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RE: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)

He, Qing wrote:
> On Fri, 2009-10-16 at 15:32 +0800, Zhang, Xiantao wrote:
>> According to the description, the issue should be caused by lost EOI
>> write for the MSI interrupt and leads to permanent interrupt mask.
>> There should be a race between guest setting new vector and  EOIs
>> old vector for the interrupt.  Once guest sets new vector before it
>> EOIs the old vector, hypervisor can't find the pirq which
>> corresponds old vector(has changed 
>> to new vector) , so also can't EOI the old vector forever in hardware
>> level. Since the corresponding vector in real processor can't be
>> EOIed, 
>> so system may lose all interrupts and result the reported issues
>> ultimately. 
>> But I remembered there should be a timer to handle this case
>> through a forcible EOI write to the real processor after timeout,
>> but seems it doesn't function in the expected way.
> The EOI timer is supposed to deal with the irq sharing problem,
> since MSI doesn't share, this timer will not be started in the
> case of MSI.

That maybe a problem if so. If a malicious/buggy guest won't EOI the MSI 
vector, so host may hang due to lack of timeout mechanism? 

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