[PATCH 06/10] KVM: arm/arm64: vgic: Allow dynamic mapping of physical/virtual interrupts

[christoffer.dall@linaro.org (Christoffer Dall)]

On Mon, Jun 08, 2015 at 06:04:01PM +0100, Marc Zyngier wrote:
> In order to be able to feed physical interrupts to a guest, we need
> to be able to establish the virtual-physical mapping between the two
> worlds.
> 
> The mapping is kept in a rbtree, indexed by virtual interrupts.

how many of these do you expect there will be?  Is the extra code and
complexity of an rbtree really warranted?

I would assume that you'll have one PPI for each CPU in the default case
plus potentially a few more for an assigned network adapter, let's say a
couple of handfulls.  Am I missing something obvious or is this
optimization of traversing a list of 10-12 mappings in the typical case
not likely to be measurable?

I would actually be more concerned about the additional locking and
would look at RCU for protecting a list instead.  Can you protect an
rbtree with RCU easily?

Thanks,
-Christoffer

> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  include/kvm/arm_vgic.h |  18 ++++++++
>  virt/kvm/arm/vgic.c    | 110 +++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 128 insertions(+)
> 
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 4f9fa1d..33d121a 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -159,6 +159,14 @@ struct vgic_io_device {
>  	struct kvm_io_device dev;
>  };
>  
> +struct irq_phys_map {
> +	struct rb_node		node;
> +	u32			virt_irq;
> +	u32			phys_irq;
> +	u32			irq;
> +	bool			active;
> +};
> +
>  struct vgic_dist {
>  	spinlock_t		lock;
>  	bool			in_kernel;
> @@ -256,6 +264,10 @@ struct vgic_dist {
>  	struct vgic_vm_ops	vm_ops;
>  	struct vgic_io_device	dist_iodev;
>  	struct vgic_io_device	*redist_iodevs;
> +
> +	/* Virtual irq to hwirq mapping */
> +	spinlock_t		irq_phys_map_lock;

why do we need a separate lock here?

> +	struct rb_root		irq_phys_map;
>  };
>  
>  struct vgic_v2_cpu_if {
> @@ -307,6 +319,9 @@ struct vgic_cpu {
>  		struct vgic_v2_cpu_if	vgic_v2;
>  		struct vgic_v3_cpu_if	vgic_v3;
>  	};
> +
> +	/* Protected by the distributor's irq_phys_map_lock */
> +	struct rb_root	irq_phys_map;
>  };
>  
>  #define LR_EMPTY	0xff
> @@ -331,6 +346,9 @@ int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
>  void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg);
>  int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu);
>  int kvm_vgic_vcpu_active_irq(struct kvm_vcpu *vcpu);
> +struct irq_phys_map *vgic_map_phys_irq(struct kvm_vcpu *vcpu,
> +				       int virt_irq, int irq);
> +int vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, struct irq_phys_map *map);
>  
>  #define irqchip_in_kernel(k)	(!!((k)->arch.vgic.in_kernel))
>  #define vgic_initialized(k)	(!!((k)->arch.vgic.nr_cpus))
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 59ed7a3..c6604f2 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -24,6 +24,7 @@
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>  #include <linux/of_irq.h>
> +#include <linux/rbtree.h>
>  #include <linux/uaccess.h>
>  
>  #include <linux/irqchip/arm-gic.h>
> @@ -84,6 +85,8 @@ static void vgic_retire_disabled_irqs(struct kvm_vcpu *vcpu);
>  static void vgic_retire_lr(int lr_nr, int irq, struct kvm_vcpu *vcpu);
>  static struct vgic_lr vgic_get_lr(const struct kvm_vcpu *vcpu, int lr);
>  static void vgic_set_lr(struct kvm_vcpu *vcpu, int lr, struct vgic_lr lr_desc);
> +static struct irq_phys_map *vgic_irq_map_search(struct kvm_vcpu *vcpu,
> +						int virt_irq);
>  
>  static const struct vgic_ops *vgic_ops;
>  static const struct vgic_params *vgic;
> @@ -1585,6 +1588,112 @@ static irqreturn_t vgic_maintenance_handler(int irq, void *data)
>  	return IRQ_HANDLED;
>  }
>  
> +static struct rb_root *vgic_get_irq_phys_map(struct kvm_vcpu *vcpu,
> +					     int virt_irq)
> +{
> +	if (virt_irq < VGIC_NR_PRIVATE_IRQS)
> +		return &vcpu->arch.vgic_cpu.irq_phys_map;
> +	else
> +		return &vcpu->kvm->arch.vgic.irq_phys_map;
> +}
> +
> +struct irq_phys_map *vgic_map_phys_irq(struct kvm_vcpu *vcpu,
> +				       int virt_irq, int irq)
> +{
> +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +	struct rb_root *root = vgic_get_irq_phys_map(vcpu, virt_irq);
> +	struct rb_node **new = &root->rb_node, *parent = NULL;
> +	struct irq_phys_map *new_map;
> +	struct irq_desc *desc;
> +	struct irq_data *data;
> +	int phys_irq;
> +
> +	desc = irq_to_desc(irq);
> +	if (!desc) {
> +		kvm_err("kvm_arch_timer: can't obtain interrupt descriptor\n");
> +		return NULL;
> +	}
> +
> +	data = irq_desc_get_irq_data(desc);
> +	while (data->parent_data)
> +		data = data->parent_data;
> +
> +	phys_irq = data->hwirq;
> +
> +	spin_lock(&dist->irq_phys_map_lock);
> +
> +	/* Boilerplate rb_tree code */
> +	while (*new) {
> +		struct irq_phys_map *this;
> +
> +		this = container_of(*new, struct irq_phys_map, node);
> +		parent = *new;
> +		if (this->virt_irq < virt_irq)
> +			new = &(*new)->rb_left;
> +		else if (this->virt_irq > virt_irq)
> +			new = &(*new)->rb_right;
> +		else {
> +			new_map = this;
> +			goto out;
> +		}
> +	}
> +
> +	new_map = kzalloc(sizeof(*new_map), GFP_KERNEL);
> +	if (!new_map)
> +		goto out;
> +
> +	new_map->virt_irq = virt_irq;
> +	new_map->phys_irq = phys_irq;
> +	new_map->irq = irq;
> +
> +	rb_link_node(&new_map->node, parent, new);
> +	rb_insert_color(&new_map->node, root);
> +
> +out:
> +	spin_unlock(&dist->irq_phys_map_lock);
> +	return new_map;
> +}
> +
> +static struct irq_phys_map *vgic_irq_map_search(struct kvm_vcpu *vcpu,
> +						int virt_irq)
> +{
> +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +	struct rb_root *root = vgic_get_irq_phys_map(vcpu, virt_irq);
> +	struct rb_node *node = root->rb_node;
> +	struct irq_phys_map *this = NULL;
> +
> +	spin_lock(&dist->irq_phys_map_lock);
> +
> +	while (node) {
> +		this = container_of(node, struct irq_phys_map, node);
> +
> +		if (this->virt_irq < virt_irq)
> +			node = node->rb_left;
> +		else if (this->virt_irq > virt_irq)
> +			node = node->rb_right;
> +		else
> +			break;
> +	}
> +
> +	spin_unlock(&dist->irq_phys_map_lock);
> +	return this;
> +}
> +
> +int vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, struct irq_phys_map *map)
> +{
> +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +
> +	if (!map)
> +		return -EINVAL;
> +
> +	spin_lock(&dist->irq_phys_map_lock);
> +	rb_erase(&map->node, vgic_get_irq_phys_map(vcpu, map->virt_irq));
> +	spin_unlock(&dist->irq_phys_map_lock);
> +
> +	kfree(map);
> +	return 0;
> +}
> +
>  void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
>  {
>  	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> @@ -1835,6 +1944,7 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  		goto out_unlock;
>  
>  	spin_lock_init(&kvm->arch.vgic.lock);
> +	spin_lock_init(&kvm->arch.vgic.irq_phys_map_lock);
>  	kvm->arch.vgic.in_kernel = true;
>  	kvm->arch.vgic.vgic_model = type;
>  	kvm->arch.vgic.vctrl_base = vgic->vctrl_base;
> -- 
> 2.1.4
>