linux-kernel - [RFC PATCH 2/4] selftests/rseq: Add sched

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Message-Id: <20230517152654.7193-3-mathieu.desnoyers@efficios.com>
Date:   Wed, 17 May 2023 11:26:52 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org, Christian Brauner <brauner@...nel.org>,
        Florian Weimer <fw@...eb.enyo.de>, David.Laight@...LAB.COM,
        carlos@...hat.com, Peter Oskolkov <posk@...k.io>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        Chris Kennelly <ckennelly@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        André Almeida <andrealmeid@...lia.com>,
        libc-alpha@...rceware.org, Steven Rostedt <rostedt@...dmis.org>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH 2/4] selftests/rseq: Add sched_state rseq field and getter

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@...icios.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