1 files changed, 56 insertions, 0 deletions
diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
new file mode 100644
index 0000000000..9a2af9fca4
--- /dev/null
+++ b/include/vdso/helpers.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_HELPERS_H
+#define __VDSO_HELPERS_H
+
+#ifndef __ASSEMBLY__
+
+#include <vdso/datapage.h>
+
+static __always_inline u32 vdso_read_begin(const struct vdso_data *vd)
+{
+	u32 seq;
+
+	while (unlikely((seq = READ_ONCE(vd->seq)) & 1))
+		cpu_relax();
+
+	smp_rmb();
+	return seq;
+}
+
+static __always_inline u32 vdso_read_retry(const struct vdso_data *vd,
+					   u32 start)
+{
+	u32 seq;
+
+	smp_rmb();
+	seq = READ_ONCE(vd->seq);
+	return seq != start;
+}
+
+static __always_inline void vdso_write_begin(struct vdso_data *vd)
+{
+	/*
+	 * WRITE_ONCE it is required otherwise the compiler can validly tear
+	 * updates to vd[x].seq and it is possible that the value seen by the
+	 * reader it is inconsistent.
+	 */
+	WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
+	WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
+	smp_wmb();
+}
+
+static __always_inline void vdso_write_end(struct vdso_data *vd)
+{
+	smp_wmb();
+	/*
+	 * WRITE_ONCE it is required otherwise the compiler can validly tear
+	 * updates to vd[x].seq and it is possible that the value seen by the
+	 * reader it is inconsistent.
+	 */
+	WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
+	WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __VDSO_HELPERS_H */