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

From: [email-masked] (Marc Zyngier)
Date: Thu, 18 Jun 2015 09:37:23 +0100

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:

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