Re: [PATCH v4 3/9] KVM: Clear assigned guest IRQ on release

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

Am 09.11.2010 11:58, Avi Kivity wrote:
> On 11/08/2010 01:21 PM, Jan Kiszka wrote:
>> When we deassign a guest IRQ, clear the potentially asserted guest line.
>> There might be no chance for the guest to do this, specifically if we
>> switch from INTx to MSI mode.
>>
>> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>> ---
>>   virt/kvm/assigned-dev.c |    3 +++
>>   1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
>> index 7c98928..ecc4419 100644
>> --- a/virt/kvm/assigned-dev.c
>> +++ b/virt/kvm/assigned-dev.c
>> @@ -141,6 +141,9 @@ static void deassign_guest_irq(struct kvm *kvm,
>>   	kvm_unregister_irq_ack_notifier(kvm,&assigned_dev->ack_notifier);
>>   	assigned_dev->ack_notifier.gsi = -1;
>>
>> +	kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
>> +		    assigned_dev->guest_irq, 0);
>> +
>>   	if (assigned_dev->irq_source_id != -1)
>>   		kvm_free_irq_source_id(kvm, assigned_dev->irq_source_id);
>>   	assigned_dev->irq_source_id = -1;
> 
> I guess this can't hurt.  Did you see it happen in practice?

Yes, with prefer_msi=off and an e1000e-driven NIC: The legacy IRQ stayed
asserted when the guest actually enabled MSI.

Jan

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