On 20.02.15 15:12, Paolo Bonzini wrote:

On 20/02/2015 14:45, Alexander Graf wrote:

quoted

On 18.02.15 10:32, Bogdan Purcareata wrote:

quoted

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.

Thomas, what is the usual approach for patches like this? Do you take
them into your rt tree or should they get integrated to upstream?

Patch 1 is definitely suitable for upstream, that's the reason why we
have raw_spin_lock vs. raw_spin_unlock.

I see, perfect :).

Bogdan, please resend patch 1 with CC to kvm-ppc@vger so that I can pick
it up from patchworks.


Alex