[PATCH v3 2/2] LoongArch: Add paravirt support with vcpu_is_preempted() in guest side

[Bibo Mao]

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 <maob...@loongson.cn>
---
 arch/loongarch/include/asm/qspinlock.h |  3 +++
 arch/loongarch/kernel/paravirt.c       | 23 ++++++++++++++++++++++-
 2 files changed, 25 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..b61a93c6aec8 100644
--- a/arch/loongarch/kernel/paravirt.c
+++ b/arch/loongarch/kernel/paravirt.c
@@ -246,6 +246,7 @@ static void pv_disable_steal_time(void)
 }
 
 #ifdef CONFIG_SMP
+static DEFINE_STATIC_KEY_FALSE(virt_preempt_key);
 static int pv_time_cpu_online(unsigned int cpu)
 {
        unsigned long flags;
@@ -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 +334,12 @@ int __init pv_time_init(void)
                static_key_slow_inc(&paravirt_steal_rq_enabled);
 #endif
 
-       pr_info("Using paravirt steal-time\n");
+#ifdef CONFIG_SMP
+       if (static_key_enabled(&virt_preempt_key))
+               pr_info("Using paravirt steal-time with preempt enabled\n");
+       else
+#endif
+               pr_info("Using paravirt steal-time with preempt disabled\n");
 
        return 0;
 }
-- 
2.39.3