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Re: [libvirt] Modern CPU models cannot be used with libvirt



On Fri, Mar 09, 2012 at 05:56:52PM -0300, Eduardo Habkost wrote:
> Resurrecting an old thread:
> 
> I didn't see any clear conclusion in this thread (this is why I am
> resurrecting it), except that many were arguing that libvirt should
> simply copy and/or generate the CPU model definitions from Qemu. I
> really don't think it's reasonable to expect that.
> 
> On Thu, Dec 15, 2011 at 03:54:15PM +0100, Jiri Denemark wrote:
> > Hi,
> > 
> > Recently I realized that all modern CPU models defined in
> > /etc/qemu/target-x86_64.conf are useless when qemu is used through libvirt.
> > That's because we start qemu with -nodefconfig which results in qemu ignoring
> > that file with CPU model definitions. We have a very good reason for using
> > -nodefconfig because we need to control the ABI presented to a guest OS and we
> > don't want any configuration file that can contain lots of things including
> > device definitions to be read by qemu. However, we would really like the new
> > CPU models to be understood by qemu even if used through libvirt. What would
> > be the best way to solve this?
> > 
> > I suspect this could have been already discussed in the past but obviously a
> > workable solution was either not found or just not implemented.
> 
> So, our problem today is basically:
> 
> A) libvirt uses -nodefconfig;
> B) -nodefconfig makes Qemu not load the config file containing the CPU
>    model definitions; and
> C) libvirt expects the full CPU model list from Qemu to be available.

I could have sworn we had this discussion a year ago or so, and had decided
that the default CPU models would be in something like /usr/share/qemu/cpu-x86_64.conf
and loaded regardless of the -nodefconfig setting. /etc/qemu/target-x86_64.conf
would be solely for end user configuration changes, not for QEMU builtin
defaults.

But looking at the code in QEMU, it doesn't seem we ever implemented this ?

Daniel
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