Re: KVM handling external interrupts

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

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On 2012-06-07 13:05, Abel Gordon wrote:
> 
> 
> Jan Kiszka <jan.kiszka@web.de> wrote on 07/06/2012 13:51:19:
> 
>>>> 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!
>>>
>>> You don't need to fiddle with the host's IDT, you need to fiddle with
>>> the shadow IDT and interrupt vector mapping/remapping.
>>
>> Yes, but you need to sync the host IDT into the shadow table. This may
>> require some hooks in generic code to avoid scanning the host table on
>> each guest entry.
> 
> Well, the shadow IDT only needs to be synced with interrupts coming from
> assigned devices. The rest of the entries doesn't matter, they just
> generate an exception. Once they generate an exception, they are delivered
> through the host IDT. So, all you need to know are the vectors assigned
> to the guest to build the shadow IDT.

Not totally true. If the host decides to allocate some new vector that
collides with some guest usage, you need to rearrange the shadow IDT and
the physical IRQ routing. So you need to track what the host does.

Jan


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