diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index e06dd08..5bdae24 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -561,8 +561,10 @@ static void free_dev_irq_entries(AssignedDevice *dev)
 {
     int i;
 
-    for (i = 0; i < dev->irq_entries_nr; i++)
+    for (i = 0; i < dev->irq_entries_nr; i++) {
         kvm_del_routing_entry(kvm_context, &dev->entry[i]);
+        kvm_free_irq_route_gsi(kvm_context, dev->entry[i].gsi);
+    }
     free(dev->entry);
     dev->entry = NULL;
     dev->irq_entries_nr = 0;
diff --git a/kvm/libkvm/kvm-common.h b/kvm/libkvm/kvm-common.h
index 591fb53..4b3cb51 100644
--- a/kvm/libkvm/kvm-common.h
+++ b/kvm/libkvm/kvm-common.h
@@ -66,8 +66,10 @@ struct kvm_context {
 #ifdef KVM_CAP_IRQ_ROUTING
 	struct kvm_irq_routing *irq_routes;
 	int nr_allocated_irq_routes;
+	void *used_gsi_bitmap;
+	int max_gsi;
+	pthread_mutex_t gsi_mutex;
 #endif
-	int max_used_gsi;
 };
 
 int kvm_alloc_kernel_memory(kvm_context_t kvm, unsigned long memory,
diff --git a/kvm/libkvm/libkvm.c b/kvm/libkvm/libkvm.c
index 2a4165a..13a2c21 100644
--- a/kvm/libkvm/libkvm.c
+++ b/kvm/libkvm/libkvm.c
@@ -35,6 +35,7 @@
 #include <errno.h>
 #include <sys/ioctl.h>
 #include <inttypes.h>
+#include <pthread.h>
 #include "libkvm.h"
 
 #if defined(__x86_64__) || defined(__i386__)
@@ -322,6 +323,9 @@ kvm_context_t kvm_init(struct kvm_callbacks *callbacks,
 	kvm->dirty_pages_log_all = 0;
 	kvm->no_irqchip_creation = 0;
 	kvm->no_pit_creation = 0;
+#ifdef KVM_CAP_IRQ_ROUTING
+	pthread_mutex_init(&kvm->gsi_mutex, NULL);
+#endif
 
 	return kvm;
  out_close:
@@ -1298,8 +1302,6 @@ int kvm_add_routing_entry(kvm_context_t kvm,
 	new->flags = entry->flags;
 	new->u = entry->u;
 
-	if (entry->gsi > kvm->max_used_gsi)
-		kvm->max_used_gsi = entry->gsi;
 	return 0;
 #else
 	return -ENOSYS;
@@ -1404,20 +1406,82 @@ int kvm_commit_irq_routes(kvm_context_t kvm)
 #endif
 }
 
+#ifdef KVM_CAP_IRQ_ROUTING
+static inline void set_bit(unsigned int *buf, int bit)
+{
+	buf[bit >> 5] |= (1U << (bit & 0x1f));
+}
+
+static inline void clear_bit(unsigned int *buf, int bit)
+{
+	buf[bit >> 5] &= ~(1U << (bit & 0x1f));
+}
+
+static int kvm_find_free_gsi(kvm_context_t kvm)
+{
+	int i, bit, gsi;
+	unsigned int *buf = kvm->used_gsi_bitmap;
+
+	for (i = 0; i < (kvm->max_gsi >> 5); i++) {
+		if (buf[i] != ~0U)
+			break;
+	}
+
+	if (i == kvm->max_gsi >> 5)
+		return -ENOSPC;
+
+	bit = ffs(~buf[i]);
+	if (!bit)
+		return -EAGAIN;
+
+	gsi = (bit - 1) | (i << 5);
+	set_bit(buf, gsi);
+	return gsi;
+}
+#endif
+
 int kvm_get_irq_route_gsi(kvm_context_t kvm)
 {
 #ifdef KVM_CAP_IRQ_ROUTING
-	if (kvm->max_used_gsi >= KVM_IOAPIC_NUM_PINS)  {
-	    if (kvm->max_used_gsi + 1 < kvm_get_gsi_count(kvm))
-                return kvm->max_used_gsi + 1;
-            else
-                return -ENOSPC;
-        } else
-            return KVM_IOAPIC_NUM_PINS;
+	int gsi;
+
+	pthread_mutex_lock(&kvm->gsi_mutex);
+
+	if (!kvm->max_gsi) {
+		int i;
+
+		/* Round the number of GSIs supported to a 4 byte
+		 * value so we can search it using ints and ffs */
+		i = kvm_get_gsi_count(kvm) & ~0x1f;
+		kvm->used_gsi_bitmap = malloc(i >> 3);
+		if (!kvm->used_gsi_bitmap) {
+			pthread_mutex_unlock(&kvm->gsi_mutex);
+			return -ENOMEM;
+		}
+		memset(kvm->used_gsi_bitmap, 0, i >> 3);
+		kvm->max_gsi = i;
+
+		/* Mark all the IOAPIC pin GSIs as already used */
+		for (i = 0; i <= KVM_IOAPIC_NUM_PINS; i++)
+			set_bit(kvm->used_gsi_bitmap, i);
+	}
+
+	gsi = kvm_find_free_gsi(kvm);
+	pthread_mutex_unlock(&kvm->gsi_mutex);
+	return gsi;
 #else
 	return -ENOSYS;
 #endif
 }
+ 
+void kvm_free_irq_route_gsi(kvm_context_t kvm, int gsi)
+{
+#ifdef KVM_CAP_IRQ_ROUTING
+	pthread_mutex_lock(&kvm->gsi_mutex);
+	clear_bit(kvm->used_gsi_bitmap, gsi);
+	pthread_mutex_unlock(&kvm->gsi_mutex);
+#endif
+}
 
 #ifdef KVM_CAP_DEVICE_MSIX
 int kvm_assign_set_msix_nr(kvm_context_t kvm,
diff --git a/kvm/libkvm/libkvm.h b/kvm/libkvm/libkvm.h
index c23d37b..4e9344c 100644
--- a/kvm/libkvm/libkvm.h
+++ b/kvm/libkvm/libkvm.h
@@ -856,6 +856,16 @@ int kvm_commit_irq_routes(kvm_context_t kvm);
  */
 int kvm_get_irq_route_gsi(kvm_context_t kvm);
 
+/*!
+ * \brief Free used GSI number
+ *
+ * Free used GSI number acquired from kvm_get_irq_route_gsi()
+ *
+ * \param kvm Pointer to the current kvm_context
+ * \param gsi GSI number to free
+ */
+void kvm_free_irq_route_gsi(kvm_context_t kvm, int gsi);
+
 #ifdef KVM_CAP_DEVICE_MSIX
 int kvm_assign_set_msix_nr(kvm_context_t kvm,
 			   struct kvm_assigned_msix_nr *msix_nr);
