  This paper introduces a type system for resource management in the context of
nested virtualization. With nested virtualization, virtual machines compete
with other processes for the resources of their host environment in order to
provision their own processes, which could again be virtual machines. The
calculus of virtually timed ambients formalizes such resource provisioning,
extending the capabilities of mobile ambients to model the dynamic creation,
migration, and destruction of virtual machines. The proposed type system uses
assumptions about the outside of a virtually timed ambient to guarantee
resource provisioning on the inside. We prove subject reduction and progress
for well-typed virtually timed ambients, expressing that upper bounds on
resource needs are preserved by reduction and that processes do not run out of
resources.
