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

From: Alexander Graf <[email-masked]>
Date: Fri, 20 Feb 2015 15:16:06 +0100

On 20.02.15 15:12, Paolo Bonzini wrote:
> 
> 
> On 20/02/2015 14:45, Alexander Graf wrote:
>>
>>
>> On 18.02.15 10:32, Bogdan Purcareata wrote:
>>> 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