Re: [libvirt] [PATCH] i386: Re-add "pconfig" CPUID flag name

On Thu, Sep 26, 2019 at 09:42:20PM -0300, Eduardo Habkost wrote: > (CCing libvir-list) > > On Thu, Sep 26, 2019 at 11:58:30PM +0200, Paolo Bonzini wrote: > > Is this really needed? QEMU's value of pconfig=on vs. off should be > > provided by QMP CPU model queries, if a property is not available then > > Libvirt should not try to set it to off. > > > > Libvirt can easily work around it for new VMs, and it should. > > The issue are VMs that were created with QEMU 3.1.0. QEMU 3.1.0 > was telling libvirt "Icelake-Server can't be used unless > pconfig=off is used", and libvirt was adding pconfig=off to the > domain XML as expected. > > It would be wrong for libvirt to remove a device option when > migrating an existing VM to another QEMU version. We can change > the rules (and document that), but do we want to? IIUC currently any existing VMs with Icelake-Server will *not* have pconfig present, since libvirt is going to set pconfig=off QEMU has now dropped pconfig CPUID entirely. If libvirt were to stop setting pconfig=off, then there is NO guest ABI change, so we'd be safe in that sense.