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=-2.0 required=3.0 tests=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 7A505C433DF for ; Fri, 10 Jul 2020 06:36:42 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 429AE206E2 for ; Fri, 10 Jul 2020 06:36:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hvOqj1hD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 429AE206E2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:33682 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jtmeH-0001kq-I6 for qemu-devel@archiver.kernel.org; Fri, 10 Jul 2020 02:36:41 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34730) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jtmcE-0000Kf-OF for qemu-devel@nongnu.org; Fri, 10 Jul 2020 02:34:34 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:47438 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jtmcC-0007sl-Rg for qemu-devel@nongnu.org; Fri, 10 Jul 2020 02:34:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594362871; 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=ZWnDwjLAKtI61PZNG7ENzjs4JhjJ9TzL6LS/QML/gIo=; b=hvOqj1hDbterzgM1KCXEgX41/bY6Vm+iryduG+Q6MYau/M8fPcdt7S+O2P5XuAhuoYtYAy FBiBRjhzbiC+4dvNe04uRMFTBMSC8PTJ1diO0u43zYGy1hSOxelt5EKZbczhRl9uazN9WD 0InmkadF+0Ezihad5tBKRXfdtLrth54= 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-286-pB9d6YXaOYixou8WAoCXZg-1; Fri, 10 Jul 2020 02:34:29 -0400 X-MC-Unique: pB9d6YXaOYixou8WAoCXZg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D8F1C80183C; Fri, 10 Jul 2020 06:34:28 +0000 (UTC) Received: from [10.72.13.228] (ovpn-13-228.pek2.redhat.com [10.72.13.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 952EE5F7D8; Fri, 10 Jul 2020 06:34:13 +0000 (UTC) Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier To: Peter Xu References: <69f6d6e7-a0b1-abae-894e-4e81b7e0cc90@redhat.com> <20200702154540.GI40675@xz-x1> <34fe0e55-c0ae-8e56-462b-6281b6cca4f5@redhat.com> <20200703130338.GD6677@xz-x1> <20200707195429.GF88106@xz-x1> <5004a059-6eb0-4ef3-40b7-94dfbf9ec08f@redhat.com> <20200708141657.GA199122@xz-x1> <14b1ca26-448d-0feb-7529-6546809aaa59@redhat.com> <20200709141037.GF199122@xz-x1> From: Jason Wang Message-ID: Date: Fri, 10 Jul 2020 14:34:11 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200709141037.GF199122@xz-x1> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/09 22:08:55 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Yan Zhao , "Michael S. Tsirkin" , "libvir-list@redhat.com" , Juan Quintela , qemu-devel@nongnu.org, =?UTF-8?Q?Eugenio_P=c3=a9rez?= , Eric Auger , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/7/9 下午10:10, Peter Xu wrote: > On Thu, Jul 09, 2020 at 01:58:33PM +0800, Jason Wang wrote: >>>> - If we care the performance, it's better to implement the MAP event for >>>> vhost, otherwise it could be a lot of IOTLB miss >>> I feel like these are two things. >>> >>> So far what we are talking about is whether vt-d should have knowledge about >>> what kind of events one iommu notifier is interested in. I still think we >>> should keep this as answered in question 1. >>> >>> The other question is whether we want to switch vhost from UNMAP to MAP/UNMAP >>> events even without vDMA, so that vhost can establish the mapping even before >>> IO starts. IMHO it's doable, but only if the guest runs DPDK workloads. When >>> the guest is using dynamic iommu page mappings, I feel like that can be even >>> slower, because then the worst case is for each IO we'll need to vmexit twice: >>> >>> - The first vmexit caused by an invalidation to MAP the page tables, so vhost >>> will setup the page table before IO starts >>> >>> - IO/DMA triggers and completes >>> >>> - The second vmexit caused by another invalidation to UNMAP the page tables >>> >>> So it seems to be worse than when vhost only uses UNMAP like right now. At >>> least we only have one vmexit (when UNMAP). We'll have a vhost translate() >>> request from kernel to userspace, but IMHO that's cheaper than the vmexit. >> >> Right but then I would still prefer to have another notifier. >> >> Since vtd_page_walk has nothing to do with device IOTLB. IOMMU have a >> dedicated command for flushing device IOTLB. But the check for >> vtd_as_has_map_notifier is used to skip the device which can do demand >> paging via ATS or device specific way. If we have two different notifiers, >> vhost will be on the device iotlb notifier so we don't need it at all? > But we can still have iommu notifier that only registers to UNMAP even after we > introduce dev-iotlb notifier? We don't want to do page walk for them as well. > TCG should be the only one so far, but I don't know.. maybe there can still be > new ones? I think you're right. But looking at the codes, it looks like the check of vtd_as_has_map_notifier() was only used in: 1) vtd_iommu_replay() 2) vtd_iotlb_page_invalidate_notify() (PSI) For the replay, it's expensive anyhow. For PSI, I think it's just about one or few mappings, not sure it will have obvious performance impact. And I had two questions: 1) The codes doesn't check map for DSI or GI, does this match what spec said? (It looks to me the spec is unclear in this part) 2) for the replay() I don't see other implementations (either spapr or generic one) that did unmap (actually they skip unmap explicitly), any reason for doing this in intel IOMMU? Thanks > > Thanks, >