KVM: arm64: pvtime: Ensure task delay accounting is enabled

Ensure we're actually accounting run_delay before we claim that we'll
expose it to the guest. If we're not, then we just pretend like steal
time isn't supported in order to avoid any confusion.
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200622142710.18677-1-drjones@redhat.com

arch/arm64/kvm/pvtime.c

@@ -3,6 +3,7 @@
 
 #include <linux/arm-smccc.h>
 #include <linux/kvm_host.h>
+#include <linux/sched/stat.h>
 
 #include <asm/kvm_mmu.h>
 #include <asm/pvclock-abi.h>
@@ -73,6 +74,11 @@ gpa_t kvm_init_stolen_time(struct kvm_vcpu *vcpu)
 	return base;
 }
 
+static bool kvm_arm_pvtime_supported(void)
+{
+	return !!sched_info_on();
+}
+
 int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu,
 			    struct kvm_device_attr *attr)
 {
@@ -82,7 +88,8 @@ int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu,
 	int ret = 0;
 	int idx;
 
-	if (attr->attr != KVM_ARM_VCPU_PVTIME_IPA)
+	if (!kvm_arm_pvtime_supported() ||
+	    attr->attr != KVM_ARM_VCPU_PVTIME_IPA)
 		return -ENXIO;
 
 	if (get_user(ipa, user))
@@ -110,7 +117,8 @@ int kvm_arm_pvtime_get_attr(struct kvm_vcpu *vcpu,
 	u64 __user *user = (u64 __user *)attr->addr;
 	u64 ipa;
 
-	if (attr->attr != KVM_ARM_VCPU_PVTIME_IPA)
+	if (!kvm_arm_pvtime_supported() ||
+	    attr->attr != KVM_ARM_VCPU_PVTIME_IPA)
 		return -ENXIO;
 
 	ipa = vcpu->arch.steal.base;
@@ -125,7 +133,8 @@ int kvm_arm_pvtime_has_attr(struct kvm_vcpu *vcpu,
 {
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_PVTIME_IPA:
-		return 0;
+		if (kvm_arm_pvtime_supported())
+			return 0;
 	}
 	return -ENXIO;
 }