[libvirt] specifying cirrus ram size

Hi, In order to migrate a VM from an older system with qemu-kvm to a newer one with qemu, the newer qemu needs to be told to use the same vga ram size as qemu-kvm used, 8M. virsh domxml-from-native suggests that the way to specify a 8mb cirrus vga ram size would be to add <qemu:commandline> <qemu:arg value='-global'/> <qemu:arg value='cirrus-vga.vgamem_mb=8'/> </qemu:commandline> However whenever I edit a .xml to add this, it disappears. I'm adding it right before the ending </domain> Am I doing something silly? thanks, -serge