On Thu, Jul 07, 2016 at 11:42:15AM +0200, Peter Zijlstra wrote:

I suspect you want something like so; except this has holes in.

We clear KVM_ST_PAD_PREEMPT before disabling preemption and we set it
after enabling it, this means that if we get preempted in between, the
vcpu is reported as running even though it very much is not.

Fixing that requires much larger surgery.

Note that this same hole is already a 'problem' for steal time
accounting. The thread can accrue further delays (iow steal time) after
we've called record_steal_time(). These delays will go unaccounted.