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=-2.4 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 7F6E5C072AF for ; Tue, 21 May 2019 09:26:30 +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 173E521783 for ; Tue, 21 May 2019 09:26:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 173E521783 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]:50047 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hT12T-0001Gv-6H for qemu-devel@archiver.kernel.org; Tue, 21 May 2019 05:26:29 -0400 Received: from eggs.gnu.org ([209.51.188.92]:37301) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hT0ze-0008Iz-LJ for qemu-devel@nongnu.org; Tue, 21 May 2019 05:23:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hT0zd-0000uD-B2 for qemu-devel@nongnu.org; Tue, 21 May 2019 05:23:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33718) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hT0zd-0000tA-2x for qemu-devel@nongnu.org; Tue, 21 May 2019 05:23:33 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 661BE87642; Tue, 21 May 2019 09:23:32 +0000 (UTC) Received: from redhat.com (ovpn-112-26.ams2.redhat.com [10.36.112.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 493B8100200D; Tue, 21 May 2019 09:23:26 +0000 (UTC) Date: Tue, 21 May 2019 10:23:22 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eduardo Habkost Message-ID: <20190521092322.GG25835@redhat.com> References: <20190215103239.28640-1-berrange@redhat.com> <20190215103239.28640-2-berrange@redhat.com> <20190517190129.GA17245@habkost.net> <20190520095611.GD21976@redhat.com> <20190520205959.GC10764@habkost.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190520205959.GC10764@habkost.net> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 21 May 2019 09:23:32 +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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Gonglei , "Michael S. Tsirkin" , Gerd Hoffmann , Andreas =?utf-8?Q?F=C3=A4rber?= , 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 05:59:59PM -0300, Eduardo Habkost wrote: > On Mon, May 20, 2019 at 10:56:11AM +0100, Daniel P. Berrang=C3=A9 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=C3=A9 w= rote: > > > > A number of virtio devices (gpu, crypto, mouse, keyboard, tablet)= only > > > > support the virtio-1 (aka modern) mode. Currently if the user lau= nches > > > > QEMU, setting those devices to enable legacy mode, QEMU will sile= ntly > > > > create them in modern mode, ignoring the user's (mistaken) reques= t. > > > >=20 > > > > This patch introduces proper data validation so that an attempt t= o > > > > configure a virtio-1-only devices in legacy mode gets reported as= an > > > > error to the user. > > > >=20 > > > > Checking this required introduction of a new field to explicitly = track > > > > what operating model is to be used for a device, separately from = the > > > > 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. >=20 > Oh, that's the information I was missing. Thanks! >=20 > >=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. >=20 > 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. Yes, that would be a desirable thing todo in future to get the error checking done sooner in virtio_pci_realize() only. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|