From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46221) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vdcan-0005zH-TU for qemu-devel@nongnu.org; Tue, 05 Nov 2013 04:06:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Vdcaf-00049b-Fa for qemu-devel@nongnu.org; Tue, 05 Nov 2013 04:06:33 -0500 Sender: Paolo Bonzini Message-ID: <5278B4FC.6020503@redhat.com> Date: Tue, 05 Nov 2013 10:06:04 +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> In-Reply-To: <5249754E.6070308@ozlabs.ru> 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: Alexey Kardashevskiy Cc: Nikunj A Dadhania , Alexander Graf , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Paul Mackerras , =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= 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. Paolo > 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.