Re: [PATCH v3 41/59] KVM: arm/arm64: GICv4: Wire mapping/unmapping of VLPIs in VFIO irq bypass

[Marc Zyngier <marc.zyngier@arm.com>]

On 30/08/17 12:46, Christoffer Dall wrote:
> On Wed, Aug 30, 2017 at 11:28:08AM +0100, Marc Zyngier wrote:
>> On 26/08/17 20:48, Christoffer Dall wrote:
>>> On Mon, Jul 31, 2017 at 06:26:19PM +0100, Marc Zyngier wrote:
>>>> Let's use the irq bypass mechanism introduced for platform device
>>>> interrupts to intercept the virtual PCIe endpoint configuration
>>>> and establish our LPI->VLPI mapping.
>>>>
>>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>>> ---
>>>>  include/kvm/arm_vgic.h      |   8 ++++
>>>>  virt/kvm/arm/arm.c          |  27 ++++++++----
>>>>  virt/kvm/arm/vgic/vgic-v4.c | 103 ++++++++++++++++++++++++++++++++++++++++++++
>>>>  3 files changed, 130 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>>>> index 359eeffe9857..050f78d4fb42 100644
>>>> --- a/include/kvm/arm_vgic.h
>>>> +++ b/include/kvm/arm_vgic.h
>>>> @@ -367,4 +367,12 @@ int kvm_vgic_set_forwarding(struct kvm *kvm, unsigned int host_irq,
>>>>  void kvm_vgic_unset_forwarding(struct kvm *kvm, unsigned int host_irq,
>>>>  			       unsigned int vintid);
>>>>  
>>>> +struct kvm_kernel_irq_routing_entry;
>>>> +
>>>> +int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int irq,
>>>> +			       struct kvm_kernel_irq_routing_entry *irq_entry);
>>>> +
>>>> +int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq,
>>>> +				 struct kvm_kernel_irq_routing_entry *irq_entry);
>>>> +
>>>>  #endif /* __KVM_ARM_VGIC_H */
>>>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>>>> index ebab6c29e3be..6803ea27c47d 100644
>>>> --- a/virt/kvm/arm/arm.c
>>>> +++ b/virt/kvm/arm/arm.c
>>>> @@ -1457,11 +1457,16 @@ int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,
>>>>  	struct kvm_kernel_irqfd *irqfd =
>>>>  		container_of(cons, struct kvm_kernel_irqfd, consumer);
>>>>  
>>>> -	if (prod->type != IRQ_BYPASS_VFIO_PLATFORM)
>>>> +	switch (prod->type) {
>>>> +	case IRQ_BYPASS_VFIO_PLATFORM:
>>>> +		return kvm_vgic_set_forwarding(irqfd->kvm, prod->irq,
>>>> +					       irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>>> +	case IRQ_BYPASS_VFIO_PCI_MSI:
>>>> +		return kvm_vgic_v4_set_forwarding(irqfd->kvm, prod->irq,
>>>> +						  &irqfd->irq_entry);
>>>> +	default:
>>>>  		return 0;
>>>> -
>>>> -	return kvm_vgic_set_forwarding(irqfd->kvm, prod->irq,
>>>> -				       irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>>> +	}
>>>>  }
>>>>  void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
>>>>  				      struct irq_bypass_producer *prod)
>>>> @@ -1469,11 +1474,17 @@ void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
>>>>  	struct kvm_kernel_irqfd *irqfd =
>>>>  		container_of(cons, struct kvm_kernel_irqfd, consumer);
>>>>  
>>>> -	if (prod->type != IRQ_BYPASS_VFIO_PLATFORM)
>>>> -		return;
>>>> +	switch (prod->type) {
>>>> +	case IRQ_BYPASS_VFIO_PLATFORM:
>>>> +		kvm_vgic_unset_forwarding(irqfd->kvm, prod->irq,
>>>> +					  irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>>> +		break;
>>>>  
>>>> -	kvm_vgic_unset_forwarding(irqfd->kvm, prod->irq,
>>>> -				  irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>>> +	case IRQ_BYPASS_VFIO_PCI_MSI:
>>>> +		kvm_vgic_v4_unset_forwarding(irqfd->kvm, prod->irq,
>>>> +					     &irqfd->irq_entry);
>>>> +		break;
>>>> +	}
>>>>  }
>>>>  
>>>>  void kvm_arch_irq_bypass_stop(struct irq_bypass_consumer *cons)
>>>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
>>>> index 207e1fda0dcd..338c86c5159f 100644
>>>> --- a/virt/kvm/arm/vgic/vgic-v4.c
>>>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
>>>> @@ -72,3 +72,106 @@ void vgic_v4_teardown(struct kvm *kvm)
>>>>  	its_vm->nr_vpes = 0;
>>>>  	its_vm->vpes = NULL;
>>>>  }
>>>> +
>>>> +static struct vgic_its *vgic_get_its(struct kvm *kvm,
>>>> +				     struct kvm_kernel_irq_routing_entry *irq_entry)
>>>> +{
>>>> +	struct kvm_msi msi  = (struct kvm_msi) {
>>>> +		.address_lo	= irq_entry->msi.address_lo,
>>>> +		.address_hi	= irq_entry->msi.address_hi,
>>>> +		.data		= irq_entry->msi.data,
>>>> +		.flags		= irq_entry->msi.flags,
>>>> +		.devid		= irq_entry->msi.devid,
>>>> +	};
>>>> +
>>>> +	/*
>>>> +	 * Get a reference on the LPI. If NULL, this is not a valid
>>>> +	 * translation for any of our vITSs.
>>>> +	 */
>>>> +	return vgic_msi_to_its(kvm, &msi);
>>>> +}
>>>> +
>>>> +int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
>>>> +			       struct kvm_kernel_irq_routing_entry *irq_entry)
>>>> +{
>>>> +	struct vgic_its *its;
>>>> +	struct vgic_irq *irq;
>>>> +	struct its_vlpi_map map;
>>>> +	int ret;
>>>> +
>>>> +	if (!vgic_is_v4_capable(kvm))
>>>> +		return 0;
>>>> +
>>>> +	/*
>>>> +	 * Get the ITS, and escape early on error (not a valid
>>>> +	 * doorbell for any of our vITSs).
>>>> +	 */
>>>> +	its = vgic_get_its(kvm, irq_entry);
>>>> +	if (IS_ERR(its))
>>>> +		return 0;
>>>> +
>>>> +	mutex_lock(&its->its_lock);
>>>> +
>>>> +	/* Perform then actual DevID/EventID -> LPI translation. */
>>>> +	ret = vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,
>>>> +				   irq_entry->msi.data, &irq);
>>>> +	if (ret)
>>>> +		goto out;
>>>> +
>>>> +	/*
>>>> +	 * Emit the mapping request. If it fails, the ITS probably
>>>> +	 * isn't v4 compatible, so let's silently bail out. Holding
>>>> +	 * the ITS lock should ensure that nothing can modify the
>>>> +	 * target vcpu.
>>>> +	 */
>>>> +	map = (struct its_vlpi_map) {
>>>> +		.vm		= &kvm->arch.vgic.its_vm,
>>>> +		.vintid		= irq->intid,
>>>> +		.db_enabled	= true,
>>>> +		.vpe_idx	= irq->target_vcpu->vcpu_id,
>>
>> This is just wrong. We cannot assume that the vcpu_id has anything to do
>> with the vpe_idx. It happens to be the same thing now, but the two things
>> should be clearly disconnected.
>>
>> I suggest the following (untested):
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
>> index cf5d6e2de6b8..0146e004401a 100644
>> --- a/virt/kvm/arm/vgic/vgic-v4.c
>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
>> @@ -251,13 +251,27 @@ static void dump_routing(int virq, struct kvm_kernel_irq_routing_entry *irq_entr
>>  
>>  }
>>  
>> +static int vgic_v4_vcpu_to_index(struct its_vm *its_vm, struct kvm_vcpu *vcpu)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < its_vm->nr_vpes; i++) {
>> +		struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
>> +
>> +		if (its_vm->vpes[i] == vpe)
>> +			return i;
>> +	}
>> +
>> +	return -ENODEV;
>> +}
>> +
> 
> Stupid question: Can we change the struct its_vlpi_map to contain a
> vpe pointer or in stead of or in addition to the index?

This is obviously the right solution, because the *index* of the VPE 
doesn't really matter for a map/unmap (it only matters for doorbell 
operations, and that's a very different code path).

I came up with the following (untested, again), which is much more
appealing:

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index b47097a3e4b4..0607541fcafc 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -900,7 +900,7 @@ static void its_send_vmapti(struct its_device *dev, u32 id)
 	struct its_vlpi_map *map = &dev->event_map.vlpi_maps[id];
 	struct its_cmd_desc desc;
 
-	desc.its_vmapti_cmd.vpe = map->vm->vpes[map->vpe_idx];
+	desc.its_vmapti_cmd.vpe = map->vpe;
 	desc.its_vmapti_cmd.dev = dev;
 	desc.its_vmapti_cmd.virt_id = map->vintid;
 	desc.its_vmapti_cmd.event_id = id;
@@ -914,7 +914,7 @@ static void its_send_vmovi(struct its_device *dev, u32 id)
 	struct its_vlpi_map *map = &dev->event_map.vlpi_maps[id];
 	struct its_cmd_desc desc;
 
-	desc.its_vmovi_cmd.vpe = map->vm->vpes[map->vpe_idx];
+	desc.its_vmovi_cmd.vpe = map->vpe;
 	desc.its_vmovi_cmd.dev = dev;
 	desc.its_vmovi_cmd.event_id = id;
 	desc.its_vmovi_cmd.db_enabled = map->db_enabled;
diff --git a/include/linux/irqchip/arm-gic-v4.h b/include/linux/irqchip/arm-gic-v4.h
index 52661b838821..58a4d89aa82c 100644
--- a/include/linux/irqchip/arm-gic-v4.h
+++ b/include/linux/irqchip/arm-gic-v4.h
@@ -62,15 +62,15 @@ struct its_vpe {
  * irq_set_vcpu_affinity().
  *
  * @vm:		Pointer to the GICv4 notion of a VM
+ * @vpe:	Pointer to the GICv4 notion of a virtual CPU (VPE)
  * @vintid:	Virtual LPI number
  * @db_enabled:	Is the VPE doorbell to be generated?
- * @vpe_idx:	Index (0-based) of the VPE in this VM. Not the vpe_id!
  */
 struct its_vlpi_map {
 	struct its_vm		*vm;
+	struct its_vpe		*vpe;
 	u32			vintid;
 	bool			db_enabled;
-	u16			vpe_idx;
 };
 
 enum its_vcpu_info_cmd_type {
diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index d790d0c74b8b..6ba3d73e0f70 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -715,7 +715,7 @@ static int vgic_its_cmd_handle_movi(struct kvm *kvm, struct vgic_its *its,
 		if (ret)
 			return ret;
 
-		map.vpe_idx = vcpu->vcpu_id;
+		map.vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
 
 		return its_map_vlpi(ite->irq->host_irq, &map);
 	}
@@ -1184,7 +1184,7 @@ static int vgic_its_cmd_handle_movall(struct kvm *kvm, struct vgic_its *its,
 			struct its_vlpi_map map;
 
 			if (!its_get_vlpi(irq->host_irq, &map)) {
-				map.vpe_idx = vcpu2->vcpu_id;
+				map.vpe = &vcpu2->arch.vgic_cpu.vgic_v3.its_vpe;
 				its_map_vlpi(irq->host_irq, &map);
 			}
 		}
diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
index cf5d6e2de6b8..6ece88322013 100644
--- a/virt/kvm/arm/vgic/vgic-v4.c
+++ b/virt/kvm/arm/vgic/vgic-v4.c
@@ -288,9 +288,9 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
 	 */
 	map = (struct its_vlpi_map) {
 		.vm		= &kvm->arch.vgic.its_vm,
+		.vpe		= &irq->target_vcpu->arch.vgic_cpu.vgic_v3.its_vpe,
 		.vintid		= irq->intid,
 		.db_enabled	= true,
-		.vpe_idx	= irq->target_vcpu->vcpu_id,
 	};
 
 	if (its_map_vlpi(virq, &map))

Maybe I'll introduce a vcpu_to_vpe() helper, but it already looks much 
better to me...

Thanks,

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