KVM: add kvm_is_error_hva()

Check for the "error hva", an address outside the user address space that
signals a bad gfn.

Signed-off-by: Izik Eidus <izike@qumranet.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 3f5ffc3..6498324 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -520,6 +520,7 @@
 extern struct page *bad_page;
 
 int is_error_page(struct page *page);
+int kvm_is_error_hva(unsigned long addr);
 int kvm_set_memory_region(struct kvm *kvm,
 			  struct kvm_userspace_memory_region *mem,
 			  int user_alloc);