1. An apparatus comprising: an execution unit of a processor; and a memory management unit interposed between the execution unit and an interface to memory suitable for storage of both guest page tables maintained by a guest operating system and shadow page tables maintained generally in correspondence with the guest page tables by virtualization logic, the memory management unit configured to walk in-memory data structures that encode the shadow page tables, to access entries of the shadow page tables and, based thereon or on a cached representation of page mappings therein, to perform virtual-to-physical address translations relative to memory targets of instructions executed by the execution unit, the memory management unit responsive to a shadowed write indication coded in association with either an entry of the shadow page tables or a cached representation of a page mapping therein used to perform the virtual-to-physical address translation for a write-type one of the instructions that targets an entry of one of the guest page tables, the memory management unit configured to complete the memory access of the write-type instruction that targets the guest page table entry, and to store in a buffer, information sufficient to allow the virtualization software to later update an entry of the shadow page tables in correspondence therewith.