Cache-based Covert Channel
 Cache load measurements create very effective covert channels between cooperating processes running in different VMs.
In practise, this is not a major threat for current deployments since in most cases the cooperating processes can simply talk to each other over a network.
However, covert channels become significant when communication is forbidden by information flow control (IFC) mechanisms such as sandboxing and IFC kernels. The latter is a promissing emerging approach to improving security (e.g., web-server functionality).
 explains more on the covert-channel in Section 8.1.
 Hey, You, Get Off of My Cloud: Exploring Information Leakage in Third-Party Compute Clouds, by Restenpart, T. et al., in CCS09