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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,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 8E343C433B4 for ; Thu, 8 Apr 2021 18:16:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B6E4610CA for ; Thu, 8 Apr 2021 18:16:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232779AbhDHSQm (ORCPT ); Thu, 8 Apr 2021 14:16:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41689 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231676AbhDHSQl (ORCPT ); Thu, 8 Apr 2021 14:16:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617905789; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a+ZAM3G9QEbZhESupLgtt9XPr4Jta/bTYgM9EuA2Thw=; b=F0c5YJiKvEgKZZoboH/bZx9WwMN/8NUIaGx3Lhxnq1D9qK+FdiHHLz2DPhzUThgiqrfjCq 63CchNhZZH/OpPhXK1tiGkOFfOiz5+gDaQY7XUUUoO7CwO+8lFoXib+ZS7WfE0lD7EH4z0 BtKlG/senbKLpz5cBOZS8tnyRB4d2qg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-568-v5LP_p_OOEqJQ2MwT-ujmw-1; Thu, 08 Apr 2021 14:16:27 -0400 X-MC-Unique: v5LP_p_OOEqJQ2MwT-ujmw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DA6E384B9A0; Thu, 8 Apr 2021 18:16:25 +0000 (UTC) Received: from [10.36.113.26] (ovpn-113-26.ams2.redhat.com [10.36.113.26]) by smtp.corp.redhat.com (Postfix) with ESMTP id 542815C1C4; Thu, 8 Apr 2021 18:16:18 +0000 (UTC) Subject: Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature To: Catalin Marinas , Steven Price Cc: Mark Rutland , Peter Maydell , "Dr. David Alan Gilbert" , Andrew Jones , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , James Morse , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry References: <20210330103013.GD18075@arm.com> <8977120b-841d-4882-2472-6e403bc9c797@redhat.com> <20210331092109.GA21921@arm.com> <86a968c8-7a0e-44a4-28c3-bac62c2b7d65@arm.com> <20210331184311.GA10737@arm.com> <20210407151458.GC21451@arm.com> <5e5bf772-1e4d-ca59-a9d8-058a72dfad4f@arm.com> <20210408141853.GA7676@arm.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Thu, 8 Apr 2021 20:16:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210408141853.GA7676@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08.04.21 16:18, Catalin Marinas wrote: > On Wed, Apr 07, 2021 at 04:52:54PM +0100, Steven Price wrote: >> On 07/04/2021 16:14, Catalin Marinas wrote: >>> On Wed, Apr 07, 2021 at 11:20:18AM +0100, Steven Price wrote: >>>> On 31/03/2021 19:43, Catalin Marinas wrote: >>>>> When a slot is added by the VMM, if it asked for MTE in guest (I guess >>>>> that's an opt-in by the VMM, haven't checked the other patches), can we >>>>> reject it if it's is going to be mapped as Normal Cacheable but it is a >>>>> ZONE_DEVICE (i.e. !kvm_is_device_pfn() + one of David's suggestions to >>>>> check for ZONE_DEVICE)? This way we don't need to do more expensive >>>>> checks in set_pte_at(). >>>> >>>> The problem is that KVM allows the VMM to change the memory backing a slot >>>> while the guest is running. This is obviously useful for the likes of >>>> migration, but ultimately means that even if you were to do checks at the >>>> time of slot creation, you would need to repeat the checks at set_pte_at() >>>> time to ensure a mischievous VMM didn't swap the page for a problematic one. >>> >>> Does changing the slot require some KVM API call? Can we intercept it >>> and do the checks there? >> >> As David has already replied - KVM uses MMU notifiers, so there's not really >> a good place to intercept this before the fault. >> >>> Maybe a better alternative for the time being is to add a new >>> kvm_is_zone_device_pfn() and force KVM_PGTABLE_PROT_DEVICE if it returns >>> true _and_ the VMM asked for MTE in guest. We can then only set >>> PG_mte_tagged if !device. >> >> KVM already has a kvm_is_device_pfn(), and yes I agree restricting the MTE >> checks to only !kvm_is_device_pfn() makes sense (I have the fix in my branch >> locally). > > Indeed, you can skip it if kvm_is_device_pfn(). In addition, with MTE, > I'd also mark a pfn as 'device' in user_mem_abort() if > pfn_to_online_page() is NULL as we don't want to map it as Cacheable in > Stage 2. It's unlikely that we'll trip over this path but just in case. > > (can we have a ZONE_DEVICE _online_ pfn or by definition they are > considered offline?) By definition (and implementation) offline. When you get a page = pfn_to_online_page() with page != NULL, that one should never be ZONE_DEVICE (otherwise it would be a BUG). As I said, things are different when exposing dax memory via dax/kmem to the buddy. But then, we are no longer talking about ZONE_DEVICE. -- Thanks, David / dhildenb