I just upgraded to 6.12.0-2 today and none of my QEMU/KVM virtual machines will boot. I have a Windows 10 VM without passthrough, a Windows 10 VM with GPU/USB/SATA passthrough, and A Windows 11 VM with GPU passthrough, and all of them halt after displaying the TianoCore boot message. There’s no spinning wheel, no errors in dmesg or the logs, and no errors displayed when launching the VMs from the command line.
The LTS kernel, 6.6.61, launches the VMs as always, so there’s definitely a bug with kernel 6.12 QEMU/KVM somewhere.