linux-kernel - Re: [PATCH v3 51/59] KVM: arm/arm64: GICv4: Add doorbell interrupt handling

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Date:   Thu, 31 Aug 2017 09:19:15 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Christoffer Dall <cdall@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Eric Auger <eric.auger@...hat.com>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v3 51/59] KVM: arm/arm64: GICv4: Add doorbell interrupt
 handling

On 30/08/17 21:58, Christoffer Dall wrote:
> On Wed, Aug 30, 2017 at 04:36:06PM +0100, Marc Zyngier wrote:
>> On 28/08/17 19:18, Christoffer Dall wrote:
>>> On Mon, Jul 31, 2017 at 06:26:29PM +0100, Marc Zyngier wrote:
>>>> When a vPE is not running, a VLPI being made pending results in a
>>>> doorbell interrupt being delivered. Let's handle this interrupt
>>>> and update the pending_last flag that indicates that VLPIs are
>>>> pending. The corresponding vcpu is also kicked into action.
>>>>
>>>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
>>>> ---
>>>>  virt/kvm/arm/vgic/vgic-v4.c | 34 ++++++++++++++++++++++++++++++++++
>>>>  1 file changed, 34 insertions(+)
>>>>
>>>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
>>>> index 534d3051a078..6af3cde6d7d4 100644
>>>> --- a/virt/kvm/arm/vgic/vgic-v4.c
>>>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
>>>> @@ -21,6 +21,19 @@
>>>>  
>>>>  #include "vgic.h"
>>>>  
>>>> +static irqreturn_t vgic_v4_doorbell_handler(int irq, void *info)
>>>> +{
>>>> +	struct kvm_vcpu *vcpu = info;
>>>> +
>>>> +	if (!kvm_vgic_vcpu_pending_irq(vcpu)) {
>>>> +		vcpu->arch.vgic_cpu.vgic_v3.its_vpe.pending_last = true;
>>>> +		kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
>>>> +		kvm_vcpu_kick(vcpu);
>>>> +	}
>>>
>>> Can this ever fire while vgic_v4_init() is running and before te rest of
>>> the system has been properly initialized with some entertaining results
>>> to follow?  (I'm not sure if spurious doorbell non-resident vPE
>>> interrupts is a thing or not).
>>
>> It could if you only had this patch. The following patch makes sure that
>> the interrupt does not get enabled at request time, meaning it will only
>> get enabled when the vcpu will eventually block.
>>
>> And yes, spurious doorbells are a real thing. And they suck.
>>
> 
> Ah, my abilities to forward read on a patch series are quite poor.
Not quite. It indicates that the patch split is a bit wrong, and that

	irq_set_status_flags(irq, IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY);

should really be in this patch and not the following one.

I'll fix that as I rebase the whole thing.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...