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Re: [Xen-devel] [PATCH] VMX: wbinvd when vmentry under UC

On 29/11/13 14:31, Liu, Jinsong wrote:
> Andrew Cooper wrote:
>> On 29/11/13 14:15, Liu, Jinsong wrote:
>>> Jan Beulich wrote:
>>>>>>> "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> 11/28/13 8:17 AM >>>
>>>>> Liu, Jinsong wrote:
>>>>>> Yes. reprogram_timer here just delay timer a little slot, say,
>>>>>> 1~2ms. I think it's OK, i.e. at any point of wbinvd() operation at
>>>>>> hypervisor, or any irq disabled area, timer interrupt in fact also
>>>>>> has good chance to be delayed some time -- however at
>>>>>> TIMER_SOFTIRQ, all expired thing would be executed, and
>>>>>> re-calculated and set next time point via reprogram_timer --
>>>>>> that's OK. 
>>>>> Comments/thoughts about this option?
>>>> Apart from continuing to be very uncertain that this won't have any
>>>> bad side effects, I'm also rather concerned that you deal with one
>>>> special case interrupt here, ignoring other potentially high rate
>>>> ones (like such coming from NICs). 
>>>> Jan
>>> Considering this, seems adding flag is the only work around way
>>> since high freq interrupt would result in dead-like-loop. My concern
>>> of adding flag is it's not easy to clean every possible path,
>>> especially future extension.   
>>> Or, do not support vt-d w/o snoop.
>>> Thanks,
>>> Jinsong
>> Do you know how many systems have vt-d without snoop ?
>> ~Andrew
> Yes, that's what I need check inside Intel. Maybe not feasible idea I agree.
> Thanks,
> Jinsong

Given that PCIPassthrough realistically involves requiring trusting the
guest administrator, it might be feasible to have another iommu= option
of "allow passthough even without snoop".


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