Comment 8 for bug 1908512

Hi,
first of all thanks for your report!

Trying to recreate your issue I've downloaded the same ubuntu-20.04.1-live-server-amd64.iso to a focal and a hirsute host system.
Then I've defined the qcow2 and XML you posted on those.

$ wget https://mirrors.ocf.berkeley.edu/ubuntu-releases/20.04/ubuntu-20.04.1-live-server-amd64.iso
$ qemu-img create -f qcow2 /var/lib/libvirt/images/disk0.qcow2 10G
$ virsh define ubuntu-server.xml

Just as you reported and one would expect there s no difference between the two other than the UUID and the default machine type.

Both VMs start fine from a libvirt/qemu POV.

Since recently libvirt 6-9 and qemu 5.2 migrated my "new" case also has
-machine pc-i440fx-hirsute,accel=kvm,usb=off,dump-guest-core=off,memory-backend=pc.ram \
-object memory-backend-ram,id=pc.ram,size=2147483648 \

But still very similar to your report so far.

The important VNC and display config in both cases is:
-vnc 0.0.0.0:1 \
-device cirrus-vga,id=video0,bus=pci.0,addr=0x2 \

Note: Cirrus is embarrassingly old, but is and will stay the default for compatibility. Never the less I'd recommend using QXL - at least for any Linux guests these days.

Connecting VNC to those two guests confirms your report.
The one running under Focal fails with "Could not allocate memory. boot" the one under Hirsute works fine.