LoongArch: KVM: Implement handle fpu exception

Implement handle fpu exception, using kvm_own_fpu() to enable fpu for
guest.
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kvm/exit.c

@@ -631,3 +631,30 @@ static int kvm_handle_write_fault(struct kvm_vcpu *vcpu)
 {
 	return kvm_handle_rdwr_fault(vcpu, true);
 }
+
+/**
+ * kvm_handle_fpu_disabled() - Guest used fpu however it is disabled at host
+ * @vcpu:	Virtual CPU context.
+ *
+ * Handle when the guest attempts to use fpu which hasn't been allowed
+ * by the root context.
+ */
+static int kvm_handle_fpu_disabled(struct kvm_vcpu *vcpu)
+{
+	struct kvm_run *run = vcpu->run;
+
+	/*
+	 * If guest FPU not present, the FPU operation should have been
+	 * treated as a reserved instruction!
+	 * If FPU already in use, we shouldn't get this at all.
+	 */
+	if (WARN_ON(vcpu->arch.aux_inuse & KVM_LARCH_FPU)) {
+		kvm_err("%s internal error\n", __func__);
+		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		return RESUME_HOST;
+	}
+
+	kvm_own_fpu(vcpu);
+
+	return RESUME_GUEST;
+}