[RFC PATCH 2/4] selftests/rseq: Add sched_state rseq field and getter

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Extend struct rseq in the rseq selftests to include the sched_state
field. Implement a getter function for this field.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 tools/testing/selftests/rseq/rseq-abi.h | 17 +++++++++++++++++
 tools/testing/selftests/rseq/rseq.h     |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/tools/testing/selftests/rseq/rseq-abi.h b/tools/testing/selftests/rseq/rseq-abi.h
index fb4ec8a75dd4..15ec333e9eec 100644
--- a/tools/testing/selftests/rseq/rseq-abi.h
+++ b/tools/testing/selftests/rseq/rseq-abi.h
@@ -37,6 +37,13 @@ enum rseq_abi_cs_flags {
 		(1U << RSEQ_ABI_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT),
 };
 
+enum rseq_sched_state {
+	/*
+	 * Task is currently running on a CPU if bit is set.
+	 */
+	RSEQ_SCHED_STATE_ON_CPU		= (1U << 0),
+};
+
 /*
  * struct rseq_abi_cs is aligned on 4 * 8 bytes to ensure it is always
  * contained within a single cache-line. It is usually declared as
@@ -164,6 +171,16 @@ struct rseq_abi {
 	 */
 	__u32 mm_cid;
 
+	/*
+	 * Restartable sequences sched_state field. Updated by the kernel. Read
+	 * by user-space with single-copy atomicity semantics. This fields can
+	 * be read by any userspace thread. Aligned on 32-bit. Contains a
+	 * bitmask of enum rseq_sched_state. This field is provided as a hint
+	 * by the scheduler, and requires that the page holding struct rseq is
+	 * faulted-in for the state update to be performed by the scheduler.
+	 */
+	__u32 sched_state;
+
 	/*
 	 * Flexible array member at end of structure, after last feature field.
 	 */
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index d7364ea4d201..348e9385cb2b 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -236,6 +236,11 @@ static inline void rseq_prepare_unload(void)
 	rseq_clear_rseq_cs();
 }
 
+static inline uint32_t rseq_current_sched_state(void)
+{
+	return RSEQ_ACCESS_ONCE(rseq_get_abi()->sched_state);
+}
+
 static inline __attribute__((always_inline))
 int rseq_cmpeqv_storev(enum rseq_mo rseq_mo, enum rseq_percpu_mode percpu_mode,
 		       intptr_t *v, intptr_t expect,
-- 
2.25.1