From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:41865)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rkrcmar@redhat.com>) id 1Z5su6-0001JU-2n
	for qemu-devel@nongnu.org; Fri, 19 Jun 2015 05:48:07 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rkrcmar@redhat.com>) id 1Z5su1-0008PN-Ts
	for qemu-devel@nongnu.org; Fri, 19 Jun 2015 05:48:06 -0400
Received: from mx1.redhat.com ([209.132.183.28]:54546)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rkrcmar@redhat.com>) id 1Z5su1-0008PF-OE
	for qemu-devel@nongnu.org; Fri, 19 Jun 2015 05:48:01 -0400
Date: Fri, 19 Jun 2015 11:47:57 +0200
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Message-ID: <20150619094756.GB10217@potion.brq.redhat.com>
References: <1434641064-8405-1-git-send-email-rkrcmar@redhat.com>
	<1434641064-8405-3-git-send-email-rkrcmar@redhat.com>
	<20150618155046.GC3874@thinpad.lan.raisama.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20150618155046.GC3874@thinpad.lan.raisama.net>
Content-Transfer-Encoding: quoted-printable
Subject: Re: [Qemu-devel] [PATCH 2/2] target-i386: automatically raise cpuid
	level to 0xd
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: pbonzini@redhat.com, bsd@redhat.com, qemu-devel@nongnu.org, rth@twiddle.net

2015-06-18 12:50-0300, Eduardo Habkost:
> On Thu, Jun 18, 2015 at 05:24:24PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99 w=
rote:
> > We already bump to level 7 if features there are requested, so do the
> > same for 0xD.
> >=20
> > Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com>
>=20
> This breaks guest ABI and live-migration, as CPUID data is not part of
> the migration stream (although we have considered including it in the
> future).
>=20
> If we are going to add more special cases like this, we must provide a
> way to make QEMU honour an explicit "level" option from the config file
> or command-line.

Thanks, I'll drop this patch.

> I have considered introducing "min-[x]level" and "max-{x]level"
> properties to control automatic increasing of level/xlevel. The existin=
g
> X86CPUDefinition.level field could just control min_level, while
> explicit "level=3D" on the command-line or config file would explicitly
> force a specific value. Probably setting "max-level" on machine-type
> compat code would be enough to restore the previous behavior.

We'd need to set min-level at least to 7, to capture the raising we do
now, but a feature in level between default and 7 would result in a
different behavior, so we need to make it much uglier :/
We can add 'compat-level' bit for old machine types and raise to highest
habited function otherwise, optionally with controls you described.