linux-kernel - [PATCH v4 2/2] LoongArch: Add paravirt support with vcpu_is

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Message-Id: <20251219063021.1778659-3-maobibo@loongson.cn>
Date: Fri, 19 Dec 2025 14:30:21 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Juergen Gross <jgross@...e.com>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>,
	WANG Xuerui <kernel@...0n.name>
Cc: kvm@...r.kernel.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/2] LoongArch: Add paravirt support with vcpu_is_preempted() in guest side

Function vcpu_is_preempted() is used to check whether vCPU is preempted
or not. Here add implementation with vcpu_is_preempted() when option
CONFIG_PARAVIRT is enabled.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
Acked-by: Juergen Gross <jgross@...e.com>
---
 arch/loongarch/include/asm/qspinlock.h |  3 +++
 arch/loongarch/kernel/paravirt.c       | 21 ++++++++++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/qspinlock.h b/arch/loongarch/include/asm/qspinlock.h
index e76d3aa1e1eb..fa3eaf7e48f2 100644
--- a/arch/loongarch/include/asm/qspinlock.h
+++ b/arch/loongarch/include/asm/qspinlock.h
@@ -34,6 +34,9 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
 	return true;
 }
 
+#define vcpu_is_preempted	vcpu_is_preempted
+bool vcpu_is_preempted(int cpu);
+
 #endif /* CONFIG_PARAVIRT */
 
 #include <asm-generic/qspinlock.h>
diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
index b1b51f920b23..a81a3e871dd1 100644
--- a/arch/loongarch/kernel/paravirt.c
+++ b/arch/loongarch/kernel/paravirt.c
@@ -12,6 +12,7 @@ static int has_steal_clock;
 struct static_key paravirt_steal_enabled;
 struct static_key paravirt_steal_rq_enabled;
 static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
+static DEFINE_STATIC_KEY_FALSE(virt_preempt_key);
 DEFINE_STATIC_KEY_FALSE(virt_spin_lock_key);
 
 static u64 native_steal_clock(int cpu)
@@ -267,6 +268,18 @@ static int pv_time_cpu_down_prepare(unsigned int cpu)
 
 	return 0;
 }
+
+bool notrace vcpu_is_preempted(int cpu)
+{
+	struct kvm_steal_time *src;
+
+	if (!static_branch_unlikely(&virt_preempt_key))
+		return false;
+
+	src = &per_cpu(steal_time, cpu);
+	return !!(src->preempted & KVM_VCPU_PREEMPTED);
+}
+EXPORT_SYMBOL(vcpu_is_preempted);
 #endif
 
 static void pv_cpu_reboot(void *unused)
@@ -308,6 +321,9 @@ int __init pv_time_init(void)
 		pr_err("Failed to install cpu hotplug callbacks\n");
 		return r;
 	}
+
+	if (kvm_para_has_feature(KVM_FEATURE_PREEMPT))
+		static_branch_enable(&virt_preempt_key);
 #endif
 
 	static_call_update(pv_steal_clock, paravt_steal_clock);
@@ -318,7 +334,10 @@ int __init pv_time_init(void)
 		static_key_slow_inc(&paravirt_steal_rq_enabled);
 #endif
 
-	pr_info("Using paravirt steal-time\n");
+	if (static_key_enabled(&virt_preempt_key))
+		pr_info("Using paravirt steal-time with preempt enabled\n");
+	else
+		pr_info("Using paravirt steal-time with preempt disabled\n");
 
 	return 0;
 }
-- 
2.39.3