Re: [libvirt] [PATCH 2/4] PowerPC : Add support for launching VMs in 'compat' mode.
On Fri, Oct 10, 2014 at 03:42:41PM +0530, Prerna Saxena wrote:
>From 7228aacaa4b24907b1cbf33838ada8fb81890419 Mon Sep 17 00:00:00 2001
From: Prerna Saxena <prerna(a)linux.vnet.ibm.com>
Date: Tue, 7 Oct 2014 10:53:08 +0530
PowerISA allows processors to run VMs in binary compatibility ("compat")
mode supporting an older version of ISA. QEMU has recently added support to
explicitly denote a VM running in compatibility mode through commit 6d9412ea
& 8dfa3a5e85.
Now, a "compat" mode VM can be run by invoking this qemu commandline on a
POWER8 host: -cpu host,compat=power7.
If this is using 'host'
This patch allows libvirt to extend the "fallback" semantics of cpu model to
describe this new mode for PowerKVM guests.
As an example:
When a user wants to request a power7 vm to run in compatibility mode on
a Power8 host, this can be described in XML as follows :
<cpu mode='custom' match='exact'>
<model fallback='compat'>power7</model>
</cpu>
Then I don't think this should be using mode='custom', but rather it
should be 'host-passthrough'. We would use the <model> to denote the
compatibility mode for the host passthrough. IOW, it feels like this
is better described as
<cpu mode='host-passthrough' match='exact'>
<model>power7</model>
</cpu>
Regards,
Daniel
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