I can think of two different interpretations of your question:
1) How much of the time was the Linux VM idle?
2) How much of the time was the Linux VM running code?
The answer to question #1 is that your Linux VM isn't idle. The fact that Linux thinks that it is 100% busy means that it was idle 0% of the time.
The answer to question #2 is 60-70%. The VPs of your Linux VM were running 60-70% of the time.
Perhaps you're asking a third question: Why are my Linux virtual processors only running 60-70% of the time?
To answer that, you'd have to look at other factors. Perhaps there are other VMs eating up time. Perhaps the Linux VM doesn't have paravirtual drivers (Integration Components) installed and its VPs are pausing because they are attempting to interact with "fully virtualized" hardware, which means that they're trying to do I/O and other operations in a way that would be appropriate for a physical machine and the hypervisor is spending time emulating those physical machine aspects.