From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45604) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vdh4Q-00056Q-Ic for qemu-devel@nongnu.org; Tue, 05 Nov 2013 08:53:33 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Vdh4J-0006er-7O for qemu-devel@nongnu.org; Tue, 05 Nov 2013 08:53:26 -0500 Message-ID: <5278F84A.2010904@suse.de> Date: Tue, 05 Nov 2013 14:53:14 +0100 From: =?ISO-8859-1?Q?Andreas_F=E4rber?= MIME-Version: 1.0 References: <1380269200-8194-1-git-send-email-aik@ozlabs.ru> <67325DB7-EF06-49CD-BA79-6B44BCC20140@suse.de> <52496601.6040500@redhat.com> <5249754E.6070308@ozlabs.ru> <5278B4FC.6020503@redhat.com> <2B4B8088-FED7-43C5-A12F-2BDDDAB2A863@suse.de> <5278BFF0.8010004@redhat.com> In-Reply-To: <5278BFF0.8010004@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] spapr: add "compat" machine option List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , Alexander Graf Cc: Peter Maydell , Nikunj A Dadhania , Alexey Kardashevskiy , QEMU Developers , Blue Swirl , qemu-ppc , Igor Mammedov , Paul Mackerras Am 05.11.2013 10:52, schrieb Paolo Bonzini: > Il 05/11/2013 10:16, Alexander Graf ha scritto: >> >> On 05.11.2013, at 10:06, Paolo Bonzini wrote: >> >>> Il 30/09/2013 14:57, Alexey Kardashevskiy ha scritto: >>>>>> Why is the option under -machine instead of -cpu? >>>> Because it is still the same CPU and the guest will still read the r= eal >>>> PVR from the hardware (which it may not support but this is why we n= eed >>>> compatibility mode). >>> >>> How do you support migration from a newer to an older CPU then? I th= ink >>> the guest should never see anything about the hardware CPU model. >> >> POWER can't model that. It always leaks the host CPU information into = the guest. It's the guest kernel's responsibility to not expose that chan= ge to user space. >> >> Yes, it's broken :). I'm not even sure there is any sensible way to do= live migration between different CPU types. >=20 > Still in my opinion it should be "-cpu", not "-machine". Even if it's > just a "virtual" CPU model. PowerPC currently does not have -cpu option parsing. If you need to implement it, I would ask for a generic hook in CPUClass set by TYPE_POWERPC_CPU, so that the logic does not get hardcoded in cpu_init, and for the p=3Dv parsing logic to be so generic as to just set property = p to value v on the CPU instance. I.e. please make the compatibility settings a static property or dynamic property of the CPU. Maybe the parsing code could even live in generic qom/cpu.c, overridden by x86/sparc and reused for arm? Somewhere down my to-do list but patches appreciated... Andreas --=20 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imend=F6rffer; HRB 16746 AG N=FCrnbe= rg