[PATCH v2 0/2] powerpc/kvm: Enable running guests on RT Linux

[Bogdan Purcareata <bogdan.purcareata@freescale.com>]

This patchset enables running KVM SMP guests with external interrupts on an
underlying RT-enabled Linux. Previous to this patch, a guest with in-kernel MPIC
emulation could easily panic the kernel due to preemption when delivering IPIs
and external interrupts, because of the openpic spinlock becoming a sleeping
mutex on PREEMPT_RT_FULL Linux.

0001: converts the openpic spinlock to a raw spinlock, in order to circumvent
this behavior. While this change is targeted for a RT enabled Linux, it has no
effect on upstream kvm-ppc, so send it upstream for better future maintenance.

0002: disables in-kernel MPIC emulation for guest running on RT, in order to
prevent a potential DoS attack due to large system latencies. This patch is
targeted to RT (due to CONFIG_PREEMPT_RT_FULL), but it can also be applied on
upstream Linux, with no effect.

- applied & compiled against vanilla 4.0
- applied & compiled against stable-rt 3.18-rt

v2:
- updated commit messages
- change the fix for potentially large latencies from limiting the max number of
  VCPUs a guest can have to disabling the in-kernel MPIC

Bogdan Purcareata (2):
  powerpc/kvm: Convert openpic lock to raw_spinlock
  powerpc/kvm: Disable in-kernel MPIC emulation for PREEMPT_RT_FULL

 arch/powerpc/kvm/Kconfig |  1 +
 arch/powerpc/kvm/mpic.c  | 44 ++++++++++++++++++++++----------------------
 2 files changed, 23 insertions(+), 22 deletions(-)

-- 
2.1.4