diff --git a/xen/include/asm-arm/spinlock.h b/xen/include/asm-arm/spinlock.h
new file mode 100644
index 0000000000..81955d1697
--- /dev/null
+++ b/xen/include/asm-arm/spinlock.h
@@ -0,0 +1,6 @@
+#ifndef __ASM_SPINLOCK_H
+#define __ASM_SPINLOCK_H
+
+/* Nothing ARM specific. */
+
+#endif /* __ASM_SPINLOCK_H */
diff --git a/xen/include/asm-x86/spinlock.h b/xen/include/asm-x86/spinlock.h
new file mode 100644
index 0000000000..7d69e75a93
--- /dev/null
+++ b/xen/include/asm-x86/spinlock.h
@@ -0,0 +1,7 @@
+#ifndef __ASM_SPINLOCK_H
+#define __ASM_SPINLOCK_H
+
+#define _raw_read_unlock(l) \
+    asm volatile ( "lock; dec%z0 %0" : "+m" ((l)->lock) :: "memory" )
+
+#endif /* __ASM_SPINLOCK_H */
diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index 9286543bea..fb0438e542 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -2,6 +2,7 @@
 #define __SPINLOCK_H__
 
 #include <asm/system.h>
+#include <asm/spinlock.h>
 
 #ifndef NDEBUG
 struct lock_debug {