I tore my hair out for a while after rebooting into 6.2 because none of the VM guests would start. After trying lots of things, like down grading qemu-kvm (which fixed it when I upgraded via the CR repository and didn't this time), cloning a VM, and even beginning to create new VM to restore from backup. Luckily I discovered that there is a log for each VM and found in each case it failed because vmvga is not compiled into KVM. So I changed them all to cirrus via virt-manager and they all work again. The host machine is all up to date and all of the guest start and operate as usual. Emmett