KVM: Split vcpu creation to avoid vcpu_load() before preemption setup

Split kvm_arch_vcpu_create() into kvm_arch_vcpu_create() and
kvm_arch_vcpu_setup(), enabling preemption notification between the two.
This mean that we can now do vcpu_load() within kvm_arch_vcpu_setup().
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm.h

@@ -466,6 +466,7 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu);
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id);
+int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu);
 
 int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu);

drivers/kvm/kvm_main.c

@@ -769,6 +769,10 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
 
 	preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);
 
+	r = kvm_arch_vcpu_setup(vcpu);
+	if (r)
+		goto vcpu_destroy;
+
 	mutex_lock(&kvm->lock);
 	if (kvm->vcpus[n]) {
 		r = -EEXIST;

drivers/kvm/x86.c

@@ -2478,13 +2478,12 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
 						unsigned int id)
 {
-	int r;
-	struct kvm_vcpu *vcpu = kvm_x86_ops->vcpu_create(kvm, id);
+	return kvm_x86_ops->vcpu_create(kvm, id);
+}
 
-	if (IS_ERR(vcpu)) {
-		r = -ENOMEM;
-		goto fail;
-	}
+int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
+{
+	int r;
 
 	/* We do fxsave: this must be aligned. */
 	BUG_ON((unsigned long)&vcpu->host_fx_image & 0xF);
@@ -2497,11 +2496,10 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
 	if (r < 0)
 		goto free_vcpu;
 
-	return vcpu;
+	return 0;
 free_vcpu:
 	kvm_x86_ops->vcpu_free(vcpu);
-fail:
-	return ERR_PTR(r);
+	return r;
 }
 
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)