1 files changed, 62 insertions, 0 deletions
diff --git a/include/linux/processor.h b/include/linux/processor.h
new file mode 100644
index 000000000..dc78bdc70
--- /dev/null
+++ b/include/linux/processor.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Misc low level processor primitives */
+#ifndef _LINUX_PROCESSOR_H
+#define _LINUX_PROCESSOR_H
+
+#include <asm/processor.h>
+
+/*
+ * spin_begin is used before beginning a busy-wait loop, and must be paired
+ * with spin_end when the loop is exited. spin_cpu_relax must be called
+ * within the loop.
+ *
+ * The loop body should be as small and fast as possible, on the order of
+ * tens of instructions/cycles as a guide. It should and avoid calling
+ * cpu_relax, or any "spin" or sleep type of primitive including nested uses
+ * of these primitives. It should not lock or take any other resource.
+ * Violations of these guidelies will not cause a bug, but may cause sub
+ * optimal performance.
+ *
+ * These loops are optimized to be used where wait times are expected to be
+ * less than the cost of a context switch (and associated overhead).
+ *
+ * Detection of resource owner and decision to spin or sleep or guest-yield
+ * (e.g., spin lock holder vcpu preempted, or mutex owner not on CPU) can be
+ * tested within the loop body.
+ */
+#ifndef spin_begin
+#define spin_begin()
+#endif
+
+#ifndef spin_cpu_relax
+#define spin_cpu_relax() cpu_relax()
+#endif
+
+#ifndef spin_end
+#define spin_end()
+#endif
+
+/*
+ * spin_until_cond can be used to wait for a condition to become true. It
+ * may be expected that the first iteration will true in the common case
+ * (no spinning), so that callers should not require a first "likely" test
+ * for the uncontended case before using this primitive.
+ *
+ * Usage and implementation guidelines are the same as for the spin_begin
+ * primitives, above.
+ */
+#ifndef spin_until_cond
+#define spin_until_cond(cond)					\
+do {								\
+	if (unlikely(!(cond))) {				\
+		spin_begin();					\
+		do {						\
+			spin_cpu_relax();			\
+		} while (!(cond));				\
+		spin_end();					\
+	}							\
+} while (0)
+
+#endif
+
+#endif /* _LINUX_PROCESSOR_H */