From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45904) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VQd3H-00065r-JV for qemu-devel@nongnu.org; Mon, 30 Sep 2013 08:58:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VQd3A-0005gb-9b for qemu-devel@nongnu.org; Mon, 30 Sep 2013 08:58:15 -0400 Received: from mail-pd0-f174.google.com ([209.85.192.174]:61620) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VQd3A-0005gM-3s for qemu-devel@nongnu.org; Mon, 30 Sep 2013 08:58:08 -0400 Received: by mail-pd0-f174.google.com with SMTP id y13so5591077pdi.5 for ; Mon, 30 Sep 2013 05:58:06 -0700 (PDT) Message-ID: <5249754E.6070308@ozlabs.ru> Date: Mon, 30 Sep 2013 22:57:50 +1000 From: Alexey Kardashevskiy 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> In-Reply-To: <52496601.6040500@redhat.com> Content-Type: text/plain; charset=UTF-8 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: Paolo Bonzini , Alexander Graf Cc: Paul Mackerras , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, Nikunj A Dadhania , =?UTF-8?B?QW5kcmU=?= =?UTF-8?B?YXMgRsOkcmJlcg==?= On 30.09.2013 21:52, Paolo Bonzini wrote: > Il 30/09/2013 13:25, Alexander Graf ha scritto: >> On 27.09.2013, at 10:06, Alexey Kardashevskiy wrote: >> >>>> To be able to boot on newer hardware that the software support, >>>> PowerISA defines a logical PVR, one per every PowerISA specification >>>> version from 2.04. >>>> >>>> This adds the "compat" option which takes values 205 or 206 and forces >>>> QEMU to boot the guest with a logical PVR (CPU_POWERPC_LOGICAL_2_05 or >>>> CPU_POWERPC_LOGICAL_2_06). >>>> >>>> The guest reads the logical PVR value from "cpu-version" property of >>>> a CPU device node. >>>> > > 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). It is possible to run QEMU with -cpu POWER8 with some old distro which does not know about power8, it will switch to power6-compat mode, the the user does "yum update" (or analog) and then the new kernel (with power8 support) will do H_CAS again and this time "raw" power8 should be selected. -- With best regards Alexey Kardashevskiy -- icq: 52150396