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=-8.1 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=ham 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 F12B7C433DB for ; Mon, 8 Feb 2021 23:31:24 +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 59C7364E25 for ; Mon, 8 Feb 2021 23:31:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 59C7364E25 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]:51862 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9G03-0001Md-6X for qemu-devel@archiver.kernel.org; Mon, 08 Feb 2021 18:31:23 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:49460) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9D4l-0002VT-IL for qemu-devel@nongnu.org; Mon, 08 Feb 2021 15:24:03 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:60979) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9D4j-0005Hl-PV for qemu-devel@nongnu.org; Mon, 08 Feb 2021 15:24:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612815840; 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=5Cf21BGBBt+q5kxEhbwFomUHiOyb9jaMRZTQNWGYc40=; b=Cgzj+QOlrpXRTcHFxs/CuPDbpJzCjKov7VORKUiCTDygJNcYBt4jh9b+e/RzENf89+uOn8 tHhjscWNfQIOERLNN3C57tAkrUPf0JZV3N7sJMoiRe8cxWcnyqhwEqIgqWL6HivXb11oGN C9+BNaQhMmDpoDHrXNBuKvrwtC7EYc8= 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-489-_bcfSqhPNSSXbmBdh-p5QA-1; Mon, 08 Feb 2021 15:23:59 -0500 X-MC-Unique: _bcfSqhPNSSXbmBdh-p5QA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 11339107ACF4; Mon, 8 Feb 2021 20:23:58 +0000 (UTC) Received: from [10.36.112.10] (ovpn-112-10.ams2.redhat.com [10.36.112.10]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5BDEE1346F; Mon, 8 Feb 2021 20:23:50 +0000 (UTC) Subject: Re: [PATCH] vhost: Unbreak SMMU and virtio-iommu on dev-iotlb support To: Peter Xu , "Tian, Kevin" References: <20210204191228.187550-1-peterx@redhat.com> <2382a93d-41c1-24fd-144f-87ee18171bc9@redhat.com> <213acf9a-d1c0-3a1d-4846-877d90fadc03@redhat.com> <20210205153107.GX6468@xz-x1> <20210207144715.GG3195@xz-x1> From: Auger Eric Message-ID: <40575583-6f3f-7985-dfcf-a557d671cfc9@redhat.com> Date: Mon, 8 Feb 2021 21:23:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210207144715.GG3195@xz-x1> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eric.auger@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.57, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.265, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Jean-Philippe Brucker , Eugenio Perez Martin , Jason Wang , "qemu-devel@nongnu.org" , "Michael S . Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi, On 2/7/21 3:47 PM, Peter Xu wrote: > Hi, Kevin, > > On Sun, Feb 07, 2021 at 09:04:55AM +0000, Tian, Kevin wrote: >>> From: Peter Xu >>> Sent: Friday, February 5, 2021 11:31 PM >>> >>>>> >>>>> >>>>>> or virtio-iommu >>>>>> since dev-iotlb (or PCIe ATS) >>>>> >>>>> >>>>> We may need to add this in the future. >>>> added Jean-Philippe in CC >>> >>> So that's the part I'm unsure about.. Since everybody is cced so maybe good >>> time to ask. :) >>> >>> The thing is I'm still not clear on whether dev-iotlb is useful for a full >>> emulation environment and how that should differ from a normal iotlb, since >>> after all normal iotlb will be attached with device information too. >> >> dev-iotlb is useful in two manners.First, it's a functional prerequisite for >> supporting I/O page faults. If I understand correctly, the stall model of the ARM SMMU allows IOPF I guess without dev-iotlb (ATS). However indeed PRI requires ATS. > > Is this also a hard requirement for virtio-iommu, which is not a real hardware > after all? > >> Second, it has performance benefit as you don't >> need to contend the lock of global iotlb. > > Hmm.. are you talking about e.g. vt-d driver or virtio-iommu? > > Assuming it's about vt-d, qi_flush_dev_iotlb() will still call qi_submit_sync() > and taking the same global QI lock, as I see it, or I could be wrong somewhere. > I don't see where dev-iotlb has a standalone channel for delivery. > > For virtio-iommu, we haven't defined dev-iotlb, right? no there is no such feature at the moment. If my understanding is correct this would only make sense when protecting a HW device. In that case the underlying physical IOMMU would be programmed for ATS. When protecting a virtio device (inc. vhost) what would be the adventage over the current standard unmap notifier? Thanks Eric Sorry I missed things > when I completely didn't follow virtio-iommu recently - let's say if > virtio-iommu in the future can support per-dev dev-iotlb queue so it doesn't > need a global lock, what if we make it still per-device but still delivering > iotlb message? Again, it's still a bit unclear to me why a full emulation > iommu would need that definition of "iotlb" and "dev-iotlb". > >> >>> >>> For real hardwares, they make sense because they ask for two things: iotlb is >>> for IOMMU, but dev-iotlb is for the device cache. For emulation >>> environment >>> (virtio-iommu is the case) do we really need that complexity? >>> >>> Note that even if there're assigned devices under virtio-iommu in the future, >>> we can still isolate that and iiuc we can easily convert an iotlb (from >>> virtio-iommu) into a hardware IOMMU dev-iotlb no matter what type of >>> IOMMU is >>> underneath the vIOMMU. >>> >> >> Didn't get this point. Hardware dev-iotlb is updated by hardware (between >> the device and the IOMMU). How could software convert a virtual iotlb >> entry into hardware dev-iotlb? > > I mean if virtio-iommu must be run in a guest, then we can trap that message > first, right? If there're assigned device in the guest, we must convert that > invalidation to whatever message required for the host, that seems to not > require the virtio-iommu to have dev-iotlb knowledge, still? > > Thanks, >