LoongArch: KVM: Implement function kvm_para_has_feature()

Implement function kvm_para_has_feature() to detect supported paravirt
features. It can be used by device driver to detect and enable paravirt
features, such as the EIOINTC irqchip driver is able to detect feature
KVM_FEATURE_VIRT_EXTIOI and do some optimization.
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/kvm_para.h

@@ -156,10 +156,20 @@ static __always_inline long kvm_hypercall5(u64 fid,
 	return ret;
 }
 
+#ifdef CONFIG_PARAVIRT
+bool kvm_para_available(void);
+unsigned int kvm_arch_para_features(void);
+#else
+static inline bool kvm_para_available(void)
+{
+	return false;
+}
+
 static inline unsigned int kvm_arch_para_features(void)
 {
 	return 0;
 }
+#endif
 
 static inline unsigned int kvm_arch_para_hints(void)
 {

arch/loongarch/kernel/paravirt.c

@@ -152,11 +152,14 @@ static void pv_init_ipi(void)
 }
 #endif
 
-static bool kvm_para_available(void)
+bool kvm_para_available(void)
 {
 	int config;
 	static int hypervisor_type;
 
+	if (!cpu_has_hypervisor)
+		return false;
+
 	if (!hypervisor_type) {
 		config = read_cpucfg(CPUCFG_KVM_SIG);
 		if (!memcmp(&config, KVM_SIGNATURE, 4))
@@ -166,17 +169,22 @@ static bool kvm_para_available(void)
 	return hypervisor_type == HYPERVISOR_KVM;
 }
 
-int __init pv_ipi_init(void)
+unsigned int kvm_arch_para_features(void)
 {
-	int feature;
+	static unsigned int feature;
 
-	if (!cpu_has_hypervisor)
-		return 0;
 	if (!kvm_para_available())
 		return 0;
 
-	feature = read_cpucfg(CPUCFG_KVM_FEATURE);
-	if (!(feature & BIT(KVM_FEATURE_IPI)))
+	if (!feature)
+		feature = read_cpucfg(CPUCFG_KVM_FEATURE);
+
+	return feature;
+}
+
+int __init pv_ipi_init(void)
+{
+	if (!kvm_para_has_feature(KVM_FEATURE_IPI))
 		return 0;
 
 #ifdef CONFIG_SMP
@@ -259,15 +267,9 @@ static struct notifier_block pv_reboot_nb = {
 
 int __init pv_time_init(void)
 {
-	int r, feature;
-
-	if (!cpu_has_hypervisor)
-		return 0;
-	if (!kvm_para_available())
-		return 0;
+	int r;
 
-	feature = read_cpucfg(CPUCFG_KVM_FEATURE);
-	if (!(feature & BIT(KVM_FEATURE_STEAL_TIME)))
+	if (!kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
 		return 0;
 
 	has_steal_clock = 1;