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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 16/10/2009 09:35, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:

>>> 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?
>> 
>> Why does host hang? Only the assigned interrupt will block, and that's
>> exactly what the guest wants :-)
> 
> Hypervisor shouldn't EOI the real vector until guest EOI the corresponding
> virtual vector , right ?  Not sure.:-)

If the EOI is via the local APIC, which I suppose it must be, then a timeout
fallback probably is required. This is because priorities are assigned
arbitrarily to guest interrupts, and a non-EOIed interrupt blocks any
lower-priority interrupts. In particular, some of those could be owned by
dom0 for example, and be quite critical to forward progress of the entire
system.

 -- Keir



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