Re: [Qemu-devel] [PATCH 2/6] kvm: Rename kvm_irqchip_set_irq to kvm_inject_async_irq

[Jan Kiszka]

On 2012-07-25 18:41, Peter Maydell wrote:
> On 25 July 2012 17:28, Jan Kiszka <address@hidden> wrote:
>> On 2012-07-25 18:24, Peter Maydell wrote:
>>> ...incidentally I was thinking about maybe moving kvm_irqchip_create()
>>> from being called by kvm_init() to being called by the device
>>> init function for the relevant irqchip (particularly we'll need
>>> to do that if we adopt Avi's suggestion of having a parameter
>>> to KVM_CREATE_IRQCHIP to specify a particular kind of irqchip).
>>> But that's more invasive surgery so I didn't want to do it yet.
>>
>> This won't fly as irchip affects the whole orchestra (vcpus & irqchip
>> stubs in user space), at least on x86, and has to be called in the
>> current order. That's also why kernel_irqchip is a machine options, not
>> an option of one of the many device models.
> 
> Yes, one of the things you'd need to do is move actual creation
> of the vcpus (as opposed to the QEMU CPU QOM objects) to rather
> later in the sequence than they are now.

KVM VCPU creation is bound to the QOM object creation phase if we want
hotplugging support.

> 
> Where you have multiple devices which all need to go the same way
> you can put that in the machine model code and then have all the
> devices take an option the machine model sets to say which way
> they go.
> 
> (Oddities in the x86 specific bits of the KVM kernel code ought
> to result in oddities in x86 specific bits of QEMU, not in
> generic bits :-))

I dreamed of this as well before porting in-kernel irqchip support
upstream. ;)

But the point of this service is not that arch-specific in fact: By the
time you have a set of kernel irqchips that cannot reasonably be
instantiated / enabled separately, a single service helps to avoid that
userspace tries to do this mistake at all. Not all archs may have this
requirement, but a generic service needs to address it if it wants to be
generic.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux