What is KVM?

Why KVM matters

Because a KVM guest runs its own kernel, it can load kernel modules, run non-Linux operating systems, use real swap and support nested virtualisation. Memory allocated to a KVM guest is genuinely reserved, which is the practical difference from container-based virtualisation.

KVM in practice

When you run a KVM server, the first thing you check is /proc/cpuinfo in the guest — if it doesn't match the host's flags, you're likely seeing paravirtualised shortcuts, not full KVM. You set memory allocation with real reservations: overcommit will make the guest's OOM killer fire while the host looks idle. If you misconfigure nested virtualisation, you lose hardware-assisted paging and guests run at a fraction of the speed. Getting it wrong costs you performance you can't recover without a reboot.

What people get wrong about KVM

People assume KVM is the same as OpenVZ or LXC because both use the Linux kernel. The correction is that KVM gives each guest its own kernel, whereas containers share the host's kernel. You can load kernel modules and run non-Linux OSes only on KVM. Shared-namespace isolation isn't hardware-enforced.