Subject: [PATCH 10/10] KVM: arm/arm64: vgic: Allow non-shared device HW interrupts

From: [email-masked] (Eric Auger)
Date: Thu, 18 Jun 2015 19:51:28 +0200

On 06/18/2015 10:37 AM, Marc Zyngier wrote:
> On 17/06/15 16:50, Eric Auger wrote:
>> On 06/17/2015 05:37 PM, Marc Zyngier wrote:
>>> On 17/06/15 16:11, Eric Auger wrote:
>>>> Hi Marc,
>>>> On 06/08/2015 07:04 PM, Marc Zyngier wrote:
>>>>> So far, the only use of the HW interrupt facility is the timer,
>>>>> implying that the active state is context-switched for each vcpu,
>>>>> as the device is is shared across all vcpus.
>>>> s/is//
>>>>>
>>>>> This does not work for a device that has been assigned to a VM,
>>>>> as the guest is entierely in control of that device (the HW is
>>>> entirely?
>>>>> not shared). In that case, it makes sense to bypass the whole
>>>>> active state srtwitchint, and only track the deactivation of the
>>>> switching
>>>
>>> Congratulations, I think you're now ready to try deciphering my
>>> handwriting... ;-)
>> good to see you're not a machine or maybe you do it on purpose some
>> times ;-)
>>>
>>>>> interrupt.
>>>>>
>>>>> Signed-off-by: Marc Zyngier <[email-masked]>
>>>>> ---
>>>>>  include/kvm/arm_vgic.h    |  5 +++--
>>>>>  virt/kvm/arm/arch_timer.c |  2 +-
>>>>>  virt/kvm/arm/vgic.c       | 37 ++++++++++++++++++++++++-------------
>>>>>  3 files changed, 28 insertions(+), 16 deletions(-)
>>>>>
>>>>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>>>>> index 1c653c1..5d47d60 100644
>>>>> --- a/include/kvm/arm_vgic.h
>>>>> +++ b/include/kvm/arm_vgic.h
>>>>> @@ -164,7 +164,8 @@ struct irq_phys_map {
>>>>>  	u32			virt_irq;
>>>>>  	u32			phys_irq;
>>>>>  	u32			irq;
>>>>> -	bool			active;
>>>>> +	bool			shared;
>>>>> +	bool			active; /* Only valid if shared */
>>>>>  };
>>>>>  
>>>>>  struct vgic_dist {
>>>>> @@ -347,7 +348,7 @@ void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg);
>>>>>  int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu);
>>>>>  int kvm_vgic_vcpu_active_irq(struct kvm_vcpu *vcpu);
>>>>>  struct irq_phys_map *vgic_map_phys_irq(struct kvm_vcpu *vcpu,
>>>>> -				       int virt_irq, int irq);
>>>>> +				       int virt_irq, int irq, bool shared);
>>>>>  int vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, struct irq_phys_map *map);
>>>>>  bool vgic_get_phys_irq_active(struct irq_phys_map *map);
>>>>>  void vgic_set_phys_irq_active(struct irq_phys_map *map, bool active);
>>>>> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
>>>>> index b9fff78..9544d79 100644
>>>>> --- a/virt/kvm/arm/arch_timer.c
>>>>> +++ b/virt/kvm/arm/arch_timer.c
>>>>> @@ -202,7 +202,7 @@ void kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
>>>>>  	 * Tell the VGIC that the virtual interrupt is tied to a
>>>>>  	 * physical interrupt. We do that once per VCPU.
>>>>>  	 */
>>>>> -	timer->map = vgic_map_phys_irq(vcpu, irq->irq, host_vtimer_irq);
>>>>> +	timer->map = vgic_map_phys_irq(vcpu, irq->irq, host_vtimer_irq, true);
>>>>>  	WARN_ON(!timer->map);
>>>>>  }
>>>>>  
>>>>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>>>>> index f376b56..4223166 100644
>>>>> --- a/virt/kvm/arm/vgic.c
>>>>> +++ b/virt/kvm/arm/vgic.c
>>>>> @@ -1125,18 +1125,21 @@ static void vgic_queue_irq_to_lr(struct kvm_vcpu *vcpu, int irq,
>>>>>  		map = vgic_irq_map_search(vcpu, irq);
>>>>>  
>>>>>  		if (map) {
>>>>> -			int ret;
>>>>> -
>>>>> -			BUG_ON(!map->active);
>>>>>  			vlr.hwirq = map->phys_irq;
>>>>>  			vlr.state |= LR_HW;
>>>>>  			vlr.state &= ~LR_EOI_INT;
>>>>>  
>>>>> -			ret = irq_set_irqchip_state(map->irq,
>>>>> -						    IRQCHIP_STATE_ACTIVE,
>>>>> -						    true);
>>>>>  			vgic_irq_set_queued(vcpu, irq);
>>>>
>>>> the queued state is set again in vgic_queue_hwirq for level_sensitive
>>>> IRQs although not harmful.
>>>
>>> Indeed. We still need it for edge interrupts though. I'll try to find a
>>> nicer way...
>>>
>>>>> -			WARN_ON(ret);
>>>>> +
>>>>> +			if (map->shared) {
>>>>> +				int ret;
>>>>> +
>>>>> +				BUG_ON(!map->active);
>>>>> +				ret = irq_set_irqchip_state(map->irq,
>>>>> +							    IRQCHIP_STATE_ACTIVE,
>>>>> +							    true);
>>>>> +				WARN_ON(ret);
>>>>> +			}
>>>>>  		}
>>>>>  	}
>>>>>  
>>>>> @@ -1368,21 +1371,28 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>>>>>  static int vgic_sync_hwirq(struct kvm_vcpu *vcpu, struct vgic_lr vlr)
>>>>>  {
>>>>>  	struct irq_phys_map *map;
>>>>> +	bool active;
>>>>>  	int ret;
>>>>>  
>>>>>  	if (!(vlr.state & LR_HW))
>>>>>  		return 0;
>>>>>  
>>>>>  	map = vgic_irq_map_search(vcpu, vlr.irq);
>>>>> -	BUG_ON(!map || !map->active);
>>>>> +	BUG_ON(!map);
>>>>> +	BUG_ON(map->shared && !map->active);
>>>>>  
>>>>>  	ret = irq_get_irqchip_state(map->irq,
>>>>>  				    IRQCHIP_STATE_ACTIVE,
>>>>> -				    &map->active);
>>>>> +				    &active);
>>>>>  
>>>> In case of non shared and EOIMode = 1 - I know this is not your current
>>>> interest here though ;-) - , once the guest EOIs its virtual IRQ and GIC
>>>> deactivates the physical one, a new phys IRQ can hit immediatly, the
>>>> physical handler can be entered and the state is seen as active here.
>>>> The queued state is never reset in such a case and the system gets stuck
>>>> since the can_sample fails I think. What I mean here is sounds the state
>>>> machine as is does not work for my VFIO case. So some adaptations still
>>>> are needed I think. Do you share my diagnosis?
>>>
>>> Yup, there is something that doesn't quite work here.
>>>
>>> I think the mistake is to sample the distributor active state. I wonder
>>> if I can simply rely on the LR state. If it is neither pending nor
>>> active, it means that we have done the deactivation, and we can then
>>> reset the queued state.
>>
>> I tried to use the LR in the past - it was also Christoffer's will - but
>> it was not working. I observed injection before seeing the LR voided.
>> This is why I resorted to using the pending state instead and treated
>> forwarded IRQ as edge in vgic_queue_hwirq.  sampling could be done only
>> if the IRQ was pending.
> 
> Of course, you're right. The LR state is not used at all for a physical
> interrupt (the HW bit really says "use the distributor").
> 
> I've given it more thoughts last night, and I think we can solve this is
> a fairly simple way. In the scenario you outline, we do not observe the
> ACTIVE to INACTIVE transition because the interrupt has fired again,
> leaving the interrupt flagged as queued.
> 
> I think we can clear the "queued" bit on injection, as we're guaranteed
> that seeing a new interrupt is the proof that the previous one has been
> deactivated (how could we see it otherwise?).
> 
> How about the following (untested) patch:

If think in EOIMode =1 it is indeed fairly safe. I will do some testing
and let you know ...

Best Regards

Eric
> 
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 6687ac4..a01f821 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -1387,8 +1387,17 @@ static int vgic_sync_hwirq(struct kvm_vcpu *vcpu,
> struct vgic_lr vlr)
> 
>  	WARN_ON(ret);
> 
> +	/*
> +	 * For a non-shared interrupt, we have to cater for two
> +	 * possible deactivation conditions
> +	 *
> +	 * - the interrupt is now inactive
> +	 * - the interrupt is still active, but is flagged as not
> +	 *   queued, indicating another interrupt has fired before we
> +	 *   could observe the deactivate.
> +	 */
>  	if (!map->shared)
> -		return !active;
> +		return !active || !vgic_irq_is_queued(vcpu, vlr.irq);
> 
>  	map->active = active;
> 
> @@ -1534,6 +1543,7 @@ static int vgic_update_irq_pending(struct kvm
> *kvm, int cpuid,
>  	int edge_triggered, level_triggered;
>  	int enabled;
>  	bool ret = true, can_inject = true;
> +	struct irq_phys_map *map;
> 
>  	spin_lock(&dist->lock);
> 
> @@ -1580,6 +1590,18 @@ static int vgic_update_irq_pending(struct kvm
> *kvm, int cpuid,
>  		goto out;
>  	}
> 
> +	map = vgic_irq_map_search(vcpu, irq_num);
> +	if (map && !map->shared) {
> +		/*
> +		 * We are told to inject a HW irq, so we have to trust
> +		 * the caller that the previous one has been EOIed,
> +		 * and that a new one is now active. Clearing the
> +		 * queued state will have the effect of making it
> +		 * sample-able again.
> +		 */
> +		vgic_irq_clear_queued(vcpu, irq_num);
> +	}
> +
>  	if (!vgic_can_sample_irq(vcpu, irq_num)) {
>  		/*
>  		 * Level interrupt in progress, will be picked up
> 
> Thoughts?
> 
> 	M.
>