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

[Marc Zyngier]

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@xxxxxxx>
>> ---
>>  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,
>> +	};
>> +
>> +	if (its_map_vlpi(virq, &map))
>> +		goto out;
> 
> This seems to be able to return things like -ENOMEM, whould we really
> not report this back to the caller in any way?


That's a good question.

If we return -ENOMEM, we'll probably end-up returning an error to
userspace (as a result of the VFIO ioctl), which will in turn probably
terminate the guest (I'm guessing, I haven't actually looked at what
userspace does).

If we don't return the error, then we have a chance to keep the guest
running by sticking to software injection.

I'm not sure what is preferable...

Thanks,

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