Re: [PATCH v2 4/4] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices

[Jan Kiszka <jan.kiszka@siemens.com>]

Am 02.11.2010 19:54, Michael S. Tsirkin wrote:
> On Tue, Nov 02, 2010 at 07:51:39PM +0100, Jan Kiszka wrote:
>> Am 02.11.2010 19:48, Jan Kiszka wrote:
>>> Am 02.11.2010 19:40, Jan Kiszka wrote:
>>>>>>>> @@ -199,6 +343,13 @@ static void kvm_free_assigned_device(struct kvm *kvm,
>>>>>>>>  
>>>>>>>>  	pci_reset_function(assigned_dev->dev);
>>>>>>>>  
>>>>>>>> +	/*
>>>>>>>> +	 * Unmask the IRQ at PCI level once the reset is done - the next user
>>>>>>>> +	 * may not expect the IRQ being masked.
>>>>>>>> +	 */
>>>>>>>> +	if (assigned_dev->pci_2_3)
>>>>>>>> +		pci_2_3_irq_unmask(assigned_dev->dev);
>>>>>>>> +
>>>>>>>
>>>>>>> Doesn't pci_reset_function clear mask bit? It seems to ...
>>>>>>
>>>>>> I was left with non-functional devices for the host here if I was not
>>>>>> doing this. Need to recheck, but I think it was required.
>>>>>
>>>>> Interesting. Could you check why please?
>>>>>
>>>>
>>>> Can't reproduce anymore. This was early code, maybe affected by some
>>>> bits or buts that no longer exist.
>>>>
>>>> Spec says it's cleared on reset, so I removed those lines now.
>>>>
>>>
>>> Hmpf, it just happened again: Guest was using my ath9k, I killed the
>>> guest, lspci says DisINTx+. Strange. Is anyone (qemu) restoring the
>>> config space after the reset, bringing the disable bit back?
>>
>> Or does the kernel cache the control word?
>>
>> Jan
> 
> Maybe it does, need to dig in drivers/pci. If it does this
> might have other implications.

OK, that mystery is resolved now: pci_reset_function saves & restores
the device state.

Jan

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