KVM: Userspace controlled irq routing

Currently KVM has a static routing from GSI numbers to interrupts (namely,
0-15 are mapped 1:1 to both PIC and IOAPIC, and 16:23 are mapped 1:1 to
the IOAPIC).  This is insufficient for several reasons:

- HPET requires non 1:1 mapping for the timer interrupt
- MSIs need a new method to assign interrupt numbers and dispatch them
- ACPI APIC mode needs to be able to reassign the PCI LINK interrupts to the
  ioapics

This patch implements an interrupt routing table (as a linked list, but this
can be easily changed) and a userspace interface to replace the table.  The
routing table is initialized according to the current hardwired mapping.

Signed-off-by: Avi Kivity <avi@redhat.com>

include/linux/kvm.h

@@ -398,6 +398,38 @@ struct kvm_trace_rec {
 #endif
 #if defined(CONFIG_X86)
 #define KVM_CAP_REINJECT_CONTROL 24
+#endif
+#if defined(CONFIG_X86)||defined(CONFIG_IA64)
+#define KVM_CAP_IRQ_ROUTING 25
+#endif
+
+#ifdef KVM_CAP_IRQ_ROUTING
+
+struct kvm_irq_routing_irqchip {
+	__u32 irqchip;
+	__u32 pin;
+};
+
+/* gsi routing entry types */
+#define KVM_IRQ_ROUTING_IRQCHIP 1
+
+struct kvm_irq_routing_entry {
+	__u32 gsi;
+	__u32 type;
+	__u32 flags;
+	__u32 pad;
+	union {
+		struct kvm_irq_routing_irqchip irqchip;
+		__u32 pad[8];
+	} u;
+};
+
+struct kvm_irq_routing {
+	__u32 nr;
+	__u32 flags;
+	struct kvm_irq_routing_entry entries[0];
+};
+
 #endif
 
 /*
@@ -430,6 +462,7 @@ struct kvm_trace_rec {
 			_IOW(KVMIO,  0x68, struct kvm_coalesced_mmio_zone)
 #define KVM_ASSIGN_PCI_DEVICE _IOR(KVMIO, 0x69, \
 				   struct kvm_assigned_pci_dev)
+#define KVM_SET_GSI_ROUTING       _IOW(KVMIO, 0x6a, struct kvm_irq_routing)
 #define KVM_ASSIGN_IRQ _IOR(KVMIO, 0x70, \
 			    struct kvm_assigned_irq)
 #define KVM_REINJECT_CONTROL      _IO(KVMIO, 0x71)