1. A method for protecting the integrity of a set of memory pages to be accessed by an operating system of a data processing system, the method comprising: running the operating system in a virtual machine (VM) of the data processing system; verifying the integrity of the set of memory pages on loading of pages in the set to a memory of the data processing system for access by the operating system; in response to verification of the integrity, designating the set of memory pages as trusted pages and, in a page table to be used by the operating system during the access, marking non-trusted pages as paged; and in response to a subsequent page fault interrupt for a non-trusted page, remapping the set of pages to a region of the data processing system memory which is inaccessible to the virtual machine (VM).