Re: [RFC PATCH 3/4] KVM: x86: Add EOI exit bitmap inference

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-05-13 15:04, Paolo Bonzini wrote:
> 
> 
> On 13/05/2015 12:25, Jan Kiszka wrote:
>>>>> But perhaps when enabling KVM_SPLIT_IRQCHIP we can use args[0] to pass
>>>>> the number of IOAPIC routes that will cause EOI exits?
>>>>
>>>> And you need to ensure that their routes can be found in the table
>>>> directly. Given IOAPIC hotplug, that may not be the first ones there...
>>>
>>> Can you reserve a bunch of GSIs at the beginning of the GSI space, and
>>> use rt->map[] to access them and build the EOI exit bitmap?
>>
>> Ideally, userspace could give the kernel a hint where to look. It has a
>> copy of the routing table and manages it, no?
> 
> Well, reserving space at the beginning of the table (and communicating
> the size via KVM_ENABLE_CAP is a way to "give the kernel a hint where to
> look".  Perhaps not the best, but simple and supports hotplug to some
> extent.

But then we need at least a way to differentiate between IOAPIC and MSI
routes so that the loop can actually stop when hitting the first
non-IOAPIC entry. Right now, this is not possible. But even that would
be a kind of ugly interface.

Jan

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