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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 BFB7AC433E0 for ; Wed, 20 Jan 2021 10:02:53 +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 F267C2332A for ; Wed, 20 Jan 2021 10:02:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F267C2332A 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]:40670 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l2AKB-0007HX-RY for qemu-devel@archiver.kernel.org; Wed, 20 Jan 2021 05:02:51 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:57936) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l2AJG-0006g5-3H for qemu-devel@nongnu.org; Wed, 20 Jan 2021 05:01:54 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:24367) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l2AJE-0008RA-94 for qemu-devel@nongnu.org; Wed, 20 Jan 2021 05:01:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611136911; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xBmn5rXy1sZ9VgaRuqxwboS9UWPASujNK3PF+nhNFlI=; b=cwGb12oDT/yeJMJAPEps6QjDNCL7vabz18+fthmyu8EUC1M/0rU73KISRk5gkSkJ3l1CW5 olyMkOFOV1EzuPEy4ik4BLcGK3vDcnMVnR1nL3oS7puDedsoZHiUBdHzANlD8nbWjN+nPO rw5ZvgItEFy5EQYB5ndxPeslzkm4h2w= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-43-9Qz1_iIoPlmehkE9FqMFrw-1; Wed, 20 Jan 2021 05:01:46 -0500 X-MC-Unique: 9Qz1_iIoPlmehkE9FqMFrw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6131059; Wed, 20 Jan 2021 10:01:45 +0000 (UTC) Received: from localhost (unknown [10.40.208.9]) by smtp.corp.redhat.com (Postfix) with ESMTP id E84A019CA8; Wed, 20 Jan 2021 10:01:39 +0000 (UTC) Date: Wed, 20 Jan 2021 11:01:37 +0100 From: Igor Mammedov To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: [RFC PATCH 0/2] x86 CPU feature +/- fiddling and +kvm-no-defaults Message-ID: <20210120110137.1830cec9@redhat.com> In-Reply-To: <20210119164142.GO2335568@redhat.com> References: <20210119142207.3443123-1-david.edmondson@oracle.com> <20210119162826.GL2335568@redhat.com> <20210119163518.GH1227584@habkost.net> <20210119164142.GO2335568@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=imammedo@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.195, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , Eduardo Habkost , "Michael S. Tsirkin" , Richard Henderson , qemu-devel@nongnu.org, Markus Armbruster , David Edmondson , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 19 Jan 2021 16:41:42 +0000 Daniel P. Berrang=C3=A9 wrote: > On Tue, Jan 19, 2021 at 11:35:18AM -0500, Eduardo Habkost wrote: > > On Tue, Jan 19, 2021 at 04:28:26PM +0000, Daniel P. Berrang=C3=A9 wrote= : =20 > > > On Tue, Jan 19, 2021 at 02:22:05PM +0000, David Edmondson wrote: =20 > > > > Currently "-cpu -feature,+feature" will disable -feature, which see= ms > > > > contrary to the intention of the user. Fix this such that the later > > > > flag wins. There are no changes to the interaction of +/- and =3Don= /=3Doff. =20 > > >=20 > > > The -feature/+feature syntax is the legacy way of configuring > > > features, with feature=3Don|off being the preferred, since that match= es > > > the general QEMU standard for boolean properties. > > >=20 > > > Your proposed change in ordering of + vs - makes conceptual sense, bu= t > > > it is none the less a semantic change in behaviour that may well caus= e > > > breakage for existing deployed VMs. This impacts guest ABI so could > > > particularly cause live migration problems. > > >=20 > > > IOW, we should have implemented it the way you propose in the first > > > place, but I don't think it is safe to change it now, unless you can > > > tie that new semantic to a machine type version. > > >=20 > > > Before we consider that though, Paolo has just deprecated many of the > > > legacy approaches for boolean properties in this: > > >=20 > > > https://lists.nongnu.org/archive/html/qemu-devel/2021-01/msg04341.h= tml > > >=20 > > > I'm inclined to say that we just follow on from that and finally > > > deprecate the +feature/-feature CPU syntax which we're already consid= ering > > > legacy. This would remove the need to care about changing its behavio= ur =20 > >=20 > > I believe we had multiple proposal in the past do deprecate > > +feature/-feature, but there were objections. I couldn't find > > the original threads, though. =20 >=20 > Historically libvirt was using +/- syntax, but we finally removed the las= t > usage of it in June 2019 / libvirt v5.4.0. So for modern QEMU libvirt wil= l > always use =3Don|off. there are KVM unit tests that used /- syntax, I don't recall any attempt to switch to canonical syntax. >=20 > > In either case, I thought we had already deprecated the weird > > ordering rules of "-feature,+feature". =20 >=20 > Regards, > Daniel