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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id F2CE1D5CC8A for ; Wed, 30 Oct 2024 10:34:00 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t661J-0007ua-8L; Wed, 30 Oct 2024 06:33:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t661G-0007u8-M7 for qemu-devel@nongnu.org; Wed, 30 Oct 2024 06:33:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t661E-00070T-AG for qemu-devel@nongnu.org; Wed, 30 Oct 2024 06:33:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1730284417; h=from:from:reply-to: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=YKUnc8I63knl+8rDZDnDnCw50ytdt3zFrwBTOs/QWs0=; b=dmtKDHpsemtaWXwiwzmE3/MmYYlKrRniYVsJmWUSqCQZicP7xVKNi1pP7VybT69SvzXseu awLrfwu61nnhiN/YHxQrTsH4LiszazGqbUOEGKA9AgCste2VBeQgLqIgyuAgFYeiKkRpNo W9xfWxiR8qnKK3SnRezSu4HJOkAXXyY= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-257-heYYvHFGOnGDon9-YbMwrg-1; Wed, 30 Oct 2024 06:33:35 -0400 X-MC-Unique: heYYvHFGOnGDon9-YbMwrg-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D0669195608C; Wed, 30 Oct 2024 10:33:33 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.92]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 670C0300018D; Wed, 30 Oct 2024 10:33:26 +0000 (UTC) Date: Wed, 30 Oct 2024 10:33:23 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: qemu-devel@nongnu.org, Markus Armbruster , Peter Maydell , Eduardo Habkost , Paolo Bonzini , Mark Cave-Ayland , Igor Mammedov , "Michael S . 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David Alan Gilbert" , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , =?utf-8?Q?C=C3=A9dric?= Le Goater , Fabiano Rosas , Juraj Marcin Subject: Re: [PATCH RFC v2 5/7] x86/iommu: Make x86-iommu a singleton object Message-ID: References: <20241029211607.2114845-1-peterx@redhat.com> <20241029211607.2114845-6-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20241029211607.2114845-6-peterx@redhat.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.302, 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=-0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Oct 29, 2024 at 05:16:05PM -0400, Peter Xu wrote: > X86 IOMMUs cannot be created more than one on a system yet. Make it a > singleton so it guards the system from accidentally create yet another > IOMMU object when one already presents. > > Now if someone tries to create more than one, e.g., via: > > ./qemu -M q35 -device intel-iommu -device intel-iommu > > The error will change from: > > qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple vIOMMUs for x86 yet. > > To: > > qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports one instance > > Unfortunately, yet we can't remove the singleton check in the machine > hook (pc_machine_device_pre_plug_cb), because there can also be > virtio-iommu involved, which doesn't share a common parent class yet. > > But with this, it should be closer to reach that goal to check singleton by > QOM one day. Looking at the other iommu impls, I noticed that they all have something in common, in that they call pci_setup_iommu from their realize() function to register their set of callback functions. This pci_setup_iommu can happily be called multiple times and just over-writes previously registered callbacks. I wonder if this is a better place to diagnose incorrect usage of multiple impls. If pci_setup_iommu raised an error, it wouldn't matter that virtio-iommu doesn't share a common parent with intel-iommu. This would also perhaps be better for a future heterogeneous machine types, where it might be valid to have multiple iommus concurrently. Checking at the resource setup/registration point reflects where the physical constraint comes from. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|