LoongArch: KVM: Add hypercall instruction emulation

On LoongArch system, there is a hypercall instruction special for
virtualization. When system executes this instruction on host side,
there is an illegal instruction exception reported, however it will
trap into host when it is executed in VM mode.

When hypercall is emulated, A0 register is set with value
KVM_HCALL_INVALID_CODE, rather than inject EXCCODE_INE invalid
instruction exception. So VM can continue to executing the next code.
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/Kbuild

@@ -26,4 +26,3 @@ generic-y += poll.h
 generic-y += param.h
 generic-y += posix_types.h
 generic-y += resource.h
-generic-y += kvm_para.h

arch/loongarch/include/asm/kvm_para.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_LOONGARCH_KVM_PARA_H
+#define _ASM_LOONGARCH_KVM_PARA_H
+
+/*
+ * LoongArch hypercall return code
+ */
+#define KVM_HCALL_SUCCESS		0
+#define KVM_HCALL_INVALID_CODE		-1UL
+#define KVM_HCALL_INVALID_PARAMETER	-2UL
+
+static inline unsigned int kvm_arch_para_features(void)
+{
+	return 0;
+}
+
+static inline unsigned int kvm_arch_para_hints(void)
+{
+	return 0;
+}
+
+static inline bool kvm_check_and_clear_guest_paused(void)
+{
+	return false;
+}
+
+#endif /* _ASM_LOONGARCH_KVM_PARA_H */

arch/loongarch/kvm/exit.c

@@ -685,6 +685,16 @@ static int kvm_handle_lasx_disabled(struct kvm_vcpu *vcpu)
 	return RESUME_GUEST;
 }
 
+static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
+{
+	update_pc(&vcpu->arch);
+
+	/* Treat it as noop intruction, only set return value */
+	vcpu->arch.gprs[LOONGARCH_GPR_A0] = KVM_HCALL_INVALID_CODE;
+
+	return RESUME_GUEST;
+}
+
 /*
  * LoongArch KVM callback handling for unimplemented guest exiting
  */
@@ -716,6 +726,7 @@ static exit_handle_fn kvm_fault_tables[EXCCODE_INT_START] = {
 	[EXCCODE_LSXDIS]		= kvm_handle_lsx_disabled,
 	[EXCCODE_LASXDIS]		= kvm_handle_lasx_disabled,
 	[EXCCODE_GSPR]			= kvm_handle_gspr,
+	[EXCCODE_HVC]			= kvm_handle_hypercall,
 };
 
 int kvm_handle_fault(struct kvm_vcpu *vcpu, int fault)