[KVM PATCH v3 2/3] KVM: export lockless GSI attribute

[Gregory Haskins <ghaskins@novell.com>]

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      |   35 ++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 1fe135d..01151a6 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 {
@@ -420,6 +421,7 @@ 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 db2553f..a7fd487 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -173,6 +173,35 @@ 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;
+	int idx;
+
+	idx = srcu_read_lock(&kvm->irq_routing.srcu);
+	irq_rt = rcu_dereference(kvm->irq_routing.table);
+	if (irq < irq_rt->nr_rt_entries)
+		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
+			if (!e->lockless) {
+				/*
+				 * all destinations need to be lockless to
+				 * declare that the GSI as a whole is also
+				 * lockless
+				 */
+				ret = 0;
+				break;
+			}
+
+			ret = 1;
+		}
+	srcu_read_unlock(&kvm->irq_routing.srcu, idx);
+
+	return ret;
+}
+
 void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
 {
 	struct kvm_irq_ack_notifier *kian;
@@ -310,18 +339,22 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
 	int delta;
 	struct kvm_kernel_irq_routing_entry *ei;
 	struct hlist_node *n;
+	bool lockless = ue->type == KVM_IRQ_ROUTING_MSI;
 
 	/*
 	 * Do not allow GSI to be mapped to the same irqchip more than once.
 	 * Allow only one to one mapping between GSI and MSI.
+	 * Do not allow mixed lockless vs locked variants to coexist.
 	 */
 	hlist_for_each_entry(ei, n, &rt->map[ue->gsi], link)
 		if (ei->type == KVM_IRQ_ROUTING_MSI ||
-		    ue->u.irqchip.irqchip == ei->irqchip.irqchip)
+		    ue->u.irqchip.irqchip == ei->irqchip.irqchip ||
+		    ei->lockless != lockless)
 			return r;
 
 	e->gsi = ue->gsi;
 	e->type = ue->type;
+	e->lockless = lockless;
 	switch (ue->type) {
 	case KVM_IRQ_ROUTING_IRQCHIP:
 		delta = 0;