Re: [PATCH 08/10] Move IO APIC to its own lock.

[Avi Kivity <avi@redhat.com>]

On 08/09/2009 05:57 PM, Gleb Natapov wrote:
> On Sun, Aug 09, 2009 at 05:54:30PM +0300, Avi Kivity wrote:
>    
>> On 08/09/2009 03:41 PM, Gleb Natapov wrote:
>>      
>>> Introduce new function kvm_notifier_set_irq() that should be used
>>> to change irq line level from irq notifiers. When irq notifier
>>> change irq line level it calls into irq chip code recursively. The
>>> function avoids taking a lock recursively.
>>>
>>>        
>> This looks really horrible.  I don't have an alternative yet, but I'll
>> think of one.
>>      
> I agree this is not nice. This is needed only for device assignment
> case. That explains why I don't like device assignment :)

Well, implementation problems can be fixed.  Other issues with device 
assignment cannot.

> The problem
> is that the only communication channel from guest to assigned device that
> goes through the host is interrupt injection/acknowledgement, so we try to
> do things (lowering IRQ) on this path that usually are done somewhere else.
>    

You can queue the injection somehow (work struct? special purpose queue 
examined after unlock?) and avoid the recursive locking.

-- 
error compiling committee.c: too many arguments to function