Re: [PATCH 3/5] kvm: Directly account vtime to system on guest switch

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 25/10/12 09:56, Frederic Weisbecker wrote:
[...]
>>> * s390 doesn't disable irqs in its implementation of vtime_account().
>>> If vtime_account() in kvm races with an irq, the pending time might
>>> be accounted twice. With vtime_account_system_irqsafe() we are protected.
>>
>> We disable irqs before we call kvm_guest_enter/exit, see kvm-s390.c:
>>
>>
>> [...]
>>         if (!kvm_is_ucontrol(vcpu->kvm))
>>                 kvm_s390_deliver_pending_interrupts(vcpu);
>>         vcpu->arch.sie_block->icptcode = 0;
>>         local_irq_disable();
>>         kvm_guest_enter();
>>         local_irq_enable();
>> [...]
>>
> 
> Ah ok. Hmm I still need to keep it irqsafe for the other archs though,
> as it is currently with vtime_account(). So perhaps I can remove your
> local_irq_disable there and use vtime_account_system_irqsafe()
> instead?

Yes. We added the local_irq_disable code just for the vtime accounting.