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

From: [email-masked] (Marc Zyngier)
Date: Wed, 17 Jun 2015 16:37:41 +0100

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... ;-)

>> 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.

As a bonus, it would save a read from MMIO, which is often dog slow.

Thoughts?

	M.
> 
> Eric
>>  
>> -	if (map->active) {
>> +	if (!map->shared)
>> +		return !active;
>> +
>> +	map->active = active;
>> +
>> +	if (active) {
>>  		ret = irq_set_irqchip_state(map->irq,
>>  					    IRQCHIP_STATE_ACTIVE,
>>  					    false);
>> @@ -1663,7 +1673,7 @@ static struct rb_root *vgic_get_irq_phys_map(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)
>>  {
>>  	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>>  	struct rb_root *root = vgic_get_irq_phys_map(vcpu, virt_irq);
>> @@ -1710,6 +1720,7 @@ struct irq_phys_map *vgic_map_phys_irq(struct kvm_vcpu *vcpu,
>>  	new_map->virt_irq = virt_irq;
>>  	new_map->phys_irq = phys_irq;
>>  	new_map->irq = irq;
>> +	new_map->shared = shared;
>>  
>>  	rb_link_node(&new_map->node, parent, new);
>>  	rb_insert_color(&new_map->node, root);
>> @@ -1746,13 +1757,13 @@ static struct irq_phys_map *vgic_irq_map_search(struct kvm_vcpu *vcpu,
>>  
>>  bool vgic_get_phys_irq_active(struct irq_phys_map *map)
>>  {
>> -	BUG_ON(!map);
>> +	BUG_ON(!map || !map->shared);
>>  	return map->active;
>>  }
>>  
>>  void vgic_set_phys_irq_active(struct irq_phys_map *map, bool active)
>>  {
>> -	BUG_ON(!map);
>> +	BUG_ON(!map || !map->shared);
>>  	map->active = active;
>>  }
>>  
>>
> 

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