linux-kernel - [PATCH 25/30] rseq: Extend struct rseq with per-memory-map NUMA-aware Concurrency ID

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Date:   Tue, 22 Nov 2022 15:39:27 -0500
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>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH 25/30] rseq: Extend struct rseq with per-memory-map NUMA-aware Concurrency ID

Expose a per-memory-map NUMA-aware concurrency ID to userspace. Each
concurrency ID stays associated with the same NUMA node except in case
of NUMA topology reconfiguration.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
---
 include/uapi/linux/rseq.h |  9 +++++++++
 kernel/rseq.c             | 10 +++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index c233aae5eac9..5779249ed37f 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -148,6 +148,15 @@ struct rseq {
 	 */
 	__u32 mm_cid;
 
+	/*
+	 * Restartable sequences mm_numa_cid field. Updated by the kernel.
+	 * Read by user-space with single-copy atomicity semantics. This field
+	 * should only be read by the thread which registered this data
+	 * structure.  Aligned on 32-bit. Contains the current thread's
+	 * NUMA-aware concurrency ID (allocated uniquely within a memory map).
+	 */
+	__u32 mm_numa_cid;
+
 	/*
 	 * Flexible array member at end of structure, after last feature field.
 	 */
diff --git a/kernel/rseq.c b/kernel/rseq.c
index cb2512ab3256..58b09de0de47 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -91,14 +91,17 @@ static int rseq_update_cpu_node_id(struct task_struct *t)
 	u32 cpu_id = raw_smp_processor_id();
 	u32 node_id = cpu_to_node(cpu_id);
 	u32 mm_cid = task_mm_cid(t);
+	u32 mm_numa_cid = task_mm_numa_cid(t);
 
 	WARN_ON_ONCE((int) mm_cid < 0);
+	WARN_ON_ONCE((int) mm_numa_cid < 0);
 	if (!user_write_access_begin(rseq, t->rseq_len))
 		goto efault;
 	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
 	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
 	unsafe_put_user(node_id, &rseq->node_id, efault_end);
 	unsafe_put_user(mm_cid, &rseq->mm_cid, efault_end);
+	unsafe_put_user(mm_numa_cid, &rseq->mm_numa_cid, efault_end);
 	/*
 	 * Additional feature fields added after ORIG_RSEQ_SIZE
 	 * need to be conditionally updated only if
@@ -117,7 +120,7 @@ static int rseq_update_cpu_node_id(struct task_struct *t)
 static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
 {
 	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0,
-	    mm_cid = 0;
+	    mm_cid = 0, mm_numa_cid = 0;
 
 	/*
 	 * Reset cpu_id_start to its initial state (0).
@@ -141,6 +144,11 @@ static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
 	 */
 	if (put_user(mm_cid, &t->rseq->mm_cid))
 		return -EFAULT;
+	/*
+	 * Reset mm_numa_cid to its initial state (0).
+	 */
+	if (put_user(mm_numa_cid, &t->rseq->mm_numa_cid))
+		return -EFAULT;
 	/*
 	 * Additional feature fields added after ORIG_RSEQ_SIZE
 	 * need to be conditionally reset only if
-- 
2.25.1