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>

drivers/kvm/kvm.h

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);

drivers/kvm/kvm_main.c

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index d395c98..dfb65e2 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -498,6 +498,17 @@
 }
 EXPORT_SYMBOL_GPL(is_error_page);
 
+static inline unsigned long bad_hva(void)
+{
+	return PAGE_OFFSET;
+}
+
+int kvm_is_error_hva(unsigned long addr)
+{
+	return addr == bad_hva();
+}
+EXPORT_SYMBOL_GPL(kvm_is_error_hva);
+
 gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn)
 {
 	int i;