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

[Bogdan Purcareata]

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: introduces a limit on the maximum VCPUs a guest can have, in order to
prevent 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. Not sure if it's best to send it upstream and
have a hanging CONFIG_PREEMPT_RT_FULL check there, with no effect, or send it
against linux-stable-rt. Please apply as you consider appropriate.

- applied & compiled against upstream 3.19
- applied & compiled against stable-rt 3.14-rt (0002 with minor fuzz)

Bogdan Purcareata (2):
  powerpc/kvm: Convert openpic lock to raw_spinlock
  powerpc/kvm: Limit MAX_VCPUS for guests running on RT Linux

 arch/powerpc/include/asm/kvm_host.h |  6 +++++
 arch/powerpc/kvm/mpic.c             | 44 ++++++++++++++++++-------------------
 2 files changed, 28 insertions(+), 22 deletions(-)

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2.1.4