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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 AA03BC04AAC for ; Mon, 20 May 2019 21:01:36 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 870702171F for ; Mon, 20 May 2019 21:01:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 870702171F 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 ([127.0.0.1]:41858 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hSpPb-0007hB-Pf for qemu-devel@archiver.kernel.org; Mon, 20 May 2019 17:01:35 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49206) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hSpOV-0007IZ-FT for qemu-devel@nongnu.org; Mon, 20 May 2019 17:00:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hSpOT-00082Q-8o for qemu-devel@nongnu.org; Mon, 20 May 2019 17:00:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50198) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hSpOR-000815-GC for qemu-devel@nongnu.org; Mon, 20 May 2019 17:00:24 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E383EF74CC; Mon, 20 May 2019 21:00:14 +0000 (UTC) Received: from localhost (ovpn-116-14.gru2.redhat.com [10.97.116.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id C9B305DF27; Mon, 20 May 2019 21:00:06 +0000 (UTC) Date: Mon, 20 May 2019 17:59:59 -0300 From: Eduardo Habkost To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Message-ID: <20190520205959.GC10764@habkost.net> References: <20190215103239.28640-1-berrange@redhat.com> <20190215103239.28640-2-berrange@redhat.com> <20190517190129.GA17245@habkost.net> <20190520095611.GD21976@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20190520095611.GD21976@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Mon, 20 May 2019 21:00:20 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 1/2] hw: report invalid disable-legacy|modern usage for virtio-1-only devs X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Gonglei , "Michael S. Tsirkin" , Gerd Hoffmann , Andreas =?iso-8859-1?Q?F=E4rber?= , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, May 20, 2019 at 10:56:11AM +0100, Daniel P. Berrang=E9 wrote: > On Fri, May 17, 2019 at 04:01:29PM -0300, Eduardo Habkost wrote: > > Hi, > >=20 > > Sorry for taking so long to look at this more closely: > >=20 > > On Fri, Feb 15, 2019 at 10:32:38AM +0000, Daniel P. Berrang=E9 wrote: > > > A number of virtio devices (gpu, crypto, mouse, keyboard, tablet) o= nly > > > support the virtio-1 (aka modern) mode. Currently if the user launc= hes > > > QEMU, setting those devices to enable legacy mode, QEMU will silent= ly > > > create them in modern mode, ignoring the user's (mistaken) request. > > >=20 > > > This patch introduces proper data validation so that an attempt to > > > configure a virtio-1-only devices in legacy mode gets reported as a= n > > > error to the user. > > >=20 > > > Checking this required introduction of a new field to explicitly tr= ack > > > what operating model is to be used for a device, separately from th= e > > > disable_modern and disable_legacy fields that record the user's > > > requested configuration. > >=20 > > I'm still trying to understand why we need to add a new field. > >=20 > > If disable_modern, disable_legacy and mode are always expected to > > be consistent with each other, why do we need another field? > >=20 > > If they are not always consistent with each other, when exactly > > do we want them to be inconsistent, and why? >=20 > The pain point is that we're using the existing variables to record > two distinct pieces of information >=20 > - The user's request for modern vs legacy > - The PCI bus requirements for modern vs legacy >=20 > The existing code would overwrite the user's setting for > "disable_legacy" when deciding whether the device is in > a PCI or PCIe port. This happens in virtio_pci_realize. >=20 > We can only report errors with the user's requested config > after the sub-classes call virtio_pci_force_virtio_1, but > this doesn't happen until virtio_${subclass}_pci_release. >=20 > So by the time we're able to report errors, virtio_pci_realize > has already overwritten the user's disable_legacy setting, so > we've lost the very piece of info we need to check to report > errors with. Oh, that's the information I was missing. Thanks! >=20 > Given the ordering of virtio_pci_realize vs the calls > to virtio_pci_force_virtio_1 by subclasses, I don't see any > option other than to use separate variables for the two > distinct pieces of information. We could replace the virtio_pci_force_virtio_1() calls with a new VirtioDeviceClass::virtio_1_only boolean field, to be handled by virtio_pci_realize() before overriding disable_legacy. But this can be done as a follow up patch, so: Reviewed-by: Eduardo Habkost --=20 Eduardo