Linux KVM

KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT-x or AMD-V). Developed as a Linux kernel module first merged in Linux 2.6.20 (February 2007) by Avi Kivity at Qumranet (later acquired by Red Hat), KVM transforms the Linux kernel into a Type-1 hypervisor while maintaining the full Linux scheduler, memory management, and device drivers. KVM enables each virtual machine to run unmodified guest operating systems (Linux, Windows, BSD, Solaris) with near-native performance by executing guest CPU instructions directly on the host CPU via hardware virtualization extensions. The KVM architecture consists of: a loadable kernel module (kvm.ko) providing core virtualization infrastructure, architecture-specific modules (kvm-intel.ko for VT-x, kvm-amd.ko for AMD-V), and a userspace component (typically QEMU) that handles device emulation, disk I/O, network I/O, and the virtual machine monitor lifecycle. Key features include: hardware-assisted paging (EPT on Intel, NPT/RVI on AMD) eliminating shadow page table overhead, nested virtualization (running KVM inside KVM guests), SR-IOV (Single Root I/O Virtualization) for direct PCI device assignment with near-bare-metal I/O performance, VFIO (Virtual Function I/O) for GPU and device passthrough, vCPU hotplug, memory hotplug, transparent huge page support, live migration between physical hosts with minimal downtime, VirtIO framework for paravirtualized device drivers (disk, network, balloon, console, SCSI, RNG, GPU, input), KSM (Kernel Samepage Merging) for memory deduplication of identical guest pages, and real-time scheduling support for latency-sensitive workloads. KVM powers major cloud platforms including Google Compute Engine, OVHcloud, DigitalOcean, and OpenStack-based private clouds.