diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index d479fd22f573..2d703c8a712a 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -831,6 +831,7 @@ static int nvme_init(PCIDevice *pci_dev)
 {
     NvmeCtrl *n = NVME(pci_dev);
     NvmeIdCtrl *id = &n->id_ctrl;
+    Error *err = NULL;
 
     int i;
     int64_t bs_size;
@@ -872,7 +873,9 @@ static int nvme_init(PCIDevice *pci_dev)
     pci_register_bar(&n->parent_obj, 0,
         PCI_BASE_ADDRESS_SPACE_MEMORY | PCI_BASE_ADDRESS_MEM_TYPE_64,
         &n->iomem);
-    msix_init_exclusive_bar(&n->parent_obj, n->num_queues, 4);
+    if (msix_init_exclusive_bar(&n->parent_obj, n->num_queues, 4, &err)) {
+        error_report_err(err);
+    }
 
     id->vid = cpu_to_le16(pci_get_word(pci_conf + PCI_VENDOR_ID));
     id->ssvid = cpu_to_le16(pci_get_word(pci_conf + PCI_SUBSYSTEM_VENDOR_ID));
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index abeaf3da0800..70e71a597b9c 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -749,13 +749,13 @@ static void ivshmem_reset(DeviceState *d)
     }
 }
 
-static int ivshmem_setup_interrupts(IVShmemState *s)
+static int ivshmem_setup_interrupts(IVShmemState *s, Error **errp)
 {
     /* allocate QEMU callback data for receiving interrupts */
     s->msi_vectors = g_malloc0(s->vectors * sizeof(MSIVector));
 
     if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
-        if (msix_init_exclusive_bar(PCI_DEVICE(s), s->vectors, 1)) {
+        if (msix_init_exclusive_bar(PCI_DEVICE(s), s->vectors, 1, errp)) {
             return -1;
         }
 
@@ -897,8 +897,8 @@ static void ivshmem_common_realize(PCIDevice *dev, Error **errp)
         qemu_chr_fe_set_handlers(&s->server_chr, ivshmem_can_receive,
                                  ivshmem_read, NULL, s, NULL, true);
 
-        if (ivshmem_setup_interrupts(s) < 0) {
-            error_setg(errp, "failed to initialize interrupts");
+        if (ivshmem_setup_interrupts(s, errp) < 0) {
+            error_prepend(errp, "Failed to initialize interrupts: ");
             return;
         }
     }
diff --git a/hw/net/e1000e.c b/hw/net/e1000e.c
index 4994e1ca0062..74cbbef30366 100644
--- a/hw/net/e1000e.c
+++ b/hw/net/e1000e.c
@@ -292,7 +292,11 @@ e1000e_init_msix(E1000EState *s)
                         E1000E_MSIX_IDX, E1000E_MSIX_TABLE,
                         &s->msix,
                         E1000E_MSIX_IDX, E1000E_MSIX_PBA,
-                        0xA0);
+                        0xA0, NULL);
+
+    /* Any error other than -ENOTSUP(board's MSI support is broken)
+     * is a programming error. Fall back to INTx silently on -ENOTSUP */
+    assert(!res || res == -ENOTSUP);
 
     if (res < 0) {
         trace_e1000e_msix_init_fail(res);
diff --git a/hw/net/rocker/rocker.c b/hw/net/rocker/rocker.c
index e9d215aa4df1..8f829f2946d8 100644
--- a/hw/net/rocker/rocker.c
+++ b/hw/net/rocker/rocker.c
@@ -1256,14 +1256,19 @@ static int rocker_msix_init(Rocker *r)
 {
     PCIDevice *dev = PCI_DEVICE(r);
     int err;
+    Error *local_err = NULL;
 
     err = msix_init(dev, ROCKER_MSIX_VEC_COUNT(r->fp_ports),
                     &r->msix_bar,
                     ROCKER_PCI_MSIX_BAR_IDX, ROCKER_PCI_MSIX_TABLE_OFFSET,
                     &r->msix_bar,
                     ROCKER_PCI_MSIX_BAR_IDX, ROCKER_PCI_MSIX_PBA_OFFSET,
-                    0);
+                    0, &local_err);
+    /* Any error other than -ENOTSUP(board's MSI support is broken)
+     * is a programming error. */
+    assert(!err || err == -ENOTSUP);
     if (err) {
+        error_report_err(local_err);
         return err;
     }
 
diff --git a/hw/net/vmxnet3.c b/hw/net/vmxnet3.c
index 92f6af9620f1..a433cc017cb1 100644
--- a/hw/net/vmxnet3.c
+++ b/hw/net/vmxnet3.c
@@ -2191,10 +2191,14 @@ vmxnet3_init_msix(VMXNET3State *s)
                         VMXNET3_MSIX_BAR_IDX, VMXNET3_OFF_MSIX_TABLE,
                         &s->msix_bar,
                         VMXNET3_MSIX_BAR_IDX, VMXNET3_OFF_MSIX_PBA(s),
-                        VMXNET3_MSIX_OFFSET(s));
+                        VMXNET3_MSIX_OFFSET(s), NULL);
+
+    /* Any error other than -ENOTSUP(board's MSI support is broken)
+     * is a programming error. Fall back to INTx on -ENOTSUP */
+    assert(!res || res == -ENOTSUP);
 
     if (0 > res) {
-        VMW_WRPRN("Failed to initialize MSI-X, error %d", res);
+        VMW_WRPRN("Failed to initialize MSI-X, board's MSI support is broken");
         s->msix_used = false;
     } else {
         if (!vmxnet3_use_msix_vectors(s, VMXNET3_MAX_INTRS)) {
diff --git a/hw/pci/msix.c b/hw/pci/msix.c
index 0cee631ecc55..d03016f124a9 100644
--- a/hw/pci/msix.c
+++ b/hw/pci/msix.c
@@ -21,6 +21,7 @@
 #include "hw/pci/pci.h"
 #include "hw/xen/xen.h"
 #include "qemu/range.h"
+#include "qapi/error.h"
 
 #define MSIX_CAP_LENGTH 12
 
@@ -238,11 +239,29 @@ static void msix_mask_all(struct PCIDevice *dev, unsigned nentries)
     }
 }
 
-/* Initialize the MSI-X structures */
+/* Make PCI device @dev MSI-X capable
+ * @nentries is the max number of MSI-X vectors that the device support.
+ * @table_bar is the MemoryRegion that MSI-X table structure resides.
+ * @table_bar_nr is number of base address register corresponding to @table_bar.
+ * @table_offset indicates the offset that the MSI-X table structure starts with
+ * in @table_bar.
+ * @pba_bar is the MemoryRegion that the Pending Bit Array structure resides.
+ * @pba_bar_nr is number of base address register corresponding to @pba_bar.
+ * @pba_offset indicates the offset that the Pending Bit Array structure
+ * starts with in @pba_bar.
+ * Non-zero @cap_pos puts capability MSI-X at that offset in PCI config space.
+ * @errp is for returning errors.
+ *
+ * Return 0 on success; set @errp and return -errno on error:
+ * -ENOTSUP means lacking msi support for a msi-capable platform.
+ * -EINVAL means capability overlap, happens when @cap_pos is non-zero,
+ * also means a programming error, except device assignment, which can check
+ * if a real HW is broken.*/
 int msix_init(struct PCIDevice *dev, unsigned short nentries,
               MemoryRegion *table_bar, uint8_t table_bar_nr,
               unsigned table_offset, MemoryRegion *pba_bar,
-              uint8_t pba_bar_nr, unsigned pba_offset, uint8_t cap_pos)
+              uint8_t pba_bar_nr, unsigned pba_offset, uint8_t cap_pos,
+              Error **errp)
 {
     int cap;
     unsigned table_size, pba_size;
@@ -250,10 +269,12 @@ int msix_init(struct PCIDevice *dev, unsigned short nentries,
 
     /* Nothing to do if MSI is not supported by interrupt controller */
     if (!msi_nonbroken) {
+        error_setg(errp, "MSI-X is not supported by interrupt controller");
         return -ENOTSUP;
     }
 
     if (nentries < 1 || nentries > PCI_MSIX_FLAGS_QSIZE + 1) {
+        error_setg(errp, "The number of MSI-X vectors is invalid");
         return -EINVAL;
     }
 
@@ -266,10 +287,13 @@ int msix_init(struct PCIDevice *dev, unsigned short nentries,
         table_offset + table_size > memory_region_size(table_bar) ||
         pba_offset + pba_size > memory_region_size(pba_bar) ||
         (table_offset | pba_offset) & PCI_MSIX_FLAGS_BIRMASK) {
+        error_setg(errp, "table & pba overlap, or they don't fit in BARs,"
+                   " or don't align");
         return -EINVAL;
     }
 
-    cap = pci_add_capability(dev, PCI_CAP_ID_MSIX, cap_pos, MSIX_CAP_LENGTH);
+    cap = pci_add_capability2(dev, PCI_CAP_ID_MSIX,
+                              cap_pos, MSIX_CAP_LENGTH, errp);
     if (cap < 0) {
         return cap;
     }
@@ -306,7 +330,7 @@ int msix_init(struct PCIDevice *dev, unsigned short nentries,
 }
 
 int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
-                            uint8_t bar_nr)
+                            uint8_t bar_nr, Error **errp)
 {
     int ret;
     char *name;
@@ -338,7 +362,7 @@ int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
     ret = msix_init(dev, nentries, &dev->msix_exclusive_bar, bar_nr,
                     0, &dev->msix_exclusive_bar,
                     bar_nr, bar_pba_offset,
-                    0);
+                    0, errp);
     if (ret) {
         return ret;
     }
diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
index 67fc1e7893f8..a946424ab234 100644
--- a/hw/scsi/megasas.c
+++ b/hw/scsi/megasas.c
@@ -2366,9 +2366,12 @@ static void megasas_scsi_realize(PCIDevice *dev, Error **errp)
 
     if (megasas_use_msix(s) &&
         msix_init(dev, 15, &s->mmio_io, b->mmio_bar, 0x2000,
-                  &s->mmio_io, b->mmio_bar, 0x3800, 0x68)) {
+                  &s->mmio_io, b->mmio_bar, 0x3800, 0x68, &err)) {
+        /*TODO: check msix_init's error, and should fail on msix=on */
+        error_report_err(err);
         s->msix = ON_OFF_AUTO_OFF;
     }
+
     if (pci_is_express(dev)) {
         pcie_endpoint_cap_init(dev, 0xa0);
     }
diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index 0ace273da472..153b006ca01b 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -3703,11 +3703,14 @@ static void usb_xhci_realize(struct PCIDevice *dev, Error **errp)
     }
 
     if (xhci->msix != ON_OFF_AUTO_OFF) {
-        /* TODO check for errors */
-        msix_init(dev, xhci->numintrs,
-                  &xhci->mem, 0, OFF_MSIX_TABLE,
-                  &xhci->mem, 0, OFF_MSIX_PBA,
-                  0x90);
+        /* TODO check for errors, and should fail when msix=on */
+        ret = msix_init(dev, xhci->numintrs,
+                        &xhci->mem, 0, OFF_MSIX_TABLE,
+                        &xhci->mem, 0, OFF_MSIX_PBA,
+                        0x90, &err);
+        if (ret) {
+            error_report_err(err);
+        }
     }
 }
 
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index d7dbe0e3e04e..0bcfaad0a095 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1432,6 +1432,7 @@ static void vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
 static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
 {
     int ret;
+    Error *local_err = NULL;
 
     vdev->msix->pending = g_malloc0(BITS_TO_LONGS(vdev->msix->entries) *
                                     sizeof(unsigned long));
@@ -1439,12 +1440,15 @@ static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
                     vdev->bars[vdev->msix->table_bar].region.mem,
                     vdev->msix->table_bar, vdev->msix->table_offset,
                     vdev->bars[vdev->msix->pba_bar].region.mem,
-                    vdev->msix->pba_bar, vdev->msix->pba_offset, pos);
+                    vdev->msix->pba_bar, vdev->msix->pba_offset, pos,
+                    &local_err);
     if (ret < 0) {
         if (ret == -ENOTSUP) {
+            error_report_err(local_err);
             return 0;
         }
-        error_setg(errp, "msix_init failed");
+
+        error_propagate(errp, local_err);
         return ret;
     }
 
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 21c2b9dbfc97..9562c265aa26 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1670,13 +1670,12 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
 
     if (proxy->nvectors) {
         int err = msix_init_exclusive_bar(&proxy->pci_dev, proxy->nvectors,
-                                          proxy->msix_bar_idx);
+                                          proxy->msix_bar_idx, errp);
+        /* Any error other than -ENOTSUP(board's MSI support is broken)
+         * is a programming error. */
+        assert(!err || err == -ENOTSUP);
         if (err) {
-            /* Notice when a system that supports MSIx can't initialize it.  */
-            if (err != -ENOTSUP) {
-                error_report("unable to init msix vectors to %" PRIu32,
-                             proxy->nvectors);
-            }
+            error_report_err(*errp);
             proxy->nvectors = 0;
         }
     }
diff --git a/include/hw/pci/msix.h b/include/hw/pci/msix.h
index 048a29dd2f65..1f27658d352f 100644
--- a/include/hw/pci/msix.h
+++ b/include/hw/pci/msix.h
@@ -9,9 +9,10 @@ MSIMessage msix_get_message(PCIDevice *dev, unsigned int vector);
 int msix_init(PCIDevice *dev, unsigned short nentries,
               MemoryRegion *table_bar, uint8_t table_bar_nr,
               unsigned table_offset, MemoryRegion *pba_bar,
-              uint8_t pba_bar_nr, unsigned pba_offset, uint8_t cap_pos);
+              uint8_t pba_bar_nr, unsigned pba_offset, uint8_t cap_pos,
+              Error **errp);
 int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
-                            uint8_t bar_nr);
+                            uint8_t bar_nr, Error **errp);
 
 void msix_write_config(PCIDevice *dev, uint32_t address, uint32_t val, int len);
 
