KVM: Check for pending events before attempting injection

Instead of blindly attempting to inject an event before each guest entry,
check for a possible event first in vcpu->requests.  Sites that can trigger
event injection are modified to set KVM_REQ_EVENT:

- interrupt, nmi window opening
- ppr updates
- i8259 output changes
- local apic irr changes
- rflags updates
- gif flag set
- event set on exit

This improves non-injecting entry performance, and sets the stage for
non-atomic injection.

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

arch/x86/kvm/i8259.c

@@ -67,6 +67,7 @@ static void pic_unlock(struct kvm_pic *s)
 		if (!found)
 			return;
 
+		kvm_make_request(KVM_REQ_EVENT, found);
 		kvm_vcpu_kick(found);
 	}
 }