diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index 7d31ded..e77c448 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -977,6 +977,7 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
     S390pciState *s = S390_PCI_HOST_BRIDGE(hotplug_dev);
     PCIDevice *pdev = NULL;
     S390PCIBusDevice *pbdev = NULL;
+    int ret;
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_BRIDGE)) {
         PCIBridge *pb = PCI_BRIDGE(dev);
@@ -1027,6 +1028,20 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
             pbdev->iommu->dma_limit = s390_pci_start_dma_count(s, pbdev);
             /* Fill in CLP information passed via the vfio region */
             s390_pci_get_clp_info(pbdev);
+
+            /*
+             * For a relaxed-alignment device, setup the special I/O region
+             * if available.  Otherwise, the device cannot be passed through.
+             */
+            ret = 0;
+            if (pbdev->pci_group->zpci_group.fr & CLP_RSP_QPCIG_MASK_RELAXED) {
+                ret = s390_pci_get_zpci_io_region(pbdev);
+            }
+            if (ret) {
+                error_setg(errp, "vfio zPCI I/O region support is mandatory "
+                           "for %02x:%02x.%01x", pci_dev_bus_num(pdev),
+                           PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
+            }
         } else {
             pbdev->fh |= FH_SHM_EMUL;
 
diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
index 30698e5..d4c79f6 100644
--- a/hw/s390x/s390-pci-inst.c
+++ b/hw/s390x/s390-pci-inst.c
@@ -19,6 +19,7 @@
 #include "sysemu/hw_accel.h"
 #include "hw/s390x/s390-pci-inst.h"
 #include "hw/s390x/s390-pci-bus.h"
+#include "hw/s390x/s390-pci-vfio.h"
 #include "hw/s390x/tod.h"
 
 #ifndef DEBUG_S390PCI_INST
@@ -897,6 +898,8 @@ int pcistb_service_call(S390CPU *cpu, uint8_t r1, uint8_t r3, uint64_t gaddr,
     ret = pbdev->ops.pcistb(pbdev, cpu, gaddr, ar, pcias, len, offset);
 
     switch (ret) {
+    case -EIO:
+        /* fall through */
     case -EINVAL:
         s390_program_interrupt(env, PGM_OPERAND, ra);
         return 0;
@@ -1386,3 +1389,8 @@ void zpci_assign_default_ops(S390PCIBusDevice *pbdev)
     pbdev->ops.pcilg = pcilg_default;
     pbdev->ops.pcistb = pcistb_default;
 }
+
+void zpci_assign_ops_vfio_io_region(S390PCIBusDevice *pbdev)
+{
+    pbdev->ops.pcistb = s390_pci_vfio_pcistb;
+}
diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
index 9439fe1..ad50a62 100644
--- a/hw/s390x/s390-pci-vfio.c
+++ b/hw/s390x/s390-pci-vfio.c
@@ -17,6 +17,7 @@
 #include "trace.h"
 #include "hw/s390x/s390-pci-bus.h"
 #include "hw/s390x/s390-pci-clp.h"
+#include "hw/s390x/s390-pci-inst.h"
 #include "hw/s390x/s390-pci-vfio.h"
 #include "hw/vfio/pci.h"
 #include "hw/vfio/vfio-common.h"
@@ -277,3 +278,110 @@ retry:
 
     return;
 }
+
+/*
+ * This function will look for the VFIO_REGION_SUBTYPE_IBM_ZPCI_IO vfio
+ * device region, which is used for performing block I/O operations.
+ */
+int s390_pci_get_zpci_io_region(S390PCIBusDevice *pbdev)
+{
+    VFIOPCIDevice *vfio_pci;
+    VFIODevice *vdev;
+    struct vfio_region_info *info;
+    int ret;
+
+    vfio_pci = container_of(pbdev->pdev, VFIOPCIDevice, pdev);
+    vdev = &vfio_pci->vbasedev;
+
+    if (vdev->num_regions < VFIO_PCI_NUM_REGIONS + 1) {
+        return -ENOENT;
+    }
+
+    /* Get the I/O region if it's available */
+    if (vfio_get_dev_region_info(vdev,
+                                 PCI_VENDOR_ID_IBM |
+                                 VFIO_REGION_TYPE_PCI_VENDOR_TYPE,
+                                 VFIO_REGION_SUBTYPE_IBM_ZPCI_IO, &info)) {
+        return -ENOENT;
+    }
+
+    /* If the size is unexpectedly small, don't use the region */
+    if (sizeof(*pbdev->io_region) > info->size) {
+        return -EINVAL;
+    }
+
+    pbdev->io_region = g_malloc0(info->size);
+
+    /* Check the header for setup information */
+    ret = pread(vfio_pci->vbasedev.fd, &pbdev->io_region->hdr,
+                sizeof(struct vfio_zpci_io_hdr), info->offset);
+    if (ret != sizeof(struct vfio_zpci_io_hdr)) {
+        g_free(pbdev->io_region);
+        pbdev->io_region = 0;
+        ret = -EINVAL;
+    } else {
+        pbdev->io_region_op_offset = info->offset +
+                                     offsetof(struct vfio_region_zpci_io, req);
+        /* All devices in this group will use the I/O region for PCISTB */
+        pbdev->pci_group->zpci_group.maxstbl = MIN(PAGE_SIZE,
+                                               pbdev->io_region->hdr.max);
+        ret = 0;
+    }
+    g_free(info);
+
+    /* Register the new handlers for the device if region available */
+    if (pbdev->io_region) {
+        zpci_assign_ops_vfio_io_region(pbdev);
+    }
+
+    return ret;
+}
+
+int s390_pci_vfio_pcistb(S390PCIBusDevice *pbdev, S390CPU *cpu, uint64_t gaddr,
+                         uint8_t ar, uint8_t pcias, uint16_t len,
+                         uint64_t offset)
+{
+    struct vfio_region_zpci_io *region = pbdev->io_region;
+    VFIOPCIDevice *vfio_pci;
+    uint8_t *buffer;
+    int ret;
+
+    if (region == NULL) {
+        return -EIO;
+    }
+
+    vfio_pci = container_of(pbdev->pdev, VFIOPCIDevice, pdev);
+
+    /*
+     * We've already ensured the input can be no larger than a page.  PCISTB
+     * requires that the operation payload does not cross a page boundary,
+     * otherwise the operation will be rejected.  Therefore, just get a single
+     * page for the write.
+     */
+    buffer = qemu_memalign(PAGE_SIZE, PAGE_SIZE);
+
+    if (s390_cpu_virt_mem_read(cpu, gaddr, ar, buffer, len)) {
+        ret = -EACCES;
+        goto out;
+    }
+
+    region->req.gaddr = (uint64_t)buffer;
+    region->req.offset = offset;
+    region->req.len = len;
+    region->req.pcias = pcias;
+    region->req.flags = VFIO_ZPCI_IO_FLAG_BLOCKW;
+
+    ret = pwrite(vfio_pci->vbasedev.fd, &region->req,
+                 sizeof(struct vfio_zpci_io_req),
+                 pbdev->io_region_op_offset);
+    if (ret != sizeof(struct vfio_zpci_io_req)) {
+        ret = -EIO;
+    } else {
+        ret = 0;
+    }
+
+out:
+    qemu_vfree(buffer);
+
+    return ret;
+}
diff --git a/include/hw/s390x/s390-pci-bus.h b/include/hw/s390x/s390-pci-bus.h
index bf0034f..8986a5f 100644
--- a/include/hw/s390x/s390-pci-bus.h
+++ b/include/hw/s390x/s390-pci-bus.h
@@ -355,6 +355,8 @@ struct S390PCIBusDevice {
     uint32_t fh;
     uint32_t fid;
     bool fid_defined;
+    uint64_t io_region_op_offset;
+    struct vfio_region_zpci_io *io_region;
     uint64_t fmb_addr;
     ZpciFmb fmb;
     QEMUTimer *fmb_timer;
diff --git a/include/hw/s390x/s390-pci-inst.h b/include/hw/s390x/s390-pci-inst.h
index c9fe3f1..7ed6175 100644
--- a/include/hw/s390x/s390-pci-inst.h
+++ b/include/hw/s390x/s390-pci-inst.h
@@ -112,6 +112,7 @@ int stpcifc_service_call(S390CPU *cpu, uint8_t r1, uint64_t fiba, uint8_t ar,
                          uintptr_t ra);
 void fmb_timer_free(S390PCIBusDevice *pbdev);
 void zpci_assign_default_ops(S390PCIBusDevice *pbdev);
+void zpci_assign_ops_vfio_io_region(S390PCIBusDevice *pbdev);
 
 #define ZPCI_IO_BAR_MIN 0
 #define ZPCI_IO_BAR_MAX 5
diff --git a/include/hw/s390x/s390-pci-vfio.h b/include/hw/s390x/s390-pci-vfio.h
index ff708ae..f0a994f 100644
--- a/include/hw/s390x/s390-pci-vfio.h
+++ b/include/hw/s390x/s390-pci-vfio.h
@@ -21,6 +21,10 @@ S390PCIDMACount *s390_pci_start_dma_count(S390pciState *s,
                                           S390PCIBusDevice *pbdev);
 void s390_pci_end_dma_count(S390pciState *s, S390PCIDMACount *cnt);
 void s390_pci_get_clp_info(S390PCIBusDevice *pbdev);
+int s390_pci_get_zpci_io_region(S390PCIBusDevice *pbdev);
+int s390_pci_vfio_pcistb(S390PCIBusDevice *pbdev, S390CPU *cpu, uint64_t gaddr,
+                         uint8_t ar, uint8_t pcias, uint16_t len,
+                         uint64_t offset);
 #else
 static inline bool s390_pci_update_dma_avail(int fd, unsigned int *avail)
 {
@@ -34,6 +38,17 @@ static inline S390PCIDMACount *s390_pci_start_dma_count(S390pciState *s,
 static inline void s390_pci_end_dma_count(S390pciState *s,
                                           S390PCIDMACount *cnt) { }
 static inline void s390_pci_get_clp_info(S390PCIBusDevice *pbdev) { }
+static inline int s390_pci_get_zpci_io_region(S390PCIBusDevice *pbdev)
+{
+    return -EINVAL;
+}
+static inline int s390_pci_vfio_pcistb(S390PCIBusDevice *pbdev, S390CPU *cpu,
+                                       uint64_t gaddr, uint8_t ar,
+                                       uint8_t pcias, uint16_t len,
+                                       uint64_t offset)
+{
+    return -EIO;
+}
 #endif
 
 #endif
