Linux 2.6.20 was released this week with KVM included, so I tried booting a small guest rather than merely reading patches. The first attempt failed immediately because the processor’s virtualisation support was disabled in the firmware. Progress began with entering setup, which keeps systems programming humble.

KVM uses the processor’s hardware virtualisation extensions and exposes a kernel interface through /dev/kvm. A user-space program supplies the virtual machine’s device model and asks the kernel to run virtual CPUs. This is not a complete machine monitor appearing from one kernel option; kernel and user space divide the work.

The basic checks on this Intel test box were:

grep vmx /proc/cpuinfo
modprobe kvm
modprobe kvm-intel
ls -l /dev/kvm

On an AMD processor I would look for svm and use the corresponding module. Seeing the flag is necessary but not always sufficient, because firmware can still disable the facility.

After loading the modules, I launched a guest image with the available QEMU KVM support and watched the kernel log in another terminal. The guest booted, though virtual disk and network performance are not conclusions I can draw from ten minutes and one ageing drive.

I prefer this architecture because putting CPU execution support behind a kernel interface lets normal Linux scheduling and memory management participate, while device emulation remains in user space where a failure is less likely to take the host with it. The caveat is that the boundary can impose overhead, hardware support varies, and young interfaces may change as use exposes mistakes.

Security deserves restraint too. Hardware isolation is not a promise that a hostile guest can never escape. Device emulation processes parse guest-controlled input, and kernel code now manages another complicated processor mode. I am treating guests as isolated test systems, not as magical bags into which all risk disappears.

The useful result today is narrow: with 2.6.20, suitable hardware, enabled firmware support, kernel modules, and matching user space, a Linux host can run a hardware-assisted guest. Whether KVM becomes the preferred general solution will depend on performance, management tools, and how gracefully it handles less cooperative machines.

For now it boots. In infrastructure experiments, reaching a login prompt is the traditional point at which confidence rises faster than evidence.