Hypercall - XenA hypercall is to a syscall what a hypervisor is to an OS. Alternatively, a hypercall is to a hypervisor what a syscall is to a kernel. A hypercall is a software trap from a domain to the hypervisor, just as a syscall is a software trap from an application to the kernel. Domains will use hypercalls to request privileged operations like updating pagetables. Like a syscall, the hypercall is synchron
