linux-kernel - [RFC PATCH v4 02/17] cpumask: Introduce cpu_paravirt

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Message-ID: <20251119062100.1112520-3-sshegde@linux.ibm.com>
Date: Wed, 19 Nov 2025 11:50:45 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc: sshegde@...ux.ibm.com, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org, tglx@...utronix.de,
        yury.norov@...il.com, maddy@...ux.ibm.com, srikar@...ux.ibm.com,
        gregkh@...uxfoundation.org, pbonzini@...hat.com, seanjc@...gle.com,
        kprateek.nayak@....com, vschneid@...hat.com, iii@...ux.ibm.com,
        huschle@...ux.ibm.com, rostedt@...dmis.org, dietmar.eggemann@....com,
        christophe.leroy@...roup.eu
Subject: [RFC PATCH v4 02/17] cpumask: Introduce cpu_paravirt_mask

This patch does
- Declare and Define cpu_paravirt_mask.
- Get/Set helpers for it.

Values are set by arch code and consumed by the scheduler.

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 include/linux/cpumask.h | 20 ++++++++++++++++++++
 kernel/sched/core.c     |  5 +++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index ff8f41ab7ce6..079903851341 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -1270,6 +1270,26 @@ static __always_inline bool cpu_dying(unsigned int cpu)
 
 #endif /* NR_CPUS > 1 */
 
+/*
+ * All related wrappers kept together to avoid too many ifdefs
+ * See Documentation/scheduler/sched-arch.rst for details
+ */
+#ifdef CONFIG_PARAVIRT
+extern struct cpumask __cpu_paravirt_mask;
+#define cpu_paravirt_mask    ((const struct cpumask *)&__cpu_paravirt_mask)
+#define set_cpu_paravirt(cpu, paravirt) assign_cpu((cpu), &__cpu_paravirt_mask, (paravirt))
+
+static __always_inline bool cpu_paravirt(unsigned int cpu)
+{
+	return cpumask_test_cpu(cpu, cpu_paravirt_mask);
+}
+#else
+static __always_inline bool cpu_paravirt(unsigned int cpu)
+{
+	return false;
+}
+#endif
+
 #define cpu_is_offline(cpu)	unlikely(!cpu_online(cpu))
 
 #if NR_CPUS <= BITS_PER_LONG
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9f10cfbdc228..40db5e659994 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10852,3 +10852,8 @@ void sched_change_end(struct sched_change_ctx *ctx)
 		p->sched_class->prio_changed(rq, p, ctx->prio);
 	}
 }
+
+#ifdef CONFIG_PARAVIRT
+struct cpumask __cpu_paravirt_mask __read_mostly;
+EXPORT_SYMBOL(__cpu_paravirt_mask);
+#endif
-- 
2.47.3