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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

Paolo