diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 0796719..8808500 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -552,6 +552,10 @@ static QEMUMachine pc_i440fx_machine_v2_3 = {
     PC_I440FX_2_3_MACHINE_OPTIONS,
     .name = "pc-i440fx-2.3",
     .init = pc_init_pci_2_3,
+    .compat_props = (GlobalProperty[]) {
+        HW_COMPAT_2_3,
+        { /* end of list */ }
+    },
 };
 
 #define PC_I440FX_2_2_MACHINE_OPTIONS PC_I440FX_2_3_MACHINE_OPTIONS
@@ -560,6 +564,10 @@ static QEMUMachine pc_i440fx_machine_v2_2 = {
     PC_I440FX_2_2_MACHINE_OPTIONS,
     .name = "pc-i440fx-2.2",
     .init = pc_init_pci_2_2,
+    .compat_props = (GlobalProperty[]) {
+        HW_COMPAT_2_2,
+        { /* end of list */ }
+    },
 };
 
 #define PC_I440FX_2_1_MACHINE_OPTIONS                           \
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index a8a34a4..4a34349 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -448,6 +448,10 @@ static QEMUMachine pc_q35_machine_v2_3 = {
     PC_Q35_2_3_MACHINE_OPTIONS,
     .name = "pc-q35-2.3",
     .init = pc_q35_init_2_3,
+    .compat_props = (GlobalProperty[]) {
+        HW_COMPAT_2_3,
+        { /* end of list */ }
+    },
 };
 
 #define PC_Q35_2_2_MACHINE_OPTIONS PC_Q35_2_3_MACHINE_OPTIONS
@@ -456,6 +460,10 @@ static QEMUMachine pc_q35_machine_v2_2 = {
     PC_Q35_2_2_MACHINE_OPTIONS,
     .name = "pc-q35-2.2",
     .init = pc_q35_init_2_2,
+    .compat_props = (GlobalProperty[]) {
+        HW_COMPAT_2_2,
+        { /* end of list */ }
+    },
 };
 
 #define PC_Q35_2_1_MACHINE_OPTIONS                      \
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 5f25dd3..853a5cc 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1794,12 +1794,16 @@ static const TypeInfo spapr_machine_info = {
     },
 };
 
+#define SPAPR_COMPAT_2_3 \
+        HW_COMPAT_2_3
+
 #define SPAPR_COMPAT_2_2 \
+        SPAPR_COMPAT_2_3, \
         {\
             .driver   = TYPE_SPAPR_PCI_HOST_BRIDGE,\
             .property = "mem_win_size",\
             .value    = "0x20000000",\
-        }
+        } \
 
 #define SPAPR_COMPAT_2_1 \
         SPAPR_COMPAT_2_2
@@ -1883,10 +1887,15 @@ static const TypeInfo spapr_machine_2_2_info = {
 
 static void spapr_machine_2_3_class_init(ObjectClass *oc, void *data)
 {
+    static GlobalProperty compat_props[] = {
+        SPAPR_COMPAT_2_3,
+        { /* end of list */ }
+    };
     MachineClass *mc = MACHINE_CLASS(oc);
 
     mc->name = "pseries-2.3";
     mc->desc = "pSeries Logical Partition (PAPR compliant) v2.3";
+    mc->compat_props = compat_props;
 }
 
 static const TypeInfo spapr_machine_2_3_info = {
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 4a5febb..f4cd405 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -925,7 +925,7 @@ static void virtio_pci_device_plugged(DeviceState *d)
     VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
     VirtioBusState *bus = &proxy->bus;
     uint8_t *config;
-    uint32_t size;
+    uint32_t size, bar_size;
 
     config = proxy->pci_dev.config;
     if (proxy->class_code) {
@@ -936,8 +936,19 @@ static void virtio_pci_device_plugged(DeviceState *d)
     pci_set_word(config + PCI_SUBSYSTEM_ID, virtio_bus_get_vdev_id(bus));
     config[PCI_INTERRUPT_PIN] = 1;
 
+    if (proxy->flags & VIRTIO_PCI_FLAG_AUTO_MSIX_SIZE) {
+        bar_size = proxy->nvectors * PCI_MSIX_ENTRY_SIZE * 2;
+        if (bar_size & (bar_size - 1)) {
+            bar_size = 1 << qemu_fls(bar_size);
+        }
+    } else {
+        /* For migration compatibility */
+        bar_size = 4096;
+    }
+
     if (proxy->nvectors &&
-        msix_init_exclusive_bar(&proxy->pci_dev, proxy->nvectors, 1, 4096)) {
+        msix_init_exclusive_bar(&proxy->pci_dev, proxy->nvectors, 1,
+                                bar_size)) {
         error_report("unable to init msix vectors to %" PRIu32,
                      proxy->nvectors);
         proxy->nvectors = 0;
@@ -1370,6 +1381,8 @@ static const TypeInfo virtio_serial_pci_info = {
 static Property virtio_net_properties[] = {
     DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                     VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
+    DEFINE_PROP_BIT("auto_msix_bar_size", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_AUTO_MSIX_SIZE_BIT, true),
     DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
     DEFINE_VIRTIO_NET_FEATURES(VirtIOPCIProxy, host_features),
     DEFINE_PROP_END_OF_LIST(),
diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index 3bac016..82a6782 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -62,6 +62,9 @@ typedef struct VirtioBusClass VirtioPCIBusClass;
  * vcpu thread using ioeventfd for some devices. */
 #define VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT 1
 #define VIRTIO_PCI_FLAG_USE_IOEVENTFD   (1 << VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT)
+#define VIRTIO_PCI_FLAG_AUTO_MSIX_SIZE_BIT 2
+#define VIRTIO_PCI_FLAG_AUTO_MSIX_SIZE \
+    (1 << VIRTIO_PCI_FLAG_AUTO_MSIX_SIZE_BIT)
 
 typedef struct {
     MSIMessage msg;
diff --git a/include/hw/compat.h b/include/hw/compat.h
index 313682a..3186275 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -1,7 +1,18 @@
 #ifndef HW_COMPAT_H
 #define HW_COMPAT_H
 
+#define HW_COMPAT_2_3 \
+        {\
+            .driver   = "virtio-net-pci",\
+            .property = "auto_msix_bar_size",\
+            .value    = "off",\
+        }
+
+#define HW_COMPAT_2_2 \
+        HW_COMPAT_2_3
+
 #define HW_COMPAT_2_1 \
+        HW_COMPAT_2_2, \
         {\
             .driver   = "intel-hda",\
             .property = "old_msi_addr",\
