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Date:   Wed, 30 Aug 2017 13:46:46 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
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>,
        Eric Auger <eric.auger@...hat.com>,
        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

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@....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?

Alternatively, can you look it up using
vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq() and another 'ioctl' in
irq_set_vcpu_affinity() somehow instead of looping around and testing?

>  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;
> +	int ret, idx;
>  
>  	dump_routing(virq, irq_entry, true);
>  
> @@ -280,6 +294,11 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
>  	if (ret)
>  		goto out;
>  
> +	idx = vgic_v4_vcpu_to_index(&kvm->arch.vgic.its_vm,
> +				    irq->target_vcpu);
> +	if (idx < 0)
> +		goto out;
> +
>  	/*
>  	 * Emit the mapping request. If it fails, the ITS probably
>  	 * isn't v4 compatible, so let's silently bail out. Holding
> @@ -290,7 +309,7 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
>  		.vm		= &kvm->arch.vgic.its_vm,
>  		.vintid		= irq->intid,
>  		.db_enabled	= true,
> -		.vpe_idx	= irq->target_vcpu->vcpu_id,
> +		.vpe_idx	= idx,
>  	};
>  
>  	if (its_map_vlpi(virq, &map))
> 
> Another option would be to just pass the pointer to the vpe instead,
> and let the irq code to figure out the index, which can easily be
> derived the doorbells (vpe->vpe_db_lpi - vpe->its_vm->db_lpi_base).
> 
> I'll work something out for the next version.

Ah, yeah, so I guess that is an option.

It should be pretty quick to loop over even hundreds of vcpus, but that
kind of thing just always seems wrong, somehow.

Thanks,
-Christoffer

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