KVM: arm/arm64: Ensure vcpu target is unset on reset failure

A failed KVM_ARM_VCPU_INIT should not set the vcpu target,
as the vcpu target is used by kvm_vcpu_initialized() to
determine if other vcpu ioctls may proceed. We need to set
the target before calling kvm_reset_vcpu(), but if that call
fails, we should then unset it and clear the feature bitmap
while we're at it.
Signed-off-by: Andrew Jones <drjones@redhat.com>
[maz: Simplified patch, completed commit message]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

virt/kvm/arm/arm.c

@@ -934,7 +934,7 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level,
 static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
 			       const struct kvm_vcpu_init *init)
 {
-	unsigned int i;
+	unsigned int i, ret;
 	int phys_target = kvm_target_cpu();
 
 	if (init->target != phys_target)
@@ -969,9 +969,14 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
 	vcpu->arch.target = phys_target;
 
 	/* Now we know what it is, we can reset it. */
-	return kvm_reset_vcpu(vcpu);
-}
+	ret = kvm_reset_vcpu(vcpu);
+	if (ret) {
+		vcpu->arch.target = -1;
+		bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
+	}
 
+	return ret;
+}
 
 static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
 					 struct kvm_vcpu_init *init)