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Re: [Qemu-devel] [PATCH] spapr: add "compat" machine option


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] spapr: add "compat" machine option
Date: Tue, 05 Nov 2013 10:06:04 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9

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.




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