It appears that the hypervisor leaks data from one VM to another by not clearing a cache. If that is all, this leak can be fixed by explicitly clearing the cache when switching to another VM. This will probably cost a few CPU cycles (and cause a few extra cache misses when a VM is resumed).
I'm still waiting for ThinkGeek (or a similar outfit) to start selling an electric pencil sharpener that fits in a standard drive slot of my PC and is powered from the PSU of the PC. Keeping the wood and graphite particles away from the innards of the computer may pose a problem.
It's a poor workman who blames his tools.