Re: KVM handling external interrupts

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

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On 2012-06-07 10:13, Jan Kiszka wrote:
> On 2012-06-07 09:51, Abel Gordon wrote:
>>> 3> if we configure not exit on external interrupt by setting some
>>> field in VMCS, what will happen during the physical interrupts? will
>>> the CPU use the guest IDT for response interrupt? If so, can KVM
>>> redirect the CPU to use another IDT for guest (assuming modifying the
>>> IDTR)?
>>
>> Yes, that's exactly something we already did in a research project.
>> You can read our paper published in ASPLOS 2012: ELI: Bare-metal
>> performance for I/O virtualization
>> (
>> http://dl.acm.org/citation.cfm?id=2151020&dl=ACM&coll=DL&CFID=86701665&CFTOKEN=26302003
> 
> Interesting. Can you provide it publicly (or send a version privately)?

Sorry, should have googled first:

http://www.mulix.org/pubs/eli/eli.pdf :)

> 
>> )
>>
>> Note this is not so simple, there are many other issues you should
>> consider.
> 
> Is it just complicated, not upstreamable, or are the unsolved issues
> like security holes or the need to paravirtualize the guest?

My first feeling is that it's not easily upstreamable due to the need to
fiddle with the host's IDT, specifically on VCPU task migration. But I
need to read the requirements of this more carefully. Still interesting
work!

Jan

> 
> I'm still hoping that Intel/AMD will finally enable this in hardware, at
> least for MSIs. Providing direct injection for legacy line-base
> interrupts is likely not worth the silicon and bits (would require some
> hw-assisted IOAPIC instead of just a bit more APIC virtualization).
> 
> Jan



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