1. A method, comprising: storing at least a portion of an executable application program in a host system physical memory at a first host physical address; instrumenting a copy of said portion of said executable application program and storing said instrumented copy in said host system physical memory at a second host physical address; setting a corresponding access permission to read only for said first host physical address and setting a corresponding access permission to execute only for said second host physical address; and executing said instrumented copy or reading said portion of said executable application program based, at least in part, on said access permissions.