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

From: [email-masked] (Marc Zyngier)
Date: Wed, 01 Jul 2015 11:20:45 +0100

On 30/06/15 21:19, Christoffer Dall wrote:
> 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?

Not very easily. There was some work done a while ago for the dentry
cache IIRC, but I doubt that's reusable directly, and probably overkill.

RCU protected lists are, on the other hand, readily available. Bah. I'll
switch to this. By the time it becomes the bottleneck, the world will
have moved on. Or so I hope.

	M.

> 
> Thanks,
> -Christoffer
> 
>>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  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
>>
> 

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