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

On 03/09/2012 03:04 PM, Daniel P. Berrange wrote: >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 ? I don't remember that discussion and really don't think I agree with the conclusion. If libvirt wants to define CPU models on their own, they can. If libvirt wants to use the user's definitions, don't use -nodefconfig. CPU models aren't a QEMU concept. The reason it's in the configuration file is to allow a user to add their own as they see fit. There is no right model names. It's strictly a policy.