On 31 July 2014 18:21, Paolo Bonzini [off-list ref] wrote:

What does ARM do if you have a WFI while interrupts are disabled?  On
x86 after "cli;hlt" only an NMI will wake you up.  With spurious
wakeups, it's pretty much guaranteed that you will break such "cli;hlt"
sequences.

The architecture mandates some things that *must* wake you from
a WFI, but it also allows wakeups for other reasons not listed, or
for no reason at all. It's perfectly valid to implement WFI as a NOP
(though it would not be very good for power efficiency, obviously).
Guests which don't surround WFI with a "check whether we should
just go back to WFI" loop are buggy.

thanks
-- PMM