diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 87f7418..4edae52 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1129,15 +1129,10 @@ static void assigned_dev_update_msi(PCIDevice *pci_dev, unsigned int ctrl_pos)
 #endif
 
 #ifdef KVM_CAP_DEVICE_MSIX
-static int assigned_dev_update_msix_mmio(PCIDevice *pci_dev)
+static int get_msix_entries_max_nr(AssignedDevice *adev)
 {
-    AssignedDevice *adev = container_of(pci_dev, AssignedDevice, dev);
-    uint16_t entries_nr = 0, entries_max_nr;
-    int pos = 0, i, r = 0;
-    uint32_t msg_addr, msg_upper_addr, msg_data, msg_ctrl;
-    struct kvm_assigned_msix_nr msix_nr;
-    struct kvm_assigned_msix_entry msix_entry;
-    void *va = adev->msix_table_page;
+    int pos, entries_max_nr;
+    PCIDevice *pci_dev = &adev->dev;
 
     if (adev->cap.available & ASSIGNED_DEVICE_CAP_MSI)
         pos = pci_dev->cap.start + PCI_CAPABILITY_CONFIG_MSI_LENGTH;
@@ -1148,6 +1143,17 @@ static int assigned_dev_update_msix_mmio(PCIDevice *pci_dev)
     entries_max_nr &= PCI_MSIX_TABSIZE;
     entries_max_nr += 1;
 
+    return entries_max_nr;
+}
+
+static int get_msix_valid_entries_nr(AssignedDevice *adev,
+				     uint16_t entries_max_nr)
+{
+    void *va = adev->msix_table_page;
+    uint32_t msg_data, msg_ctrl;
+    uint16_t entries_nr = 0;
+    int i;
+
     /* Get the usable entry number for allocating */
     for (i = 0; i < entries_max_nr; i++) {
         memcpy(&msg_ctrl, va + i * 16 + 12, 4);
@@ -1157,11 +1163,20 @@ static int assigned_dev_update_msix_mmio(PCIDevice *pci_dev)
             continue;
         entries_nr ++;
     }
+    return entries_nr;
+}
+
+static int assigned_dev_update_msix_mmio(PCIDevice *pci_dev,
+                                         uint16_t entries_nr,
+                                         uint16_t entries_max_nr)
+{
+    AssignedDevice *adev = container_of(pci_dev, AssignedDevice, dev);
+    int i, r = 0;
+    uint32_t msg_addr, msg_upper_addr, msg_data, msg_ctrl;
+    struct kvm_assigned_msix_nr msix_nr;
+    struct kvm_assigned_msix_entry msix_entry;
+    void *va = adev->msix_table_page;
 
-    if (entries_nr == 0) {
-        fprintf(stderr, "MSI-X entry number is zero!\n");
-        return -EINVAL;
-    }
     msix_nr.assigned_dev_id = calc_assigned_dev_id(adev->h_segnr, adev->h_busnr,
                                           (uint8_t)adev->h_devfn);
     msix_nr.entry_nr = entries_nr;
@@ -1203,8 +1218,8 @@ static int assigned_dev_update_msix_mmio(PCIDevice *pci_dev)
         adev->entry[entries_nr].u.msi.address_lo = msg_addr;
         adev->entry[entries_nr].u.msi.address_hi = msg_upper_addr;
         adev->entry[entries_nr].u.msi.data = msg_data;
-        DEBUG("MSI-X data 0x%x, MSI-X addr_lo 0x%x\n!", msg_data, msg_addr);
-	kvm_add_routing_entry(kvm_context, &adev->entry[entries_nr]);
+        DEBUG("MSI-X data 0x%x, MSI-X addr_lo 0x%x\n", msg_data, msg_addr);
+        kvm_add_routing_entry(kvm_context, &adev->entry[entries_nr]);
 
         msix_entry.gsi = adev->entry[entries_nr].gsi;
         msix_entry.entry = i;
@@ -1226,12 +1241,12 @@ static int assigned_dev_update_msix_mmio(PCIDevice *pci_dev)
     return r;
 }
 
-static void assigned_dev_update_msix(PCIDevice *pci_dev, unsigned int ctrl_pos)
+static void assigned_dev_update_msix(PCIDevice *pci_dev, int enable_msix)
 {
     struct kvm_assigned_irq assigned_irq_data;
     AssignedDevice *assigned_dev = container_of(pci_dev, AssignedDevice, dev);
-    uint16_t *ctrl_word = (uint16_t *)(pci_dev->config + ctrl_pos);
     int r;
+    uint16_t entries_nr, entries_max_nr;
 
     memset(&assigned_irq_data, 0, sizeof assigned_irq_data);
     assigned_irq_data.assigned_dev_id  =
@@ -1242,8 +1257,7 @@ static void assigned_dev_update_msix(PCIDevice *pci_dev, unsigned int ctrl_pos)
      * try to catch this by only deassigning irqs if the guest is using
      * MSIX or intends to start. */
     if ((assigned_dev->irq_requested_type & KVM_DEV_IRQ_GUEST_MSIX) ||
-        (*ctrl_word & PCI_MSIX_ENABLE)) {
-
+            enable_msix) {
         assigned_irq_data.flags = assigned_dev->irq_requested_type;
         free_dev_irq_entries(assigned_dev);
         r = kvm_deassign_irq(kvm_context, &assigned_irq_data);
@@ -1254,14 +1268,25 @@ static void assigned_dev_update_msix(PCIDevice *pci_dev, unsigned int ctrl_pos)
         assigned_dev->irq_requested_type = 0;
     }
 
-    if (*ctrl_word & PCI_MSIX_ENABLE) {
-        assigned_irq_data.flags = KVM_DEV_IRQ_HOST_MSIX |
-                                  KVM_DEV_IRQ_GUEST_MSIX;
-
-        if (assigned_dev_update_msix_mmio(pci_dev) < 0) {
+    entries_max_nr = get_msix_entries_max_nr(assigned_dev);
+    if (entries_max_nr == 0) {
+        fprintf(stderr, "assigned_dev_update_msix: MSI-X entries_max_nr == 0");
+        return;
+    }
+    entries_nr = get_msix_valid_entries_nr(assigned_dev, entries_max_nr);
+    if (entries_nr == 0) {
+        if (enable_msix)
+            fprintf(stderr, "MSI-X entry number is zero!\n");
+        return;
+    }
+    if (enable_msix) {
+        if (assigned_dev_update_msix_mmio(pci_dev,
+                    entries_nr, entries_max_nr) < 0) {
             perror("assigned_dev_update_msix_mmio");
             return;
         }
+        assigned_irq_data.flags = KVM_DEV_IRQ_HOST_MSIX |
+                                  KVM_DEV_IRQ_GUEST_MSIX;
         if (kvm_assign_irq(kvm_context, &assigned_irq_data) < 0) {
             perror("assigned_dev_enable_msix: assign irq");
             return;
@@ -1277,6 +1302,7 @@ static void assigned_device_pci_cap_write_config(PCIDevice *pci_dev, uint32_t ad
 {
     AssignedDevice *assigned_dev = container_of(pci_dev, AssignedDevice, dev);
     unsigned int pos = pci_dev->cap.start, ctrl_pos;
+    uint16_t *ctrl_word;
 
     pci_default_cap_write_config(pci_dev, address, val, len);
 #ifdef KVM_CAP_IRQ_ROUTING
@@ -1293,7 +1319,8 @@ static void assigned_device_pci_cap_write_config(PCIDevice *pci_dev, uint32_t ad
         ctrl_pos = pos + 3;
         if (address <= ctrl_pos && address + len > ctrl_pos) {
             ctrl_pos--; /* control is word long */
-            assigned_dev_update_msix(pci_dev, ctrl_pos);
+            ctrl_word = (uint16_t *)(pci_dev->config + ctrl_pos);
+            assigned_dev_update_msix(pci_dev, (*ctrl_word & PCI_MSIX_ENABLE));
 	}
         pos += PCI_CAPABILITY_CONFIG_MSIX_LENGTH;
     }
