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 3DAD8D43341 for ; Thu, 7 Nov 2024 11:12:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t90R4-0006mH-D9; Thu, 07 Nov 2024 06:12:22 -0500 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 1t90R1-0006m0-UB for qemu-devel@nongnu.org; Thu, 07 Nov 2024 06:12:19 -0500 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 1t90R0-00037z-9O for qemu-devel@nongnu.org; Thu, 07 Nov 2024 06:12:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1730977936; 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=U2wqDeV1Qpz0fvd9HvyBAYczWy3MVuSZhQJP7XT82CU=; b=AJ0EJjR0umZCjVgSiwvS+TjLYh9c/NOCjhL7vZLge7wVnD3zXLzms9gOmKFC019JR7E3K2 kWk3YU+916nvTw1O36pcPyvVjBcz6S1qGnoyRrkYQ6RP4JPSM+qADXVolFn/z17COeTdKL z88YiJmHMdWXgH0eC3kAKzOEcTMJ5w8= Received: from mx-prod-mc-03.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-669-2J1LqFMTP92C6ZSvY75EDg-1; Thu, 07 Nov 2024 06:12:15 -0500 X-MC-Unique: 2J1LqFMTP92C6ZSvY75EDg-1 X-Mimecast-MFC-AGG-ID: 2J1LqFMTP92C6ZSvY75EDg Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 14BD719560B8; Thu, 7 Nov 2024 11:12:14 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.150]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 78276195E480; Thu, 7 Nov 2024 11:12:12 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4AE6F21E6A28; Thu, 7 Nov 2024 12:12:10 +0100 (CET) From: Markus Armbruster To: Peter Xu Cc: qemu-devel@nongnu.org, Fabiano Rosas , Igor Mammedov , Juraj Marcin , "Michael S . Tsirkin" , "Dr . David Alan Gilbert" , =?utf-8?Q?C=C3=A9dric?= Le Goater , Eduardo Habkost , Daniel P . =?utf-8?Q?Berrang=C3=A9?= , Alex Williamson , Paolo Bonzini , Peter Maydell Subject: Re: [PATCH 2/4] x86/iommu: Make x86-iommu a singleton object In-Reply-To: (Peter Xu's message of "Fri, 25 Oct 2024 18:13:25 -0400") References: <20241024165627.1372621-1-peterx@redhat.com> <20241024165627.1372621-3-peterx@redhat.com> <87jzdwlekc.fsf@pond.sub.org> Date: Thu, 07 Nov 2024 12:12:10 +0100 Message-ID: <87jzdfl2lx.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@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=-0.34, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Xu writes: > On Fri, Oct 25, 2024 at 05:55:59PM -0400, Peter Xu wrote: >> On Fri, Oct 25, 2024 at 11:25:23AM +0200, Markus Armbruster wrote: >> > Peter Xu writes: >> > >> > > 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. >> > > >> > > Signed-off-by: Peter Xu >> > >> > $ qemu-system-x86_64 -device amd-iommu,help >> > /work/armbru/qemu/include/hw/boards.h:24:MACHINE: Object 0x56473906f960 is not an instance of type machine >> > Aborted (core dumped) [...] >> Thanks for the report! >> >> It turns out that qdev_get_machine() cannot be invoked too early, and the >> singleton code can make it earlier.. >> >> We may want a pre-requisite patch to allow qdev_get_machine() to be invoked >> anytime, like: >> >> ===8<=== >> diff --git a/hw/core/qdev.c b/hw/core/qdev.c >> index db36f54d91..7ceae47139 100644 >> --- a/hw/core/qdev.c >> +++ b/hw/core/qdev.c >> @@ -831,6 +831,16 @@ Object *qdev_get_machine(void) >> { >> static Object *dev; >> >> + if (!phase_check(PHASE_MACHINE_CREATED)) { >> + /* >> + * When the machine is not created, below can wrongly create >> + * /machine to be a container.. this enables qdev_get_machine() to >> + * be used at any time and return NULL properly when machine is not >> + * created. >> + */ >> + return NULL; >> + } >> + >> if (dev == NULL) { >> dev = container_get(object_get_root(), "/machine"); >> } >> ===8<=== >> >> I hope it makes sense on its own. > > My apologies, spoke too soon here. This helper is used too after machine > is created, but right before switching to PHASE_MACHINE_CREATE stage.. container_get() is a trap. When the object to be gotten is always "container", it merely complicates container creation: it's implicitly created on first get. Which of the calls creates may be less than obvious. When the object to be gotten is something else, such as a machine, container_get() before creation is *wrong*, and will lead to trouble later. In my opinion: * Hiding creation in getters is a bad idea unless creation has no material side effects. * Getting anything but a container with container_get() is in bad taste. > So we need another way, like: > > ===8<=== > > diff --git a/hw/core/qdev.c b/hw/core/qdev.c > index db36f54d91..36a9fdb428 100644 > --- a/hw/core/qdev.c > +++ b/hw/core/qdev.c > @@ -832,7 +832,13 @@ Object *qdev_get_machine(void) > static Object *dev; > > if (dev == NULL) { > - dev = container_get(object_get_root(), "/machine"); > + /* > + * NOTE: dev can keep being NULL if machine is not yet created! > + * In which case the function will properly return NULL. > + * > + * Whenever machine object is created and found once, we cache it. > + */ > + dev = object_resolve_path_component(object_get_root(), "machine"); > } > > return dev; Now returns null instead of a bogus container when called before machine creation. Improvement of sorts. But none of the callers expect null... shouldn't we assert(dev) here? Hmm, below you add a caller that checks for null. Another nice mess. > ===8<=== > > The idea is still the same. Meanwhile I'll test more to see whether it has > other issues. > > Thanks, > >> Then callers who can be invoked earlier >> could then handle NULL properly, in this case.. >> >> ===8<=== >> diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c >> index 4bfeb08705..fceb7adfe0 100644 >> --- a/hw/i386/x86-iommu.c >> +++ b/hw/i386/x86-iommu.c >> @@ -80,9 +80,15 @@ void x86_iommu_irq_to_msi_message(X86IOMMUIrq *irq, MSIMessage *msg_out) >> >> X86IOMMUState *x86_iommu_get_default(void) >> { >> - MachineState *ms = MACHINE(qdev_get_machine()); >> - PCMachineState *pcms = >> - PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE)); >> + Object *machine = qdev_get_machine(); >> + PCMachineState *pcms; >> + >> + /* If machine has not been created, so is the vIOMMU */ >> + if (!machine) { >> + return NULL; >> + } >> + >> + pcms = PC_MACHINE(object_dynamic_cast(machine, TYPE_PC_MACHINE)); >> >> if (pcms && >> object_dynamic_cast(OBJECT(pcms->iommu), TYPE_X86_IOMMU_DEVICE)) { >> ===8<=== >> >> I'll make sure this works if I'll repost. >> >> Thanks, >> >> -- >> Peter Xu