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