Вот что сам проксмокс говорит:
You may sometimes encounter the term KVM (Kernel-based Virtual Machine). It means that Qemu is running with the support of the virtualization processor extensions, via the Linux KVM module. In the context of Proxmox VE Qemuand KVM can be used interchangeably, as Qemu in Proxmox VE will always try to load the KVM module.