This is obviously not a scientifically valid assessment, but it is my general early impressions. This started as a really really long slack message, but it became pretty clear that slack wasn’t the right place for something like this — so here it is as a blog post instead.
I was talking to a friend the other day about our shared mutual appreciation of virtio-vsock, and it made me wonder something. How do virtual machines on Linux actually work? I know it involves qemu and the kernel’s KVM virtual machine implementation, but exactly how do they interact? How does the kernel get qemu to do emulation tasks as required?
qemu is several things hanging out together in a trench coat, but one of those things is software which can configure Linux’s built-in KVM virtual machine functionality to run a virtual machine, and then handle emulation of the devices that virtual machine is attached to which cannot be represented with actual physical hardware. This part of qemu is called a “KVM client” in the Linux kernel documentation. Its called that because if we ignore the emulation part for now it is just literally a client calling established APIs to the Linux kernel.