Re: RFC/patch portability: split kvm_vm_ioctl v3

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Carsten Otte wrote:
>
>>> In addition, I would love to be able to specify which target CPUs 
>>> may receive that interrupt because our IPI equivalent comes out just 
>>> like a regular interrupt on just one target CPU.
>>>
>>> That boils down to something like this:
>>> struct kvm_interrupt_data {
>>>     __u64     interrupt_number;
>>>     cpuset_t possible_target_cpus;
>>> }
>>> and an KVM_INJECT_INTERRUPT common ioctl for the vm to provide this.
>>
>> Are cpusets exported to userspace?
>>
>> x86 has something similar (IPI to a set of cpus) but it's handled 
>> 100% in the kernel these days.
>>
> No they are'nt. We'd need to come up with a different data structure 
> for that.

A bitmap would do it, but what size?  Expandable ones are messy.

> Does IPI have an interrupt number too?

No, it's a command (mmio) to the APIC, you tell it which vector you want 
and to which cpus you want it delivered.  So you can have many IPI 
interrupt vectors.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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