关于viridian interface
At the moment we provide MSR access to APIC registers, and the hypercall
to yield the CPU when waiting for a spinlock. We looked at a few others
(e.g. address-space-change hypercall) but found the benefits, if any,
were negligible.
The most important part of the interface is that we can use it to tell
Windows not to expect timer interrupt delivery to be as even across all
CPUs as it would be on bare metal. This gets rid of annoying STOP 0x101
bluescreens in multi-vcpu Windows from Vista on.