diff --git a/hypervisor/arch/x86/assign.c b/hypervisor/arch/x86/assign.c
index 4fe7cbc98..9f284e01a 100644
--- a/hypervisor/arch/x86/assign.c
+++ b/hypervisor/arch/x86/assign.c
@@ -55,12 +55,16 @@ ptirq_lookup_entry_by_vpin(struct acrn_vm *vm, uint8_t virt_pin, bool pic_pin)
 #ifdef CONFIG_COM_IRQ
 static bool ptdev_hv_owned_intx(const struct acrn_vm *vm, const union source_id *virt_sid)
 {
+	bool ret;
+
 	/* vm0 vuart pin is owned by hypervisor under debug version */
 	if (is_vm0(vm) && (virt_sid->intx_id.pin == CONFIG_COM_IRQ)) {
-		return true;
+		ret = true;
 	} else {
-		return false;
+	        ret = false;
 	}
+
+	return ret;
 }
 #endif /* CONFIG_COM_IRQ */
 
@@ -496,37 +500,35 @@ void ptirq_intx_ack(struct acrn_vm *vm, uint8_t virt_pin,
 	bool pic_pin = (vpin_src == PTDEV_VPIN_PIC);
 
 	entry = ptirq_lookup_entry_by_vpin(vm, virt_pin, pic_pin);
-	if (entry == NULL) {
-		return;
-	}
+	if (entry != NULL) {
+		phys_irq = entry->allocated_pirq;
 
-	phys_irq = entry->allocated_pirq;
-
-	/* NOTE: only Level trigger will process EOI/ACK and if we got here
-	 * means we have this vioapic or vpic or both enabled
-	 */
-	switch (vpin_src) {
-	case PTDEV_VPIN_IOAPIC:
-		if (entry->polarity != 0U) {
-			vioapic_set_irq(vm, virt_pin, GSI_SET_HIGH);
-		} else {
-			vioapic_set_irq(vm, virt_pin, GSI_SET_LOW);
-		}
-		break;
-	case PTDEV_VPIN_PIC:
-		vpic_set_irq(vm, virt_pin, GSI_SET_LOW);
-	default:
-		/*
-		 * In this switch statement, vpin_src shall either be
-		 * PTDEV_VPIN_IOAPIC or PTDEV_VPIN_PIC.
-		 * Gracefully return if prior case clauses have not been met.
+		/* NOTE: only Level trigger will process EOI/ACK and if we got here
+		 * means we have this vioapic or vpic or both enabled
 		 */
-		break;
-	}
+		switch (vpin_src) {
+		case PTDEV_VPIN_IOAPIC:
+			if (entry->polarity != 0U) {
+				vioapic_set_irq(vm, virt_pin, GSI_SET_HIGH);
+			} else {
+				vioapic_set_irq(vm, virt_pin, GSI_SET_LOW);
+			}
+			break;
+		case PTDEV_VPIN_PIC:
+			vpic_set_irq(vm, virt_pin, GSI_SET_LOW);
+		default:
+			/*
+			 * In this switch statement, vpin_src shall either be
+			 * PTDEV_VPIN_IOAPIC or PTDEV_VPIN_PIC.
+			 * Gracefully return if prior case clauses have not been met.
+			 */
+			break;
+		}
 
-	dev_dbg(ACRN_DBG_PTIRQ, "dev-assign: irq=0x%x acked vr: 0x%x",
-			phys_irq, irq_to_vector(phys_irq));
-	gsi_unmask_irq(phys_irq);
+		dev_dbg(ACRN_DBG_PTIRQ, "dev-assign: irq=0x%x acked vr: 0x%x",
+				phys_irq, irq_to_vector(phys_irq));
+		gsi_unmask_irq(phys_irq);
+	}
 }
 
 /* Main entry for PCI device assignment with MSI and MSI-X
diff --git a/hypervisor/arch/x86/virq.c b/hypervisor/arch/x86/virq.c
index aafcd2b4e..ee344ad7d 100644
--- a/hypervisor/arch/x86/virq.c
+++ b/hypervisor/arch/x86/virq.c
@@ -266,29 +266,35 @@ static void vcpu_inject_exception(struct acrn_vcpu *vcpu, uint32_t vector)
 	vcpu_retain_rip(vcpu);
 }
 
-static int vcpu_inject_hi_exception(struct acrn_vcpu *vcpu)
+static int32_t vcpu_inject_hi_exception(struct acrn_vcpu *vcpu)
 {
 	uint32_t vector = vcpu->arch.exception_info.exception;
+	int32_t ret;
 
 	if (vector == IDT_MC || vector == IDT_BP || vector == IDT_DB) {
 		vcpu_inject_exception(vcpu, vector);
-		return 1;
+		ret = 1;
+	} else {
+		ret = 0;
 	}
 
-	return 0;
+	return ret;
 }
 
-static int vcpu_inject_lo_exception(struct acrn_vcpu *vcpu)
+static int32_t vcpu_inject_lo_exception(struct acrn_vcpu *vcpu)
 {
 	uint32_t vector = vcpu->arch.exception_info.exception;
+	int32_t ret;
 
 	/* high priority exception already be injected */
 	if (vector <= NR_MAX_VECTOR) {
 		vcpu_inject_exception(vcpu, vector);
-		return 1;
+	        ret = 1;
+	} else {
+		ret = 0;
 	}
 
-	return 0;
+	return ret;
 }
 
 /* Inject external interrupt to guest */
@@ -357,10 +363,11 @@ int interrupt_window_vmexit_handler(struct acrn_vcpu *vcpu)
 	return 0;
 }
 
-int external_interrupt_vmexit_handler(struct acrn_vcpu *vcpu)
+int32_t external_interrupt_vmexit_handler(struct acrn_vcpu *vcpu)
 {
 	uint32_t intr_info;
 	struct intr_excp_ctx ctx;
+	int32_t ret;
 
 	intr_info = exec_vmread32(VMX_EXIT_INT_INFO);
 	if (((intr_info & VMX_INT_INFO_VALID) == 0U) ||
@@ -368,25 +375,26 @@ int external_interrupt_vmexit_handler(struct acrn_vcpu *vcpu)
 		!= VMX_INT_TYPE_EXT_INT)) {
 		pr_err("Invalid VM exit interrupt info:%x", intr_info);
 		vcpu_retain_rip(vcpu);
-		return -EINVAL;
-	}
-
-	ctx.vector = intr_info & 0xFFU;
-	ctx.rip    = vcpu_get_rip(vcpu);
-	ctx.rflags = vcpu_get_rflags(vcpu);
-	ctx.cs     = exec_vmread32(VMX_GUEST_CS_SEL);
+		ret = -EINVAL;
+	} else {
+		ctx.vector = intr_info & 0xFFU;
+		ctx.rip    = vcpu_get_rip(vcpu);
+		ctx.rflags = vcpu_get_rflags(vcpu);
+		ctx.cs     = exec_vmread32(VMX_GUEST_CS_SEL);
 
 #ifdef CONFIG_PARTITION_MODE
-	partition_mode_dispatch_interrupt(&ctx);
+		partition_mode_dispatch_interrupt(&ctx);
 #else
-	dispatch_interrupt(&ctx);
+		dispatch_interrupt(&ctx);
 #endif
 
-	vcpu_retain_rip(vcpu);
+		vcpu_retain_rip(vcpu);
 
-	TRACE_2L(TRACE_VMEXIT_EXTERNAL_INTERRUPT, ctx.vector, 0UL);
+		TRACE_2L(TRACE_VMEXIT_EXTERNAL_INTERRUPT, ctx.vector, 0UL);
+		ret = 0;
+	}
 
-	return 0;
+	return ret;
 }
 
 int acrn_handle_pending_request(struct acrn_vcpu *vcpu)
diff --git a/hypervisor/arch/x86/vtd.c b/hypervisor/arch/x86/vtd.c
index f3e94cde6..db200762d 100644
--- a/hypervisor/arch/x86/vtd.c
+++ b/hypervisor/arch/x86/vtd.c
@@ -144,11 +144,15 @@ static inline uint8_t* get_ctx_table(uint32_t dmar_index, uint8_t bus_no)
 
 bool iommu_snoop_supported(struct acrn_vm *vm)
 {
+	bool ret;
+
 	if (vm->iommu == NULL || vm->iommu->iommu_snoop) {
-		return true;
+		ret =  true;
+	} else {
+		ret = false;
 	}
 
-	return false;
+	return ret;
 }
 
 static struct dmar_drhd_rt dmar_drhd_units[CONFIG_MAX_IOMMU_NUM];
@@ -267,12 +271,10 @@ static void iommu_flush_cache(const struct dmar_drhd_rt *dmar_unit,
 	uint32_t i;
 
 	/* if vtd support page-walk coherency, no need to flush cacheline */
-	if (iommu_ecap_c(dmar_unit->ecap) != 0U) {
-		return;
-	}
-
-	for (i = 0U; i < size; i += CACHE_LINE_SIZE) {
-		clflush((char *)p + i);
+	if (iommu_ecap_c(dmar_unit->ecap) == 0U) {
+		for (i = 0U; i < size; i += CACHE_LINE_SIZE) {
+			clflush((char *)p + i);
+		}
 	}
 }
 
@@ -478,16 +480,14 @@ static void dmar_write_buffer_flush(struct dmar_drhd_rt *dmar_unit)
 {
 	uint32_t status;
 
-	if (iommu_cap_rwbf(dmar_unit->cap) == 0U) {
-		return;
+	if (iommu_cap_rwbf(dmar_unit->cap) != 0U) {
+		spinlock_obtain(&(dmar_unit->lock));
+		iommu_write32(dmar_unit, DMAR_GCMD_REG, dmar_unit->gcmd | DMA_GCMD_WBF);
+
+		/* read lower 32 bits to check */
+		dmar_wait_completion(dmar_unit, DMAR_GSTS_REG, DMA_GSTS_WBFS, true, &status);
+		spinlock_release(&(dmar_unit->lock));
 	}
-
-	spinlock_obtain(&(dmar_unit->lock));
-	iommu_write32(dmar_unit, DMAR_GCMD_REG, dmar_unit->gcmd | DMA_GCMD_WBF);
-
-	/* read lower 32 bits to check */
-	dmar_wait_completion(dmar_unit, DMAR_GSTS_REG, DMA_GSTS_WBFS, true, &status);
-	spinlock_release(&(dmar_unit->lock));
 }
 
 /*
@@ -687,19 +687,17 @@ static void fault_status_analysis(uint32_t status)
 
 static void fault_record_analysis(__unused uint64_t low, uint64_t high)
 {
-	if (dma_frcd_up_f(high)) {
-		return;
-	}
-
-	/* currently skip PASID related parsing */
-	pr_info("%s, Reason: 0x%x, SID: %x.%x.%x @0x%llx",
-		(dma_frcd_up_t(high) != 0U) ? "Read/Atomic" : "Write", dma_frcd_up_fr(high),
-		pci_bus(dma_frcd_up_sid(high)), pci_slot(dma_frcd_up_sid(high)), pci_func(dma_frcd_up_sid(high)), low);
+	if (!dma_frcd_up_f(high)) {
+		/* currently skip PASID related parsing */
+		pr_info("%s, Reason: 0x%x, SID: %x.%x.%x @0x%llx",
+			(dma_frcd_up_t(high) != 0U) ? "Read/Atomic" : "Write", dma_frcd_up_fr(high),
+			pci_bus(dma_frcd_up_sid(high)), pci_slot(dma_frcd_up_sid(high)), pci_func(dma_frcd_up_sid(high)), low);
 #if DBG_IOMMU
-	if (iommu_ecap_dt(dmar_unit->ecap) != 0U) {
-		pr_info("Address Type: 0x%x", dma_frcd_up_at(high));
-	}
+		if (iommu_ecap_dt(dmar_unit->ecap) != 0U) {
+			pr_info("Address Type: 0x%x", dma_frcd_up_at(high));
+		}
 #endif
+	}
 }
 
 static void dmar_fault_handler(uint32_t irq, void *data)
@@ -1011,25 +1009,25 @@ struct iommu_domain *create_iommu_domain(uint16_t vm_id, uint64_t translation_ta
 
 	if (translation_table == 0UL) {
 		pr_err("translation table is NULL");
-		return NULL;
+	        domain =  NULL;
+	} else {
+		/*
+		 * A hypercall is called to create an iommu domain for a valid VM,
+		 * and hv code limit the VM number to CONFIG_MAX_VM_NUM.
+		 * So the array iommu_domains will not be accessed out of range.
+		 */
+		domain = &iommu_domains[vmid_to_domainid(vm_id)];
+
+		domain->is_host = false;
+		domain->vm_id = vm_id;
+		domain->trans_table_ptr = translation_table;
+		domain->addr_width = addr_width;
+		domain->is_tt_ept = true;
+
+		dev_dbg(ACRN_DBG_IOMMU, "create domain [%d]: vm_id = %hu, ept@0x%x",
+			vmid_to_domainid(domain->vm_id), domain->vm_id, domain->trans_table_ptr);
 	}
 
-	/*
-	 * A hypercall is called to create an iommu domain for a valid VM,
-	 * and hv code limit the VM number to CONFIG_MAX_VM_NUM.
-	 * So the array iommu_domains will not be accessed out of range.
-	 */
-	domain = &iommu_domains[vmid_to_domainid(vm_id)];
-
-	domain->is_host = false;
-	domain->vm_id = vm_id;
-	domain->trans_table_ptr = translation_table;
-	domain->addr_width = addr_width;
-	domain->is_tt_ept = true;
-
-	dev_dbg(ACRN_DBG_IOMMU, "create domain [%d]: vm_id = %hu, ept@0x%x",
-		vmid_to_domainid(domain->vm_id), domain->vm_id, domain->trans_table_ptr);
-
 	return domain;
 }
 
@@ -1105,15 +1103,16 @@ void resume_iommu(void)
 
 int init_iommu(void)
 {
-	int ret = 0;
+	int ret;
 
 	ret = register_hrhd_units();
 	if (ret != 0) {
 		return ret;
+	} else {
+		do_action_for_iommus(dmar_prepare);
+		ret = 0;
 	}
 
-	do_action_for_iommus(dmar_prepare);
-
 	return ret;
 }