On an arch 2.06 hypervisor, a pending perfmon interrupt will be delivered
to the hypervisor at any point the guest is running, regardless of
MSR[EE].  In order to reflect this interrupt, the hypervisor has to mask
the interrupt in PMGC0 -- and set MSRP[PMMP] to intercept futher guest
accesses to the PMRs to detect when to unmask (and prevent the guest from
unmasking early, or seeing inconsistent state).

This has the side effect of ignoring any changes the guest makes to
MSR[PMM], so wait until after the interrupt is clear, and thus the
hypervisor should have cleared MSRP[PMMP], before setting MSR[PMM].  The
counters wil not actually run until PMGC0[FAC] is cleared in
pmc_start_ctrs(), so this will not reduce the effectiveness of PMM.
Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>