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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 BF737C433FF for ; Wed, 31 Jul 2019 21:23:33 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 97F1120679 for ; Wed, 31 Jul 2019 21:23:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97F1120679 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 ([::1]:44662 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hsw4K-000878-Ud for qemu-devel@archiver.kernel.org; Wed, 31 Jul 2019 17:23:32 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46425) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hsw3q-0007iP-I7 for qemu-devel@nongnu.org; Wed, 31 Jul 2019 17:23:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hsw3p-0000lF-Gk for qemu-devel@nongnu.org; Wed, 31 Jul 2019 17:23:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5451) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hsw3p-0000kX-Ah for qemu-devel@nongnu.org; Wed, 31 Jul 2019 17:23:01 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 47662308FB93; Wed, 31 Jul 2019 21:22:59 +0000 (UTC) Received: from localhost (ovpn-116-22.gru2.redhat.com [10.97.116.22]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9A34C19C5B; Wed, 31 Jul 2019 21:22:54 +0000 (UTC) Date: Wed, 31 Jul 2019 18:22:52 -0300 From: Eduardo Habkost To: Sergio Lopez Message-ID: <20190731212252.GW4313@habkost.net> References: <20190729125755.45008-1-slp@redhat.com> <20190730042004-mutt-send-email-mst@kernel.org> <87ftmmwg0e.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ftmmwg0e.fsf@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Wed, 31 Jul 2019 21:22:59 +0000 (UTC) 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] [RFC] virtio-mmio: implement modern (v2) personality (virtio-1) X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org, "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 31, 2019 at 02:22:09PM +0200, Sergio Lopez wrote: > > Michael S. Tsirkin writes: > > > On Mon, Jul 29, 2019 at 02:57:55PM +0200, Sergio Lopez wrote: > >> Implement the modern (v2) personality, according to the VirtIO 1.0 > >> specification. > >> > >> Support for v2 among guests is not as widespread as it'd be > >> desirable. While the Linux driver has had it for a while, support is > >> missing, at least, from Tianocore EDK II, NetBSD and FreeBSD. > > > > The fact that there was no open source hypervisor implementation has > > probably contributed to this :) > > > >> For this reason, the v2 personality is disabled, keeping the legacy > >> behavior as default. > > > > I agree it's a good default for existing machine types. > > > >> Machine types willing to use v2, can enable it > >> using MachineClass's compat_props. > > > > Hmm. Are compat_props really the recommended mechanism to > > tweak defaults? I was under the impression it's > > only for compatibility with old machine types. > > Eduardo, any opinion on this? > > Stefan suggested using something like "-global virtio-mmio.modern=true" > which does the trick for the command line, but I'd also like a way to > set it to true by default on microvm. We can discuss the best way to > achieve that (if using compat_props isn't acceptable) on the next > microvm patch series. Compatibility is the most common use case, but IMO compat_props can be used for other kinds of machine-specific defaults. It's better than burying defaults inside non-introspectable machine initialization functions. -- Eduardo