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Date:   Wed, 30 Aug 2017 12:20:53 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <cdall@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v3 41/59] KVM: arm/arm64: GICv4: Wire mapping/unmapping of
 VLPIs in VFIO irq bypass

Hi Marc,

On 30/08/2017 11:42, 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@....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,
>>> +	};
>>> +
>>> +	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 have not read the whole stuff yet but userspace is not aware of this
negotiation. Everything happens under the hood in kernel, see
virt/lib/irqbypass.c __connect(): if add_producer() fails
prod->del_consumer() is called and we should return to the not optimized
injection.

Thanks

Eric
> 
> I'm not sure what is preferable...
> 
> Thanks,
> 
> 	M.
> 

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