From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33816) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d6ML0-0000Ya-PI for qemu-devel@nongnu.org; Thu, 04 May 2017 15:22:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d6MKw-0007p0-NZ for qemu-devel@nongnu.org; Thu, 04 May 2017 15:22:54 -0400 Received: from 1.mo5.mail-out.ovh.net ([188.165.57.91]:60499) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1d6MKw-0007oP-Gv for qemu-devel@nongnu.org; Thu, 04 May 2017 15:22:50 -0400 Received: from player786.ha.ovh.net (b6.ovh.net [213.186.33.56]) by mo5.mail-out.ovh.net (Postfix) with ESMTP id 84ADFEADB4 for ; Thu, 4 May 2017 21:22:48 +0200 (CEST) Date: Thu, 4 May 2017 21:22:37 +0200 From: Greg Kurz Message-ID: <20170504212237.341bf8ef@bahia> In-Reply-To: <1493908379.4214.8.camel@redhat.com> References: <20170427072843.8089-1-david@gibson.dropbear.id.au> <1493908379.4214.8.camel@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/+9PD+CfrVxQ/Ta=7JnzivGI"; protocol="application/pgp-signature" Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCHv3 0/4] Clean up compatibility mode handling List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Bolognani Cc: David Gibson , clg@kaod.org, aik@ozlabs.ru, mdroth@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, armbru@redhat.com --Sig_/+9PD+CfrVxQ/Ta=7JnzivGI Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Thu, 04 May 2017 16:32:59 +0200 Andrea Bolognani wrote: > On Thu, 2017-04-27 at 17:28 +1000, David Gibson wrote: > > This is a rebased and revised version of my patches revising CPU > > compatiblity mode handling on ppc, last posted in November.=C2=A0=C2=A0= Since > > then, many of the patches have already been merged (some for 2.9, some > > since).=C2=A0=C2=A0This is what's left. > >=C2=A0 > >=C2=A0=C2=A0* There was conceptual confusion about what a compatibility = mode > >=C2=A0=C2=A0=C2=A0=C2=A0means, and how it interacts with the machine typ= e.=C2=A0=C2=A0This cleans > >=C2=A0=C2=A0=C2=A0=C2=A0that up, clarifying that a compatibility mode (a= s an externally set > >=C2=A0=C2=A0=C2=A0=C2=A0option) only makes sense on machine types that d= on't permit the > >=C2=A0=C2=A0=C2=A0=C2=A0guest hypervisor privilege (i.e. 'pseries') > >=C2=A0 > >=C2=A0=C2=A0* It was previously the user's (or management layer's) respo= nsibility > >=C2=A0=C2=A0=C2=A0=C2=A0to determine compatibility of CPUs on either end= for migration. > >=C2=A0=C2=A0=C2=A0=C2=A0This uses the compatibility modes to check that = properly during an > >=C2=A0=C2=A0=C2=A0=C2=A0incoming migration. =20 >=20 > I started playing with this, mostly with libvirt integration > in mind of course, and quickly ran into a behavior that I > believe was not intentional and unfortunately managed to slip > into 2.9, I assume through the patches which were initially > part of this series (mentioned above). >=20 > More specifically, when I run a guest with >=20 > =C2=A0 -M pseries-2.8 -cpu host >=20 > using QEMU 2.8, the CPU in the guest is reported as >=20 > =C2=A0 POWER8E (raw), altivec supported >=20 > However, when using QEMU 2.9 with the very same command line, > including explicitly using the pseries-2.8 machine type, I > get >=20 > =C2=A0 POWER8 (architected), altivec supported >=20 The goal of this series is indeed to switch from raw to architected but I agree that it shouldn't affect existing machine types. This probably calls for some compat prop. > instead. The same happens with current master + your patches > applied on top. >=20 > I'm not sure how much real trouble that will actually cause > for guests, but it's a guest-visible change as a result of > upgrading QEMU, which should just not happen. >=20 >=20 > I'll keep testing your series and get back to you as soon as > I have more feedback or questions. >=20 > --=C2=A0 > Andrea Bolognani / Red Hat / Virtualization >=20 --Sig_/+9PD+CfrVxQ/Ta=7JnzivGI Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEARECAAYFAlkLf30ACgkQAvw66wEB28IpQgCfSejn80qzOcyUf4UFf1ERbwB7 nNEAnAhe66nNGCKYhJPjjKV+7cnI8IYI =5U8P -----END PGP SIGNATURE----- --Sig_/+9PD+CfrVxQ/Ta=7JnzivGI--