Re: [Qemu-devel] [PATCH v5 08/10] hw/intc/arm_gic_kvm: advertise irqfd

[Eric Auger]

On 08/11/2014 02:05 PM, Alexander Graf wrote:
> 
> On 11.08.14 14:04, Eric Auger wrote:
>> On 08/11/2014 11:37 AM, Alexander Graf wrote:
>>> On 09.08.14 16:25, Eric Auger wrote:
>>>> set kvm_irqfds_allowed
>>>>
>>>> Signed-off-by: Eric Auger <address@hidden>
>>>> ---
>>>>    hw/intc/arm_gic_kvm.c | 2 ++
>>>>    1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/hw/intc/arm_gic_kvm.c b/hw/intc/arm_gic_kvm.c
>>>> index 5038885..08b7bf9 100644
>>>> --- a/hw/intc/arm_gic_kvm.c
>>>> +++ b/hw/intc/arm_gic_kvm.c
>>>> @@ -576,6 +576,8 @@ static void kvm_arm_gic_realize(DeviceState *dev,
>>>> Error **errp)
>>>>                                KVM_DEV_ARM_VGIC_GRP_ADDR,
>>>>                                KVM_VGIC_V2_ADDR_TYPE_CPU,
>>>>                                s->dev_fd);
>>>> +
>>>> +    kvm_irqfds_allowed = true;
>>> Is this always true? If it is, why not enable it separately while making
>>> vhost-net work for example?
>> Hi Alex,
>>
>> yes I think so. As soon as KVM is enabled, KVM/arm would enable
>> injection though irqfd. Defintively makes sense to test it with
>> vhost-net too. Well a matter of priority ;-)
> 
> More a matter of accuracy. What if you use new QEMU on old KVM which
> does have in-kernel GIC support, but no irqfd support?

Hi Alex,

VFIO device code also calls kvm_check_extension(kvm_state,
KVM_CAP_IRQFD_RESAMPLE) which would return false if IRQFD is not enabled
in old kernels. But with respect to vhost-net irqfd usage I cannot
comment yet and you may be right ;-)

Best Regards

Eric
> 
> 
> Alex
>