[PATCH 1/2] KVM: Implement default IRQ routing

[Paul Mackerras <paulus@samba.org>]

This implements a simple way to express the case of IRQ routing where
there is one in-kernel PIC and the system interrupts (GSIs) are routed
1-1 to the corresponding pins of the PIC.  This is expressed by having
kvm->irq_routing = NULL with a skeleton irq routing entry in the new
kvm->default_irq_route field.

This provides a convenient way to provide backwards compatibility when
adding IRQ routing capability to an existing in-kernel PIC, such as the
XICS emulation on powerpc.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/eventfd.c       |  4 ++++
 virt/kvm/irqchip.c       | 23 ++++++++++++++++++++---
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 749bdb1..609f587 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -394,6 +394,7 @@ struct kvm {
 	 * if configured, irqfds.lock.
 	 */
 	struct kvm_irq_routing_table __rcu *irq_routing;
+	struct kvm_kernel_irq_routing_entry default_irq_route;
 	struct hlist_head mask_notifier_list;
 	struct hlist_head irq_ack_notifier_list;
 #endif
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index abe4d60..7010cb3 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -272,6 +272,10 @@ static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd,
 {
 	struct kvm_kernel_irq_routing_entry *e;
 
+	if (!irq_rt) {
+		rcu_assign_pointer(irqfd->irq_entry, NULL);
+		return;
+	}
 	if (irqfd->gsi >= irq_rt->nr_rt_entries) {
 		rcu_assign_pointer(irqfd->irq_entry, NULL);
 		return;
diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
index 20dc9e4..ebc2941 100644
--- a/virt/kvm/irqchip.c
+++ b/virt/kvm/irqchip.c
@@ -30,13 +30,24 @@
 #include <trace/events/kvm.h>
 #include "irq.h"
 
+static inline int pin_to_gsi(struct kvm *kvm, unsigned irqchip, unsigned pin)
+{
+	struct kvm_irq_routing_table *rt;
+	int gsi = pin;
+
+	rt = rcu_dereference(kvm->irq_routing);
+	if (rt)
+		gsi = rt->chip[irqchip][pin];
+	return gsi;
+}
+
 bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin)
 {
 	struct kvm_irq_ack_notifier *kian;
 	int gsi;
 
 	rcu_read_lock();
-	gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin];
+	gsi = pin_to_gsi(kvm, irqchip, pin);
 	if (gsi != -1)
 		hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
 					 link)
@@ -59,7 +70,7 @@ void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
 	trace_kvm_ack_irq(irqchip, pin);
 
 	rcu_read_lock();
-	gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin];
+	gsi = pin_to_gsi(kvm, irqchip, pin);
 	if (gsi != -1)
 		hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
 					 link)
@@ -126,7 +137,13 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
 	 */
 	rcu_read_lock();
 	irq_rt = rcu_dereference(kvm->irq_routing);
-	if (irq < irq_rt->nr_rt_entries)
+	if (!irq_rt) {
+		if (kvm->default_irq_route.set) {
+			irq_set[i] = kvm->default_irq_route;
+			irq_set[i].gsi = irq;
+			irq_set[i++].irqchip.pin = irq;
+		}
+	} else if (irq < irq_rt->nr_rt_entries)
 		hlist_for_each_entry(e, &irq_rt->map[irq], link)
 			irq_set[i++] = *e;
 	rcu_read_unlock();
-- 
1.8.4.rc3