1 files changed, 22 insertions, 0 deletions

diff --git a/arch/arm/include/asm/xen/events.h b/arch/arm/include/asm/xen/events.h
index 94b4e9020b02..5c27696de14f 100644
--- a/arch/arm/include/asm/xen/events.h
+++ b/arch/arm/include/asm/xen/events.h
@@ -15,4 +15,26 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
         return raw_irqs_disabled_flags(regs->ARM_cpsr);
 }
 
+/*
+ * We cannot use xchg because it does not support 8-byte
+ * values. However it is safe to use {ldr,dtd}exd directly because all
+ * platforms which Xen can run on support those instructions.
+ */
+static inline xen_ulong_t xchg_xen_ulong(xen_ulong_t *ptr, xen_ulong_t val)
+{
+        xen_ulong_t oldval;
+        unsigned int tmp;
+
+        wmb();
+        asm volatile("@ xchg_xen_ulong\n"
+                "1:     ldrexd  %0, %H0, [%3]\n"
+                "       strexd  %1, %2, %H2, [%3]\n"
+                "       teq     %1, #0\n"
+                "       bne     1b"
+                : "=&r" (oldval), "=&r" (tmp)
+                : "r" (val), "r" (ptr)
+                : "memory", "cc");
+        return oldval;
+}
+
 #endif /* _ASM_ARM_XEN_EVENTS_H */