RE: [Xen-devel] [PATCH][RFC] pv-ops: fix shared irq device passthrough

["Han, Weidong" <weidong.han@xxxxxxxxx>]

Jeremy Fitzhardinge wrote:
> On 10/30/09 02:29, Han, Weidong wrote:
>> All devices will call probing_irq in startup_pirq, which bind pirq
>> to event channel. But now probing_irq always returns false, then all
>> pirqs are not shareable. In my system, a PCI NIC, an USB controller
>> and an IDE interface device share the same IRQ 18. Because above
>> reason, pirq 18 is set not shareable. So when I hide the PCI NIC,
>> and assign it to guest, it fails in guest_bind_pirq, therefore the
>> PCI NIC in guest cannot work, even impact the devices who share the
>> IRQ 18.       
>> 
>> If don't want to change __setup_irq code like my patch does, current
>> probing_irq is useless (always return false). The problem is there
>> is almost no information in desc can be used in probing_irq if
>> desc->action is NULL. Keir, do you have any ideas?   
>> 
> 
> I think the intent of probing_irq is to detect irqs which are being
> used to probe for an interrupt during driver initialization.  This
> should only be used for things like ISA which don't have any way to
> explicitly find out what irq a device is attached to.
> 
> Given that ISA devices aren't very interesting and no driver should
> need to do that kind of probing under Xen, I wonder if we can't just
> remove the whole test?
> 
>     J

Not only ISA devices, but also PCI devices will use probing_irq. ISA devices 
are indeed not interesting, VT-d only assigns PCI devices. In fact, Sharing 
interrupt between assigned devices and host devices is not happy situation. We 
put much effort to make it work long time ago. If there is really no good 
approach, one alternate is add a limit of device assignment: don't allow assign 
PCI devices which share interrupt with other devices.

Regards,
Weidong
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