[PATCH v5 3/4] kvm: Create kvm_clear_irq()

[Alex Williamson <alex.williamson@redhat.com>]

This is an alternative to kvm_set_irq(,,,0) which returns the previous
assertion state of the interrupt and does nothing if it isn't changed.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 include/linux/kvm_host.h |    3 ++
 virt/kvm/irq_comm.c      |   78 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a7661c0..6c168f1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -219,6 +219,8 @@ struct kvm_kernel_irq_routing_entry {
 	u32 type;
 	int (*set)(struct kvm_kernel_irq_routing_entry *e,
 		   struct kvm *kvm, int irq_source_id, int level);
+	int (*clear)(struct kvm_kernel_irq_routing_entry *e,
+		     struct kvm *kvm, int irq_source_id);
 	union {
 		struct {
 			unsigned irqchip;
@@ -629,6 +631,7 @@ 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_clear_irq(struct kvm *kvm, int irq_source_id, u32 irq);
 int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
 		int irq_source_id, int level);
 void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index 5afb431..76e8f22 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -68,6 +68,42 @@ static int kvm_set_ioapic_irq(struct kvm_kernel_irq_routing_entry *e,
 	return kvm_ioapic_set_irq(ioapic, e->irqchip.pin, level);
 }
 
+static inline int kvm_clear_irq_line_state(unsigned long *irq_state,
+					    int irq_source_id)
+{
+	return !!test_and_clear_bit(irq_source_id, irq_state);
+}
+
+static int kvm_clear_pic_irq(struct kvm_kernel_irq_routing_entry *e,
+			     struct kvm *kvm, int irq_source_id)
+{
+#ifdef CONFIG_X86
+	struct kvm_pic *pic = pic_irqchip(kvm);
+	int level = kvm_clear_irq_line_state(&pic->irq_states[e->irqchip.pin],
+					     irq_source_id);
+	if (level)
+		kvm_pic_set_irq(pic, e->irqchip.pin,
+				!!pic->irq_states[e->irqchip.pin]);
+	return level;
+#else
+	return -1;
+#endif
+}
+
+static int kvm_clear_ioapic_irq(struct kvm_kernel_irq_routing_entry *e,
+				struct kvm *kvm, int irq_source_id)
+{
+	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
+	int level;
+
+	level = kvm_clear_irq_line_state(&ioapic->irq_states[e->irqchip.pin],
+					 irq_source_id);
+	if (level)
+		kvm_ioapic_set_irq(ioapic, e->irqchip.pin,
+				   !!ioapic->irq_states[e->irqchip.pin]);
+	return level;
+}
+
 inline static bool kvm_is_dm_lowest_prio(struct kvm_lapic_irq *irq)
 {
 #ifdef CONFIG_IA64
@@ -190,6 +226,45 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)
 	return ret;
 }
 
+/*
+ * Return value:
+ *  < 0   Error
+ *  = 0   Interrupt was not set, did nothing
+ *  > 0   Interrupt was pending, cleared
+ */
+int kvm_clear_irq(struct kvm *kvm, int irq_source_id, u32 irq)
+{
+	struct kvm_kernel_irq_routing_entry *e, irq_set[KVM_NR_IRQCHIPS];
+	int ret = -EINVAL, i = 0;
+	struct kvm_irq_routing_table *irq_rt;
+	struct hlist_node *n;
+
+	/* Not possible to detect if the guest uses the PIC or the
+	 * IOAPIC.  So clear the bit in both. The guest will ignore
+	 * writes to the unused one.
+	 */
+	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)
+			irq_set[i++] = *e;
+	rcu_read_unlock();
+
+	while (i--) {
+		int r = -EINVAL;
+
+		if (irq_set[i].clear)
+			r = irq_set[i].clear(&irq_set[i], kvm, irq_source_id);
+
+		if (r < 0)
+			continue;
+
+		ret = r + ((ret < 0) ? 0 : ret);
+	}
+
+	return ret;
+}
+
 void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
 {
 	struct kvm_irq_ack_notifier *kian;
@@ -344,16 +419,19 @@ static int setup_routing_entry(struct kvm_irq_routing_table *rt,
 		switch (ue->u.irqchip.irqchip) {
 		case KVM_IRQCHIP_PIC_MASTER:
 			e->set = kvm_set_pic_irq;
+			e->clear = kvm_clear_pic_irq;
 			max_pin = 16;
 			break;
 		case KVM_IRQCHIP_PIC_SLAVE:
 			e->set = kvm_set_pic_irq;
+			e->clear = kvm_clear_pic_irq;
 			max_pin = 16;
 			delta = 8;
 			break;
 		case KVM_IRQCHIP_IOAPIC:
 			max_pin = KVM_IOAPIC_NUM_PINS;
 			e->set = kvm_set_ioapic_irq;
+			e->clear = kvm_clear_ioapic_irq;
 			break;
 		default:
 			goto out;