Hypervisors must isolate memories of guest operating systems. This paper is concerned with proving memory isolation properties about the virtualization of the memory management unit provided by a hypervisor through shadow page tables. We conduct the proofs using abstraction techniques between high-level and low-level descriptions of the system, based on techniques from previous work on formally proving memory isolation in micro-kernels. The present paper shows how a hypervisor developed by Technische Universität Berlin has been formalized and presents the isolation properties we have proved on the targeted abstract model. In particular, we provide details about how the management of page tables has been formally modeled.