KVM: Accelerated apic support

This adds a mechanism for exposing the virtual apic tpr to the guest, and a
protocol for letting the guest update the tpr without causing a vmexit if
conditions allow (e.g. there is no interrupt pending with a higher priority
than the new tpr).

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

include/linux/kvm_para.h

@@ -12,6 +12,8 @@
 /* Return values for hypercalls */
 #define KVM_ENOSYS		1000
 
+#define KVM_HC_VAPIC_POLL_IRQ            1
+
 #ifdef __KERNEL__
 /*
  * hypercalls use architecture specific