1 files changed, 68 insertions, 13 deletions

diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
index 0a98fed550ba..a3bf4f1c0d37 100644
--- a/include/vdso/helpers.h
+++ b/include/vdso/helpers.h
@@ -6,6 +6,13 @@
 
 #include <asm/barrier.h>
 #include <vdso/datapage.h>
+#include <vdso/processor.h>
+#include <vdso/clocksource.h>
+
+static __always_inline bool vdso_is_timens_clock(const struct vdso_clock *vc)
+{
+	return IS_ENABLED(CONFIG_TIME_NS) && vc->clock_mode == VDSO_CLOCKMODE_TIMENS;
+}
 
 static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc)
 {
@@ -18,6 +25,28 @@ static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc)
 	return seq;
 }
 
+/*
+ * Variant of vdso_read_begin() to handle VDSO_CLOCKMODE_TIMENS.
+ *
+ * Time namespace enabled tasks have a special VVAR page installed which has
+ * vc->seq set to 1 and vc->clock_mode set to VDSO_CLOCKMODE_TIMENS. For non
+ * time namespace affected tasks this does not affect performance because if
+ * vc->seq is odd, i.e. a concurrent update is in progress the extra check for
+ * vc->clock_mode is just a few extra instructions while spin waiting for
+ * vc->seq to become even again.
+ */
+static __always_inline bool vdso_read_begin_timens(const struct vdso_clock *vc, u32 *seq)
+{
+	while (unlikely((*seq = READ_ONCE(vc->seq)) & 1)) {
+		if (vdso_is_timens_clock(vc))
+			return true;
+		cpu_relax();
+	}
+	smp_rmb();
+
+	return false;
+}
+
 static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc,
 					   u32 start)
 {
@@ -25,20 +54,50 @@ static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc,
 
 	smp_rmb();
 	seq = READ_ONCE(vc->seq);
-	return seq != start;
+	return unlikely(seq != start);
 }
 
-static __always_inline void vdso_write_begin(struct vdso_time_data *vd)
+static __always_inline void vdso_write_seq_begin(struct vdso_clock *vc)
 {
-	struct vdso_clock *vc = vd->clock_data;
+	/*
+	 * WRITE_ONCE() is required otherwise the compiler can validly tear
+	 * updates to vc->seq and it is possible that the value seen by the
+	 * reader is inconsistent.
+	 */
+	WRITE_ONCE(vc->seq, vc->seq + 1);
+}
 
+static __always_inline void vdso_write_seq_end(struct vdso_clock *vc)
+{
 	/*
 	 * WRITE_ONCE() is required otherwise the compiler can validly tear
-	 * updates to vd[x].seq and it is possible that the value seen by the
+	 * updates to vc->seq and it is possible that the value seen by the
 	 * reader is inconsistent.
 	 */
-	WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1);
-	WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1);
+	WRITE_ONCE(vc->seq, vc->seq + 1);
+}
+
+static __always_inline void vdso_write_begin_clock(struct vdso_clock *vc)
+{
+	vdso_write_seq_begin(vc);
+	/* Ensure the sequence invalidation is visible before data is modified */
+	smp_wmb();
+}
+
+static __always_inline void vdso_write_end_clock(struct vdso_clock *vc)
+{
+	/* Ensure the data update is visible before the sequence is set valid again */
+	smp_wmb();
+	vdso_write_seq_end(vc);
+}
+
+static __always_inline void vdso_write_begin(struct vdso_time_data *vd)
+{
+	struct vdso_clock *vc = vd->clock_data;
+
+	vdso_write_seq_begin(&vc[CS_HRES_COARSE]);
+	vdso_write_seq_begin(&vc[CS_RAW]);
+	/* Ensure the sequence invalidation is visible before data is modified */
 	smp_wmb();
 }
 
@@ -46,14 +105,10 @@ static __always_inline void vdso_write_end(struct vdso_time_data *vd)
 {
 	struct vdso_clock *vc = vd->clock_data;
 
+	/* Ensure the data update is visible before the sequence is set valid again */
 	smp_wmb();
-	/*
-	 * WRITE_ONCE() is required otherwise the compiler can validly tear
-	 * updates to vd[x].seq and it is possible that the value seen by the
-	 * reader is inconsistent.
-	 */
-	WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1);
-	WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1);
+	vdso_write_seq_end(&vc[CS_HRES_COARSE]);
+	vdso_write_seq_end(&vc[CS_RAW]);
 }
 
 #endif /* !__ASSEMBLY__ */