KVM

Kernel-based Virtual Machine (KVM) is a virtualization infrastructure built into the Linux kernel that enables the kernel to function as a hypervisor. It requires hardware virtualization extensions, such as Intel VT-x or AMD-V, to run guest operating systems with near-native performance. KVM comprises two main components: a loadable kernel module (the KVM module) that provides virtualization primitives and memory management, and a user-space component (commonly QEMU) that handles device emulation and I/O virtualization.

In operation, a guest runs in its own isolated address space, with KVM leveraging the CPU’s virtualization features to switch between host and guest contexts efficiently. QEMU supplies the virtual hardware that the guest sees, while virtio-based devices can offer improved performance through paravirtualization. For advanced I/O, VFIO and the IOMMU enable direct device assignment to guests under controlled conditions.

KVM supports a range of features essential for modern virtualization, including 64-bit guests, symmetric multi-processing with multiple vCPUs, memory ballooning, and overcommitment. It also supports live migration of running guests between hosts, provided the environment uses shared storage and compatible networking. Kernel SamePage Merging (KSM) can reduce memory usage by sharing identical memory pages across VMs. Virtual networks and disks are typically provided by libvirt-managed stacks or QEMU’s device models, with virtio devices offering high performance.

Management and ecosystem tools such as libvirt, virt-manager, OpenStack, and oVirt are commonly used to create, configure, and monitor KVM-based virtual machines. KVM has become a default hypervisor in many Linux-centric data centers, desktop virtualization setups, and cloud platforms, competing with other hypervisors like Xen, VMware ESXi, and Hyper-V.