Re: [KVM PATCH v2 1/2] KVM: export lockless GSI attribute

[Gregory Haskins <gregory.haskins@gmail.com>]

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Gregory Haskins wrote:
> Certain GSI's support lockless injecton, but we have no way to detect
> which ones at the GSI level.  Knowledge of this attribute will be
> useful later in the series so that we can optimize irqfd injection
> paths for cases where we know the code will not sleep.  Therefore,
> we provide an API to query a specific GSI.
> 
> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> ---
> 
>  include/linux/kvm_host.h |    2 ++
>  virt/kvm/irq_comm.c      |   19 +++++++++++++++++++
>  2 files changed, 21 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index bd5a616..93393a4 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -119,6 +119,7 @@ struct kvm_memory_slot {
>  struct kvm_kernel_irq_routing_entry {
>  	u32 gsi;
>  	u32 type;
> +	bool lockless;
>  	int (*set)(struct kvm_kernel_irq_routing_entry *e,
>  		   struct kvm *kvm, int irq_source_id, int level);
>  	union {
> @@ -417,6 +418,7 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
>  				   unsigned long *deliver_bitmask);
>  #endif
>  int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
> +int kvm_irq_check_lockless(struct kvm *kvm, u32 irq);
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
>  void kvm_register_irq_ack_notifier(struct kvm *kvm,
>  				   struct kvm_irq_ack_notifier *kian);
> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> index 00c68d2..04f0134 100644
> --- a/virt/kvm/irq_comm.c
> +++ b/virt/kvm/irq_comm.c
> @@ -174,6 +174,23 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)
>  	return ret;
>  }
>  
> +int kvm_irq_check_lockless(struct kvm *kvm, u32 irq)
> +{
> +	struct kvm_kernel_irq_routing_entry *e;
> +	struct kvm_irq_routing_table *irq_rt;
> +	struct hlist_node *n;
> +	int ret = -ENOENT;
> +
> +	rcu_read_lock();
> +	irq_rt = rcu_dereference(kvm->irq_routing);
> +	if (irq < irq_rt->nr_rt_entries)
> +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> +			ret = e->lockless ? 1 : 0;

Sigh...  just noticed this as it hits the list.  I should probably break
out of the loop here.

> +	rcu_read_unlock();
> +
> +	return ret;
> +}
> +
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
>  {
>  	struct kvm_irq_ack_notifier *kian;
> @@ -314,6 +331,7 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
>  
>  	e->gsi = ue->gsi;
>  	e->type = ue->type;
> +	e->lockless = false;
>  	switch (ue->type) {
>  	case KVM_IRQ_ROUTING_IRQCHIP:
>  		delta = 0;
> @@ -342,6 +360,7 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
>  		e->msi.address_lo = ue->u.msi.address_lo;
>  		e->msi.address_hi = ue->u.msi.address_hi;
>  		e->msi.data = ue->u.msi.data;
> +		e->lockless = true;
>  		break;
>  	default:
>  		goto out;
> 
> --
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