From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44798) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VddxU-0001av-83 for qemu-devel@nongnu.org; Tue, 05 Nov 2013 05:34:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VddxO-0007mD-0u for qemu-devel@nongnu.org; Tue, 05 Nov 2013 05:34:04 -0500 Message-ID: <5278C980.7020009@redhat.com> Date: Tue, 05 Nov 2013 11:33:36 +0100 From: Paolo Bonzini 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> <7A574FE1-8AC8-46DB-B978-330ED2AD4428@suse.de> In-Reply-To: <7A574FE1-8AC8-46DB-B978-330ED2AD4428@suse.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] spapr: add "compat" machine option List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: Nikunj A Dadhania , Alexey Kardashevskiy , QEMU Developers , "list@suse.de:PReP" , Paul Mackerras , =?ISO-8859-1?Q?Andreas_?= =?ISO-8859-1?Q?F=E4rber?= Il 05/11/2013 11:27, Alexander Graf ha scritto: > > On 05.11.2013, at 10:52, Paolo Bonzini wrote: > >> 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 real >>>>> PVR from the hardware (which it may not support but this is why we need >>>>> compatibility mode). >>>> >>>> How do you support migration from a newer to an older CPU then? I think >>>> 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 change 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. >> >> Still in my opinion it should be "-cpu", not "-machine". Even if it's >> just a "virtual" CPU model. > > The only thing that this really changes is an SPR (MSR in x86 speech) > on an existing cpu model. It's definitely not a new CPU type. If > anything it'd be an option to an existing type. Agreed. Paolo