Libvirt

KVM (Kernel-based Virtual Machine) and QEMU (Quick Emulator) solve different halves of the same problem and are almost always used together. KVM is a Linux kernel module that turns the kernel into a hypervisor: with Intel VT-x or AMD-V, guest CPUs run on real hardware at near-native speed and guest memory is managed through extended page tables. KVM has no device model of its own — no disk, network, or firmware emulation. QEMU supplies that in userspace (virtio, USB, VGA, ACPI) and controls KVM by issuing ioctl calls on /dev/kvm — creating VMs, mapping memory, running vCPUs via KVM_RUN — while QMP exposes external management over a Unix socket. libvirt, originally from Red Hat, sits above both: it translates domain XML into QEMU command lines and lifecycle operations. The stack is the default on Linux: RHEL ships qemu-kvm, OpenShift Virtualization runs KubeVirt (virt-launcher → libvirt → QEMU), and OpenShift Sandboxed Containers uses Kata Containers with the same hypervisor to isolate pods in micro-VMs.