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

[Alexander Graf <agraf@suse.de>]

On 11.08.14 14:27, Eric Auger wrote:
> 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 <eric.auger@linaro.org>
>>>>> ---
>>>>>     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 ;-)

Yeah, please only set it when the kernel exposes that it supports irqfd ;).


Alex