Re: KVM handling external interrupts

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-06-07 14:32, Abel Gordon wrote:
> kvm-owner@vger.kernel.org wrote on 07/06/2012 15:19:14:
> 
>>>> The guest can still mask interrupts above that limit via cli, no?
>>>> So the only measures that save us from CPU hogging guests are the
>>>> preemption timer and kicking via NMI. Or what am I missing?
>>>
>>> Nothing :) As we described in the paper, this is what we do to avoid
>>> this situation.
>>
>> So the other measures are redundant, right? They only seem to complicate
>> the approach without any gain, that is my point.
> 
> We described in the paper all the mechanisms we thought could be used.

Which of them did you implement and validate so far?

> Which mechanisms are sufficient/preferable/simpler ?  I think we are back
> to the KVM<->Linux dependencies and whenever we are talking about
> hypervisors in general or a specific implementation for KVM.

I don't think this depends on KVM vs. whatever hypervisor, these are
pretty generic considerations.

If you need the preemption timer for breaking out of cli anyway, why
play tricks with off-limit vectors? NMIs can be useful to accelerate the
preemption when some other core wants to deliver an IPI (to kick the
target out of guest mode and to reenable interrupts, not to process them).

Jan


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