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Sun, 07 Aug 2022 06:35:13 -0700 (PDT) X-Google-Smtp-Source: AA6agR6b3gJMHnoTNtj37IngASsHIWEjuA+66KHlhEYj9gzwpL5gbhYjiJ9U3VuycAq+eyh6uwiMbA== X-Received: by 2002:a05:600c:35c7:b0:3a3:2612:f823 with SMTP id r7-20020a05600c35c700b003a32612f823mr9706761wmq.33.1659879312980; Sun, 07 Aug 2022 06:35:12 -0700 (PDT) Received: from redhat.com ([2.52.21.123]) by smtp.gmail.com with ESMTPSA id y12-20020adfdf0c000000b0021f138e07acsm8993628wrl.35.2022.08.07.06.35.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Aug 2022 06:35:12 -0700 (PDT) Date: Sun, 7 Aug 2022 09:35:07 -0400 From: "Michael S. Tsirkin" To: Christoph Hellwig Subject: Re: IOTLB support for vhost/vsock breaks crosvm on Android Message-ID: <20220807092733-mutt-send-email-mst@kernel.org> References: <20220805181105.GA29848@willie-the-truck> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: jiyong@google.com, kvm@vger.kernel.org, kernel-team@android.com, Linus Torvalds , keirf@google.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, ascull@google.com, stefanha@redhat.com, maz@kernel.org, Will Deacon X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Sat, Aug 06, 2022 at 11:52:13PM -0700, Christoph Hellwig wrote: > It really is vhost that seems to abuse it so that if the guest > claims it can handle VIRTIO_F_ACCESS_PLATFORM (which every modern > guest should) it enables magic behavior, which I don't think is what > the virtio spec intended. Well the magic behavour happens to be used by QEMU to implement a virtual IOMMU. And when you have a virtual IOMMU you generally want VIRTIO_F_ACCESS_PLATFORM. This is how it came to be reused for that. And since QEMU never passed guest features to vhost unfiltered we never saw the issue even with old QEMU versions on new kernels. It seems natural to pass features unfiltered and we never even said userspace should not do it, so it's quite understandable that this is what corsvm did. -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization 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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23D31C19F2A for ; Sun, 7 Aug 2022 13:35:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233860AbiHGNfT (ORCPT ); Sun, 7 Aug 2022 09:35:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231571AbiHGNfR (ORCPT ); Sun, 7 Aug 2022 09:35:17 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9B11810C1 for ; Sun, 7 Aug 2022 06:35:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659879315; 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: in-reply-to:in-reply-to:references:references; bh=kUQoZ+Z3T3noJLGRnWhyvuGBcgQof1Le7Re/cjImcLw=; b=O3wQz7IEr8AyBH53UrbV+N8ZjvDixx5BvWma5nwK5jFNyc7Mc/+WbYJC/u6g19I1FCDPPu 1EnEv2RqHwnL7sHpkr8VZd50AGh6QIK83NDRu22IxoS77aXwmPGtD37tczYgibRgcTCwOc OIeR7hJ/tKGRSXFZm0XazeaxtRD0f/E= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-247-B09LUSBZPViSCbu4JQ2A7Q-1; Sun, 07 Aug 2022 09:35:14 -0400 X-MC-Unique: B09LUSBZPViSCbu4JQ2A7Q-1 Received: by mail-wm1-f70.google.com with SMTP id 18-20020a05600c029200b003a500b612e2so3560485wmk.9 for ; Sun, 07 Aug 2022 06:35:14 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=kUQoZ+Z3T3noJLGRnWhyvuGBcgQof1Le7Re/cjImcLw=; b=s+bO9gA9wm/BrQySYFkpwkhjTCPgVU7jN+YyIkoGwKMyRLLJzprs6nrnkuiUfQS6AB /oOwNSv2EHI61zg5F1RZEk7FvAyxFCDFZxsDu/HYnUuyVRkhCQUL4mXw2UY0u4iGpNZt Mw0/mEU8aW1eQ8U6gkjI135NMtjoF2yQulzQDrJvO91U2L/0FYKnsEbJXG4G6BvxOtEd 3kbxrx14WrFx34BDvsySDocn91llSiCVkttlD6UrOvUhujg7cg3ydgG8dRrbMsD6wLwu joWNN1+RhRyHCd3uLcxf7jwUBwz4Rjh+LayDeREwF9ZA42+pE72iiLvAyO0NKakzdvCq tlww== X-Gm-Message-State: ACgBeo0mF5QUcsu3bL/FhsNkmOrz3XF1QHMms1zZaosMryRfTRZ7rBT3 gUJH3Y5NaQS4TvEd5WsYqAP675J451TvmlVRJJY0Myr+Zp6YjqFuhPPpu4y6kpnpaV4kiA1YeEF NXohxVDp4SScZ X-Received: by 2002:a05:600c:35c7:b0:3a3:2612:f823 with SMTP id r7-20020a05600c35c700b003a32612f823mr9706777wmq.33.1659879313166; Sun, 07 Aug 2022 06:35:13 -0700 (PDT) X-Google-Smtp-Source: AA6agR6b3gJMHnoTNtj37IngASsHIWEjuA+66KHlhEYj9gzwpL5gbhYjiJ9U3VuycAq+eyh6uwiMbA== X-Received: by 2002:a05:600c:35c7:b0:3a3:2612:f823 with SMTP id r7-20020a05600c35c700b003a32612f823mr9706761wmq.33.1659879312980; Sun, 07 Aug 2022 06:35:12 -0700 (PDT) Received: from redhat.com ([2.52.21.123]) by smtp.gmail.com with ESMTPSA id y12-20020adfdf0c000000b0021f138e07acsm8993628wrl.35.2022.08.07.06.35.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Aug 2022 06:35:12 -0700 (PDT) Date: Sun, 7 Aug 2022 09:35:07 -0400 From: "Michael S. Tsirkin" To: Christoph Hellwig Cc: Linus Torvalds , Will Deacon , stefanha@redhat.com, jasowang@redhat.com, ascull@google.com, maz@kernel.org, keirf@google.com, jiyong@google.com, kernel-team@android.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, Stefano Garzarella Subject: Re: IOTLB support for vhost/vsock breaks crosvm on Android Message-ID: <20220807092733-mutt-send-email-mst@kernel.org> References: <20220805181105.GA29848@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Sat, Aug 06, 2022 at 11:52:13PM -0700, Christoph Hellwig wrote: > It really is vhost that seems to abuse it so that if the guest > claims it can handle VIRTIO_F_ACCESS_PLATFORM (which every modern > guest should) it enables magic behavior, which I don't think is what > the virtio spec intended. Well the magic behavour happens to be used by QEMU to implement a virtual IOMMU. And when you have a virtual IOMMU you generally want VIRTIO_F_ACCESS_PLATFORM. This is how it came to be reused for that. And since QEMU never passed guest features to vhost unfiltered we never saw the issue even with old QEMU versions on new kernels. It seems natural to pass features unfiltered and we never even said userspace should not do it, so it's quite understandable that this is what corsvm did. -- MST