[RFC v2 2/9] KVM: ARM: VGIC: add forwarded irq rbtree lock

Christoffer Dall
2014-09-11T03:09:53Z

On Mon, Sep 01, 2014 at 02:52:41PM +0200, Eric Auger wrote:
> add a lock related to the rb tree manipulation. The rb tree can be

Ok, I can't hold myself back any longer. Please begin sentences with a
capital letter. You don't do this in French? :)

> searched in one thread (irqfd handler for instance) and map/unmap
> happen in another.
>
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> ---
> include/kvm/arm_vgic.h | 1 +
> virt/kvm/arm/vgic.c | 46 +++++++++++++++++++++++++++++++++++++---------
> 2 files changed, 38 insertions(+), 9 deletions(-)
>
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 743020f..3da244f 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -177,6 +177,7 @@ struct vgic_dist {
> unsigned long irq_pending_on_cpu;
>
> struct rb_root irq_phys_map;
> + spinlock_t rb_tree_lock;
> #endif
> };
>
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 8ef495b..dbc2a5a 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -1630,9 +1630,15 @@ static struct rb_root *vgic_get_irq_phys_map(struct kvm_vcpu *vcpu,
>
> int vgic_map_phys_irq(struct kvm_vcpu *vcpu, int virt_irq, int phys_irq)
> {
> - struct rb_root *root = vgic_get_irq_phys_map(vcpu, virt_irq);
> - struct rb_node **new = &root->rb_node, *parent = NULL;
> + struct rb_root *root;
> + struct rb_node **new, *parent = NULL;
> struct irq_phys_map *new_map;
> + struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +
> + spin_lock(&dist->rb_tree_lock);
> +
> + root = vgic_get_irq_phys_map(vcpu, virt_irq);
> + new = &root->rb_node;
>
> /* Boilerplate rb_tree code */
> while (*new) {
> @@ -1644,13 +1650,17 @@ int vgic_map_phys_irq(struct kvm_vcpu *vcpu, int virt_irq, int phys_irq)
> new = &(*new)->rb_left;
> else if (this->virt_irq > virt_irq)
> new = &(*new)->rb_right;
> - else
> + else {
> + spin_unlock(&dist->rb_tree_lock);
> return -EEXIST;
> + }

can you initialize a ret variable to -EEXIST in the beginning of this
function, and add an out label above the unlock below, replace this
multi-line statement with a goto out, and set ret = 0 after the while
loop?

> }
>
> new_map = kzalloc(sizeof(*new_map), GFP_KERNEL);
> - if (!new_map)
> + if (!new_map) {
> + spin_unlock(&dist->rb_tree_lock);
> return -ENOMEM;

then this becomes ret = -ENOMEM; goto out;

> + }
>
> new_map->virt_irq = virt_irq;
> new_map->phys_irq = phys_irq;
> @@ -1658,6 +1668,8 @@ int vgic_map_phys_irq(struct kvm_vcpu *vcpu, int virt_irq, int phys_irq)
> rb_link_node(&new_map->node, parent, new);
> rb_insert_color(&new_map->node, root);
>
> + spin_unlock(&dist->rb_tree_lock);
> +

aren't you allocating memory with GFP_KERNEL while holding a spinlock
here?

> return 0;
> }
>
> @@ -1685,24 +1697,39 @@ static struct irq_phys_map *vgic_irq_map_search(struct kvm_vcpu *vcpu,
>
> int vgic_get_phys_irq(struct kvm_vcpu *vcpu, int virt_irq)
> {
> - struct irq_phys_map *map = vgic_irq_map_search(vcpu, virt_irq);
> + struct irq_phys_map *map;
> + struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> + int ret;
> +
> + spin_lock(&dist->rb_tree_lock);
> + map = vgic_irq_map_search(vcpu, virt_irq);
>
> if (map)
> - return map->phys_irq;
> + ret = map->phys_irq;
> + else
> + ret = -ENOENT;

initialize ret to -ENOENT and avoid the else statement.

> +
> + spin_unlock(&dist->rb_tree_lock);
> + return ret;
>
> - return -ENOENT;
> }
>
> int vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, int virt_irq, int phys_irq)
> {
> - struct irq_phys_map *map = vgic_irq_map_search(vcpu, virt_irq);
> + struct irq_phys_map *map;
> + struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +
> + spin_lock(&dist->rb_tree_lock);
> +
> + map = vgic_irq_map_search(vcpu, virt_irq);
>
> if (map && map->phys_irq == phys_irq) {
> rb_erase(&map->node, vgic_get_irq_phys_map(vcpu, virt_irq));
> kfree(map);
> + spin_unlock(&dist->rb_tree_lock);

can kfree sleep? I don't remember. In any case, you can unlock before
calling kfree.

> return 0;
> }
> -
> + spin_unlock(&dist->rb_tree_lock);
> return -ENOENT;

an out label and single unlock location would be preferred here as well
I think.

> }
>
> @@ -1898,6 +1925,7 @@ int kvm_vgic_create(struct kvm *kvm)
> }
>
> spin_lock_init(&kvm->arch.vgic.lock);
> + spin_lock_init(&kvm->arch.vgic.rb_tree_lock);
> kvm->arch.vgic.in_kernel = true;
> kvm->arch.vgic.vctrl_base = vgic->vctrl_base;
> kvm->arch.vgic.vgic_dist_base = VGIC_ADDR_UNDEF;
> --
> 1.9.1
>