KVM: introduce KVM_HVA_ERR_RO_BAD

In the later patch, it indicates failure when we try to get a writable
hva from the readonly memslot
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>

include/linux/kvm_host.h

@@ -82,11 +82,12 @@ static inline bool is_invalid_pfn(pfn_t pfn)
 	return !is_noslot_pfn(pfn) && is_error_pfn(pfn);
 }
 
-#define KVM_HVA_ERR_BAD	(PAGE_OFFSET)
+#define KVM_HVA_ERR_BAD		(PAGE_OFFSET)
+#define KVM_HVA_ERR_RO_BAD	(PAGE_OFFSET + PAGE_SIZE)
 
 static inline bool kvm_is_error_hva(unsigned long addr)
 {
-	return addr == PAGE_OFFSET;
+	return addr >= PAGE_OFFSET;
 }
 
 #define KVM_ERR_PTR_BAD_PAGE	(ERR_PTR(-ENOENT))