Worked on stabilizing S390x virtualization in the avocado-framework/avocado-vt repository by addressing a device enumeration issue affecting virtio devices in QEMU environments. Focused on system programming and device driver development, the work involved updating the parent bus type to 'virtual-css-bus' for virtio-serial-ccw, vhost-vsock-ccw, and virtio-rng-ccw devices. This targeted bug fix, implemented in Python, resolved missing device numbers and improved the reliability of device enumeration during runtime. The solution enhanced virtualization stability for S390x systems, reducing errors and increasing test reliability, while demonstrating expertise in virtualization technologies and low-level system integration within complex environments.