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

[Christoffer Dall <cdall@linaro.org>]

On Wed, Aug 30, 2017 at 01:53:30PM +0100, Marc Zyngier wrote:
> 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...
> 
Yes, indeed.  Looks good to me as well.

The only thing that makes me slightly nervous is the use of target_vcpu,
but I think we rely on it never being NULL for LPIs elsewhere in the
code, so we should be fine.

Thanks,
-Christoffer