5p2KbxMi+dpCWqTK6eaOSEf aOrKXK71lMdgju6qRzGni/tREOLA0BOUTCqf4pTY99gl/KJV492ZRZiW9BDvVYCpDNW8 02LZy9UiUwWZeHswGN7lpCKP20L/pCnnA/AsQ2l/foCXCRtzzQ82sWxbWACanGfTKyR/ o/kQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:user-agent:in-reply-to :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:ironport-sdr:ironport-sdr; bh=+uMLeVPvtYQR+zNp3P5lgfmKP+0u0jwpAAwpOUqjd+4=; b=JiTNcY9mPYAtbKUPsw5MXdndv2ZWtZFRE7MjUz90mQmsLYcE3gs5u5qi21Q830P5oh 4W777YxFhgrYOc/tTmpJS9RMzdwtyfgfHz+utqT7QCYxkI6B+XyS6B/3TCN7tsB6J10E HUfdnaQjdcqc4iVVxNx3qstFukBYOMbDtKwlGHjqgNnOi87jHMJbMOvSaIp3ymMhoUgI njyTpFwlkWViKX8F0L0IcIf0qCfX3uE0Lw5WKmS7F/H+yG8K3hL1+o7/dRLpGiqQFF1d GBhb7/6msxPd+AAuzEoCpsdzHipAjKg21j3uAwW0ytRHVAS2BlgK+IJ4G15pw+FB+ZM2 +fSQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id la26si10759235ejb.587.2020.07.14.13.02.34; Tue, 14 Jul 2020 13:02:59 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729556AbgGNUAm (ORCPT + 99 others); Tue, 14 Jul 2020 16:00:42 -0400 Received: from mga06.intel.com ([134.134.136.31]:25480 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726634AbgGNUAl (ORCPT ); Tue, 14 Jul 2020 16:00:41 -0400 IronPort-SDR: 2IhkmdjfPgZ5IuioDDRrcWeaOHjBw3lv0U5MhQaqEp8Xl+psT/JE+D0WyUK0huLJiDBztAorb9 BkNPxqDPHcTg== X-IronPort-AV: E=McAfee;i="6000,8403,9682"; a="210560145" X-IronPort-AV: E=Sophos;i="5.75,352,1589266800"; d="scan'208";a="210560145" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jul 2020 13:00:41 -0700 IronPort-SDR: 4MS2nxEKSwXjwkPrhbmJP1OzdSRAj8lQAiaaHjC1Noo6yhxlz0lTa5uR4dcxyj5kZWZTGL1LmE m/OZlhrKMlvg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,352,1589266800"; d="scan'208";a="299658353" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga002.jf.intel.com with ESMTP; 14 Jul 2020 13:00:40 -0700 Date: Tue, 14 Jul 2020 13:00:40 -0700 From: Ira Weiny To: Dave Hansen Cc: Peter Zijlstra , 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: <20200714200040.GF3008823@iweiny-DESK2.sc.intel.com> 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/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 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, just like the others in the SDM WRMSR > documentation: > > Note that WRMSR to the IA32_TSC_DEADLINE MSR (MSR index 6E0H) > and the X2APIC MSRs (MSR indices 802H to 83FH) are not > serializing. > > This section of the SDM needs to be updated for the PKRS. Also note > that the PKRS WRMSR is similar in its ordering properties to WRPKRU: > > WRPKRU will never execute speculatively. Memory accesses > affected by PKRU register will not execute (even speculatively) > until all prior executions of WRPKRU have completed execution > and updated the PKRU register. > > Which means we don't have to do silliness like LFENCE before WRMSR to > get ordering *back*. This is another tidbit that needs to get added to > the SDM. It should probably also get captured in the changelog. > > But, either way, this *will* make accessing PMEM more expensive from the > kernel. No escaping that. But, we've also got customers saying they > won't deploy PMEM until we mitigate this stray write issue. Those folks > are quite willing to pay the increased in-kernel cost for increased > protection from stray kernel writes. Intel is also quite motivated > because we really like increasing the number of PMEM deployments. :) > > Ira, can you make sure this all gets pulled into the changelogs somewhere? Yes of course. Thanks for writing that up. Ira