Merge tag 'mem-2023-07-12' of https://github.com/davidhildenbrand/qemu into staging

Hi,

"Host Memory Backends" and "Memory devices" queue ("mem"):
- Memory device cleanups (especially around machine initialization)
- "x-ignore-shared" migration support for virtio-mem
- Add an abstract virtio-md-pci device as a common parent for
  virtio-mem-pci and virtio-pmem-pci (virtio based memory devices)
- Device unplug support for virtio-mem-pci

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# gpg: Signature made Wed 12 Jul 2023 09:10:44 AM BST
# gpg:                using RSA key 1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A
# gpg:                issuer "david@redhat.com"
# gpg: Good signature from "David Hildenbrand <david@redhat.com>" [unknown]
# gpg:                 aka "David Hildenbrand <davidhildenbrand@gmail.com>" [undefined]
# gpg:                 aka "David Hildenbrand <hildenbr@in.tum.de>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 1BD9 CAAD 735C 4C3A 460D  FCCA 4DDE 10F7 00FF 835A

* tag 'mem-2023-07-12' of https://github.com/davidhildenbrand/qemu: (21 commits)
  virtio-mem-pci: Device unplug support
  virtio-mem: Prepare for device unplug support
  virtio-md-pci: Support unplug requests for compatible devices
  virtio-md-pci: Handle unplug of virtio based memory devices
  arm/virt: Use virtio-md-pci (un)plug functions
  pc: Factor out (un)plug handling of virtio-md-pci devices
  virtio-md-pci: New parent type for virtio-mem-pci and virtio-pmem-pci
  virtio-mem: Support "x-ignore-shared" migration
  migration/ram: Expose ramblock_is_ignored() as migrate_ram_is_ignored()
  virtio-mem: Skip most of virtio_mem_unplug_all() without plugged memory
  softmmu/physmem: Warn with ram_block_discard_range() on MAP_PRIVATE file mapping
  memory-device: Track used region size in DeviceMemoryState
  memory-device: Refactor memory_device_pre_plug()
  hw/i386/pc: Remove PC_MACHINE_DEVMEM_REGION_SIZE
  hw/i386/acpi-build: Rely on machine->device_memory when building SRAT
  hw/i386/pc: Use machine_memory_devices_init()
  hw/loongarch/virt: Use machine_memory_devices_init()
  hw/ppc/spapr: Use machine_memory_devices_init()
  hw/arm/virt: Use machine_memory_devices_init()
  memory-device: Introduce machine_memory_devices_init()
  ...

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

27 files changed, 479 insertions, 308 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index e158a25..12e59b6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2229,6 +2229,13 @@ F: hw/virtio/virtio-crypto.c
 F: hw/virtio/virtio-crypto-pci.c
 F: include/hw/virtio/virtio-crypto.h
 
+virtio based memory device
+M: David Hildenbrand <david@redhat.com>
+S: Supported
+F: hw/virtio/virtio-md-pci.c
+F: include/hw/virtio/virtio-md-pci.h
+F: stubs/virtio-md-pci.c
+
 virtio-mem
 M: David Hildenbrand <david@redhat.com>
 S: Supported
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 8a4c663..7d9dbc2 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -73,11 +73,10 @@
 #include "hw/arm/smmuv3.h"
 #include "hw/acpi/acpi.h"
 #include "target/arm/internals.h"
-#include "hw/mem/memory-device.h"
 #include "hw/mem/pc-dimm.h"
 #include "hw/mem/nvdimm.h"
 #include "hw/acpi/generic_event_device.h"
-#include "hw/virtio/virtio-mem-pci.h"
+#include "hw/virtio/virtio-md-pci.h"
 #include "hw/virtio/virtio-iommu.h"
 #include "hw/char/pl011.h"
 #include "qemu/guest-random.h"
@@ -1813,10 +1812,7 @@ static void virt_set_memmap(VirtMachineState *vms, int pa_bits)
     virt_set_high_memmap(vms, base, pa_bits);
 
     if (device_memory_size > 0) {
-        ms->device_memory = g_malloc0(sizeof(*ms->device_memory));
-        ms->device_memory->base = device_memory_base;
-        memory_region_init(&ms->device_memory->mr, OBJECT(vms),
-                           "device-memory", device_memory_size);
+        machine_memory_devices_init(ms, device_memory_base, device_memory_size);
     }
 }
 
@@ -2257,10 +2253,6 @@ static void machvirt_init(MachineState *machine)
 
     memory_region_add_subregion(sysmem, vms->memmap[VIRT_MEM].base,
                                 machine->ram);
-    if (machine->device_memory) {
-        memory_region_add_subregion(sysmem, machine->device_memory->base,
-                                    &machine->device_memory->mr);
-    }
 
     virt_flash_fdt(vms, sysmem, secure_sysmem ?: sysmem);
 
@@ -2740,64 +2732,6 @@ static void virt_memory_plug(HotplugHandler *hotplug_dev,
                          dev, &error_abort);
 }
 
-static void virt_virtio_md_pci_pre_plug(HotplugHandler *hotplug_dev,
-                                        DeviceState *dev, Error **errp)
-{
-    HotplugHandler *hotplug_dev2 = qdev_get_bus_hotplug_handler(dev);
-    Error *local_err = NULL;
-
-    if (!hotplug_dev2 && dev->hotplugged) {
-        /*
-         * Without a bus hotplug handler, we cannot control the plug/unplug
-         * order. We should never reach this point when hotplugging on ARM.
-         * However, it's nice to add a safety net, similar to what we have
-         * on x86.
-         */
-        error_setg(errp, "hotplug of virtio based memory devices not supported"
-                   " on this bus.");
-        return;
-    }
-    /*
-     * First, see if we can plug this memory device at all. If that
-     * succeeds, branch of to the actual hotplug handler.
-     */
-    memory_device_pre_plug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev), NULL,
-                           &local_err);
-    if (!local_err && hotplug_dev2) {
-        hotplug_handler_pre_plug(hotplug_dev2, dev, &local_err);
-    }
-    error_propagate(errp, local_err);
-}
-
-static void virt_virtio_md_pci_plug(HotplugHandler *hotplug_dev,
-                                    DeviceState *dev, Error **errp)
-{
-    HotplugHandler *hotplug_dev2 = qdev_get_bus_hotplug_handler(dev);
-    Error *local_err = NULL;
-
-    /*
-     * Plug the memory device first and then branch off to the actual
-     * hotplug handler. If that one fails, we can easily undo the memory
-     * device bits.
-     */
-    memory_device_plug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev));
-    if (hotplug_dev2) {
-        hotplug_handler_plug(hotplug_dev2, dev, &local_err);
-        if (local_err) {
-            memory_device_unplug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev));
-        }
-    }
-    error_propagate(errp, local_err);
-}
-
-static void virt_virtio_md_pci_unplug_request(HotplugHandler *hotplug_dev,
-                                              DeviceState *dev, Error **errp)
-{
-    /* We don't support hot unplug of virtio based memory devices */
-    error_setg(errp, "virtio based memory devices cannot be unplugged.");
-}
-
-
 static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
                                             DeviceState *dev, Error **errp)
 {
@@ -2805,8 +2739,8 @@ static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
         virt_memory_pre_plug(hotplug_dev, dev, errp);
-    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        virt_virtio_md_pci_pre_plug(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_pre_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
         hwaddr db_start = 0, db_end = 0;
         char *resv_prop_str;
@@ -2855,12 +2789,11 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
                                      SYS_BUS_DEVICE(dev));
         }
     }
+
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
         virt_memory_plug(hotplug_dev, dev, errp);
-    }
-
-    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        virt_virtio_md_pci_plug(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
     }
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
@@ -2915,8 +2848,9 @@ static void virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
 {
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
         virt_dimm_unplug_request(hotplug_dev, dev, errp);
-    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        virt_virtio_md_pci_unplug_request(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_unplug_request(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev),
+                                     errp);
     } else {
         error_setg(errp, "device unplug request for unsupported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
@@ -2928,6 +2862,8 @@ static void virt_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
 {
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
         virt_dimm_unplug(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_unplug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
     } else {
         error_setg(errp, "virt: device unplug for unsupported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
@@ -2941,7 +2877,7 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
 
     if (device_is_dynamic_sysbus(mc, dev) ||
         object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) ||
-        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI) ||
+        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI) ||
         object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
         return HOTPLUG_HANDLER(machine);
     }
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 5121620..9c74fa1 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1950,12 +1950,8 @@ build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
     MachineClass *mc = MACHINE_GET_CLASS(machine);
     X86MachineState *x86ms = X86_MACHINE(machine);
     const CPUArchIdList *apic_ids = mc->possible_cpu_arch_ids(machine);
-    PCMachineState *pcms = PC_MACHINE(machine);
     int nb_numa_nodes = machine->numa_state->num_nodes;
     NodeInfo *numa_info = machine->numa_state->nodes;
-    ram_addr_t hotpluggable_address_space_size =
-        object_property_get_int(OBJECT(pcms), PC_MACHINE_DEVMEM_REGION_SIZE,
-                                NULL);
     AcpiTable table = { .sig = "SRAT", .rev = 1, .oem_id = x86ms->oem_id,
                         .oem_table_id = x86ms->oem_table_id };
 
@@ -2071,9 +2067,10 @@ build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
      * Memory devices may override proximity set by this entry,
      * providing _PXM method if necessary.
      */
-    if (hotpluggable_address_space_size) {
+    if (machine->device_memory) {
         build_srat_memory(table_data, machine->device_memory->base,
-                          hotpluggable_address_space_size, nb_numa_nodes - 1,
+                          memory_region_size(&machine->device_memory->mr),
+                          nb_numa_nodes - 1,
                           MEM_AFFINITY_HOTPLUGGABLE | MEM_AFFINITY_ENABLED);
     }
 
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index f01d7de..3109d5e 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -88,13 +88,11 @@
 #include "hw/net/ne2000-isa.h"
 #include "standard-headers/asm-x86/bootparam.h"
 #include "hw/virtio/virtio-iommu.h"
-#include "hw/virtio/virtio-pmem-pci.h"
-#include "hw/virtio/virtio-mem-pci.h"
+#include "hw/virtio/virtio-md-pci.h"
 #include "hw/i386/kvm/xen_overlay.h"
 #include "hw/i386/kvm/xen_evtchn.h"
 #include "hw/i386/kvm/xen_gnttab.h"
 #include "hw/i386/kvm/xen_xenstore.h"
-#include "hw/mem/memory-device.h"
 #include "sysemu/replay.h"
 #include "target/i386/cpu.h"
 #include "e820_memory_layout.h"
@@ -1039,13 +1037,11 @@ void pc_memory_init(PCMachineState *pcms,
         exit(EXIT_FAILURE);
     }
 
-    /* always allocate the device memory information */
-    machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
-
     /* initialize device memory address space */
     if (pcmc->has_reserved_memory &&
         (machine->ram_size < machine->maxram_size)) {
         ram_addr_t device_mem_size;
+        hwaddr device_mem_base;
 
         if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
             error_report("unsupported amount of memory slots: %"PRIu64,
@@ -1060,19 +1056,14 @@ void pc_memory_init(PCMachineState *pcms,
             exit(EXIT_FAILURE);
         }
 
-        pc_get_device_memory_range(pcms, &machine->device_memory->base, &device_mem_size);
+        pc_get_device_memory_range(pcms, &device_mem_base, &device_mem_size);
 
-        if ((machine->device_memory->base + device_mem_size) <
-            device_mem_size) {
+        if (device_mem_base + device_mem_size < device_mem_size) {
             error_report("unsupported amount of maximum memory: " RAM_ADDR_FMT,
                          machine->maxram_size);
             exit(EXIT_FAILURE);
         }
-
-        memory_region_init(&machine->device_memory->mr, OBJECT(pcms),
-                           "device-memory", device_mem_size);
-        memory_region_add_subregion(system_memory, machine->device_memory->base,
-                                    &machine->device_memory->mr);
+        machine_memory_devices_init(machine, device_mem_base, device_mem_size);
     }
 
     if (pcms->cxl_devices_state.is_enabled) {
@@ -1120,7 +1111,7 @@ void pc_memory_init(PCMachineState *pcms,
 
     rom_set_fw(fw_cfg);
 
-    if (pcmc->has_reserved_memory && machine->device_memory->base) {
+    if (machine->device_memory) {
         uint64_t *val = g_malloc(sizeof(*val));
         PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
         uint64_t res_mem_end = machine->device_memory->base;
@@ -1500,68 +1491,6 @@ static void pc_memory_unplug(HotplugHandler *hotplug_dev,
     error_propagate(errp, local_err);
 }
 
-static void pc_virtio_md_pci_pre_plug(HotplugHandler *hotplug_dev,
-                                      DeviceState *dev, Error **errp)
-{
-    HotplugHandler *hotplug_dev2 = qdev_get_bus_hotplug_handler(dev);
-    Error *local_err = NULL;
-
-    if (!hotplug_dev2 && dev->hotplugged) {
-        /*
-         * Without a bus hotplug handler, we cannot control the plug/unplug
-         * order. We should never reach this point when hotplugging on x86,
-         * however, better add a safety net.
-         */
-        error_setg(errp, "hotplug of virtio based memory devices not supported"
-                   " on this bus.");
-        return;
-    }
-    /*
-     * First, see if we can plug this memory device at all. If that
-     * succeeds, branch of to the actual hotplug handler.
-     */
-    memory_device_pre_plug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev), NULL,
-                           &local_err);
-    if (!local_err && hotplug_dev2) {
-        hotplug_handler_pre_plug(hotplug_dev2, dev, &local_err);
-    }
-    error_propagate(errp, local_err);
-}
-
-static void pc_virtio_md_pci_plug(HotplugHandler *hotplug_dev,
-                                  DeviceState *dev, Error **errp)
-{
-    HotplugHandler *hotplug_dev2 = qdev_get_bus_hotplug_handler(dev);
-    Error *local_err = NULL;
-
-    /*
-     * Plug the memory device first and then branch off to the actual
-     * hotplug handler. If that one fails, we can easily undo the memory
-     * device bits.
-     */
-    memory_device_plug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev));
-    if (hotplug_dev2) {
-        hotplug_handler_plug(hotplug_dev2, dev, &local_err);
-        if (local_err) {
-            memory_device_unplug(MEMORY_DEVICE(dev), MACHINE(hotplug_dev));
-        }
-    }
-    error_propagate(errp, local_err);
-}
-
-static void pc_virtio_md_pci_unplug_request(HotplugHandler *hotplug_dev,
-                                            DeviceState *dev, Error **errp)
-{
-    /* We don't support hot unplug of virtio based memory devices */
-    error_setg(errp, "virtio based memory devices cannot be unplugged.");
-}
-
-static void pc_virtio_md_pci_unplug(HotplugHandler *hotplug_dev,
-                                    DeviceState *dev, Error **errp)
-{
-    /* We don't support hot unplug of virtio based memory devices */
-}
-
 static void pc_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
                                           DeviceState *dev, Error **errp)
 {
@@ -1569,9 +1498,8 @@ static void pc_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
         pc_memory_pre_plug(hotplug_dev, dev, errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
         x86_cpu_pre_plug(hotplug_dev, dev, errp);
-    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
-               object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        pc_virtio_md_pci_pre_plug(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_pre_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
         /* Declare the APIC range as the reserved MSI region */
         char *resv_prop_str = g_strdup_printf("0xfee00000:0xfeefffff:%d",
@@ -1603,9 +1531,8 @@ static void pc_machine_device_plug_cb(HotplugHandler *hotplug_dev,
         pc_memory_plug(hotplug_dev, dev, errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
         x86_cpu_plug(hotplug_dev, dev, errp);
-    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
-               object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        pc_virtio_md_pci_plug(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
     }
 }
 
@@ -1616,9 +1543,9 @@ static void pc_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
         pc_memory_unplug_request(hotplug_dev, dev, errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
         x86_cpu_unplug_request_cb(hotplug_dev, dev, errp);
-    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
-               object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        pc_virtio_md_pci_unplug_request(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_unplug_request(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev),
+                                     errp);
     } else {
         error_setg(errp, "acpi: device unplug request for not supported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
@@ -1632,9 +1559,8 @@ static void pc_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
         pc_memory_unplug(hotplug_dev, dev, errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
         x86_cpu_unplug_cb(hotplug_dev, dev, errp);
-    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
-               object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI)) {
-        pc_virtio_md_pci_unplug(hotplug_dev, dev, errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_unplug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
     } else {
         error_setg(errp, "acpi: device unplug for not supported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
@@ -1646,8 +1572,7 @@ static HotplugHandler *pc_get_hotplug_handler(MachineState *machine,
 {
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) ||
         object_dynamic_cast(OBJECT(dev), TYPE_CPU) ||
-        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_PMEM_PCI) ||
-        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MEM_PCI) ||
+        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI) ||
         object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI) ||
         object_dynamic_cast(OBJECT(dev), TYPE_X86_IOMMU_DEVICE)) {
         return HOTPLUG_HANDLER(machine);
@@ -1656,21 +1581,6 @@ static HotplugHandler *pc_get_hotplug_handler(MachineState *machine,
     return NULL;
 }
 
-static void
-pc_machine_get_device_memory_region_size(Object *obj, Visitor *v,
-                                         const char *name, void *opaque,
-                                         Error **errp)
-{
-    MachineState *ms = MACHINE(obj);
-    int64_t value = 0;
-
-    if (ms->device_memory) {
-        value = memory_region_size(&ms->device_memory->mr);
-    }
-
-    visit_type_int(v, name, &value, errp);
-}
-
 static void pc_machine_get_vmport(Object *obj, Visitor *v, const char *name,
                                   void *opaque, Error **errp)
 {
@@ -1984,10 +1894,6 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     object_class_property_set_description(oc, PC_MACHINE_MAX_RAM_BELOW_4G,
         "Maximum ram below the 4G boundary (32bit boundary)");
 
-    object_class_property_add(oc, PC_MACHINE_DEVMEM_REGION_SIZE, "int",
-        pc_machine_get_device_memory_region_size, NULL,
-        NULL, NULL);
-
     object_class_property_add(oc, PC_MACHINE_VMPORT, "OnOffAuto",
         pc_machine_get_vmport, pc_machine_set_vmport,
         NULL, NULL);
diff --git a/hw/loongarch/virt.c b/hw/loongarch/virt.c
index 51a453f..e19b042 100644
--- a/hw/loongarch/virt.c
+++ b/hw/loongarch/virt.c
@@ -857,8 +857,8 @@ static void loongarch_init(MachineState *machine)
 
     /* initialize device memory address space */
     if (machine->ram_size < machine->maxram_size) {
-        machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
         ram_addr_t device_mem_size = machine->maxram_size - machine->ram_size;
+        hwaddr device_mem_base;
 
         if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
             error_report("unsupported amount of memory slots: %"PRIu64,
@@ -873,14 +873,8 @@ static void loongarch_init(MachineState *machine)
             exit(EXIT_FAILURE);
         }
         /* device memory base is the top of high memory address. */
-        machine->device_memory->base = 0x90000000 + highram_size;
-        machine->device_memory->base =
-            ROUND_UP(machine->device_memory->base, 1 * GiB);
-
-        memory_region_init(&machine->device_memory->mr, OBJECT(lams),
-                           "device-memory", device_mem_size);
-        memory_region_add_subregion(address_space_mem, machine->device_memory->base,
-                                    &machine->device_memory->mr);
+        device_mem_base = ROUND_UP(VIRT_HIGHMEM_BASE + highram_size, 1 * GiB);
+        machine_memory_devices_init(machine, device_mem_base, device_mem_size);
     }
 
     /* Add isa io region */
diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
index 1636db9..667d56b 100644
--- a/hw/mem/memory-device.c
+++ b/hw/mem/memory-device.c
@@ -17,6 +17,7 @@
 #include "qemu/range.h"
 #include "hw/virtio/vhost.h"
 #include "sysemu/kvm.h"
+#include "exec/address-spaces.h"
 #include "trace.h"
 
 static gint memory_device_addr_sort(gconstpointer a, gconstpointer b)
@@ -51,27 +52,11 @@ static int memory_device_build_list(Object *obj, void *opaque)
     return 0;
 }
 
-static int memory_device_used_region_size(Object *obj, void *opaque)
-{
-    uint64_t *size = opaque;
-
-    if (object_dynamic_cast(obj, TYPE_MEMORY_DEVICE)) {
-        const DeviceState *dev = DEVICE(obj);
-        const MemoryDeviceState *md = MEMORY_DEVICE(obj);
-
-        if (dev->realized) {
-            *size += memory_device_get_region_size(md, &error_abort);
-        }
-    }
-
-    object_child_foreach(obj, memory_device_used_region_size, opaque);
-    return 0;
-}
-
-static void memory_device_check_addable(MachineState *ms, uint64_t size,
+static void memory_device_check_addable(MachineState *ms, MemoryRegion *mr,
                                         Error **errp)
 {
-    uint64_t used_region_size = 0;
+    const uint64_t used_region_size = ms->device_memory->used_region_size;
+    const uint64_t size = memory_region_size(mr);
 
     /* we will need a new memory slot for kvm and vhost */
     if (kvm_enabled() && !kvm_has_free_slot(ms)) {
@@ -84,7 +69,6 @@ static void memory_device_check_addable(MachineState *ms, uint64_t size,
     }
 
     /* will we exceed the total amount of memory specified */
-    memory_device_used_region_size(OBJECT(ms), &used_region_size);
     if (used_region_size + size < used_region_size ||
         used_region_size + size > ms->maxram_size - ms->ram_size) {
         error_setg(errp, "not enough space, currently 0x%" PRIx64
@@ -100,21 +84,9 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
                                             uint64_t align, uint64_t size,
                                             Error **errp)
 {
-    Error *err = NULL;
     GSList *list = NULL, *item;
     Range as, new = range_empty;
 
-    if (!ms->device_memory) {
-        error_setg(errp, "memory devices (e.g. for memory hotplug) are not "
-                         "supported by the machine");
-        return 0;
-    }
-
-    if (!memory_region_size(&ms->device_memory->mr)) {
-        error_setg(errp, "memory devices (e.g. for memory hotplug) are not "
-                         "enabled, please specify the maxmem option");
-        return 0;
-    }
     range_init_nofail(&as, ms->device_memory->base,
                       memory_region_size(&ms->device_memory->mr));
 
@@ -126,12 +98,6 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
                     align);
     }
 
-    memory_device_check_addable(ms, size, &err);
-    if (err) {
-        error_propagate(errp, err);
-        return 0;
-    }
-
     if (hint && !QEMU_IS_ALIGNED(*hint, align)) {
         error_setg(errp, "address must be aligned to 0x%" PRIx64 " bytes",
                    align);
@@ -255,11 +221,23 @@ void memory_device_pre_plug(MemoryDeviceState *md, MachineState *ms,
     uint64_t addr, align = 0;
     MemoryRegion *mr;
 
+    if (!ms->device_memory) {
+        error_setg(errp, "the configuration is not prepared for memory devices"
+                         " (e.g., for memory hotplug), consider specifying the"
+                         " maxmem option");
+        return;
+    }
+
     mr = mdc->get_memory_region(md, &local_err);
     if (local_err) {
         goto out;
     }
 
+    memory_device_check_addable(ms, mr, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
     if (legacy_align) {
         align = *legacy_align;
     } else {
@@ -296,6 +274,7 @@ void memory_device_plug(MemoryDeviceState *md, MachineState *ms)
     mr = mdc->get_memory_region(md, &error_abort);
     g_assert(ms->device_memory);
 
+    ms->device_memory->used_region_size += memory_region_size(mr);
     memory_region_add_subregion(&ms->device_memory->mr,
                                 addr - ms->device_memory->base, mr);
     trace_memory_device_plug(DEVICE(md)->id ? DEVICE(md)->id : "", addr);
@@ -314,6 +293,7 @@ void memory_device_unplug(MemoryDeviceState *md, MachineState *ms)
     g_assert(ms->device_memory);
 
     memory_region_del_subregion(&ms->device_memory->mr, mr);
+    ms->device_memory->used_region_size -= memory_region_size(mr);
     trace_memory_device_unplug(DEVICE(md)->id ? DEVICE(md)->id : "",
                                mdc->get_addr(md));
 }
@@ -333,6 +313,19 @@ uint64_t memory_device_get_region_size(const MemoryDeviceState *md,
     return memory_region_size(mr);
 }
 
+void machine_memory_devices_init(MachineState *ms, hwaddr base, uint64_t size)
+{
+    g_assert(size);
+    g_assert(!ms->device_memory);
+    ms->device_memory = g_new0(DeviceMemoryState, 1);
+    ms->device_memory->base = base;
+
+    memory_region_init(&ms->device_memory->mr, OBJECT(ms), "device-memory",
+                       size);
+    memory_region_add_subregion(get_system_memory(), ms->device_memory->base,
+                                &ms->device_memory->mr);
+}
+
 static const TypeInfo memory_device_info = {
     .name          = TYPE_MEMORY_DEVICE,
     .parent        = TYPE_INTERFACE,
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 54dbfd7..1c8b8d5 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -547,10 +547,8 @@ static int spapr_dt_dynamic_reconfiguration_memory(SpaprMachineState *spapr,
                                 cpu_to_be32(lmb_size & 0xffffffff)};
     MemoryDeviceInfoList *dimms = NULL;
 
-    /*
-     * Don't create the node if there is no device memory
-     */
-    if (machine->ram_size == machine->maxram_size) {
+    /* Don't create the node if there is no device memory. */
+    if (!machine->device_memory) {
         return 0;
     }
 
@@ -860,16 +858,23 @@ static void spapr_dt_rtas(SpaprMachineState *spapr, void *fdt)
     int rtas;
     GString *hypertas = g_string_sized_new(256);
     GString *qemu_hypertas = g_string_sized_new(256);
-    uint64_t max_device_addr = MACHINE(spapr)->device_memory->base +
-        memory_region_size(&MACHINE(spapr)->device_memory->mr);
     uint32_t lrdr_capacity[] = {
-        cpu_to_be32(max_device_addr >> 32),
-        cpu_to_be32(max_device_addr & 0xffffffff),
+        0,
+        0,
         cpu_to_be32(SPAPR_MEMORY_BLOCK_SIZE >> 32),
         cpu_to_be32(SPAPR_MEMORY_BLOCK_SIZE & 0xffffffff),
         cpu_to_be32(ms->smp.max_cpus / ms->smp.threads),
     };
 
+    /* Do we have device memory? */
+    if (MACHINE(spapr)->device_memory) {
+        uint64_t max_device_addr = MACHINE(spapr)->device_memory->base +
+            memory_region_size(&MACHINE(spapr)->device_memory->mr);
+
+        lrdr_capacity[0] = cpu_to_be32(max_device_addr >> 32);
+        lrdr_capacity[1] = cpu_to_be32(max_device_addr & 0xffffffff);
+    }
+
     _FDT(rtas = fdt_add_subnode(fdt, 0, "rtas"));
 
     /* hypertas */
@@ -2455,6 +2460,7 @@ static void spapr_create_lmb_dr_connectors(SpaprMachineState *spapr)
     uint32_t nr_lmbs = (machine->maxram_size - machine->ram_size)/lmb_size;
     int i;
 
+    g_assert(!nr_lmbs || machine->device_memory);
     for (i = 0; i < nr_lmbs; i++) {
         uint64_t addr;
 
@@ -2876,12 +2882,11 @@ static void spapr_machine_init(MachineState *machine)
     /* map RAM */
     memory_region_add_subregion(sysmem, 0, machine->ram);
 
-    /* always allocate the device memory information */
-    machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
-
     /* initialize hotplug memory address space */
     if (machine->ram_size < machine->maxram_size) {
         ram_addr_t device_mem_size = machine->maxram_size - machine->ram_size;
+        hwaddr device_mem_base;
+
         /*
          * Limit the number of hotpluggable memory slots to half the number
          * slots that KVM supports, leaving the other half for PCI and other
@@ -2900,12 +2905,8 @@ static void spapr_machine_init(MachineState *machine)
             exit(1);
         }
 
-        machine->device_memory->base = ROUND_UP(machine->ram_size,
-                                                SPAPR_DEVICE_MEM_ALIGN);
-        memory_region_init(&machine->device_memory->mr, OBJECT(spapr),
-                           "device-memory", device_mem_size);
-        memory_region_add_subregion(sysmem, machine->device_memory->base,
-                                    &machine->device_memory->mr);
+        device_mem_base = ROUND_UP(machine->ram_size, SPAPR_DEVICE_MEM_ALIGN);
+        machine_memory_devices_init(machine, device_mem_base, device_mem_size);
     }
 
     if (smc->dr_lmb_enabled) {
@@ -5119,7 +5120,7 @@ static bool phb_placement_2_7(SpaprMachineState *spapr, uint32_t index,
     int i;
 
     /* Do we have device memory? */
-    if (MACHINE(spapr)->maxram_size > ram_top) {
+    if (MACHINE(spapr)->device_memory) {
         /* Can't just use maxram_size, because there may be an
          * alignment gap between normal and device memory regions
          */
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 002ea0b..9b1f225 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -32,7 +32,7 @@ bool is_ram_address(SpaprMachineState *spapr, hwaddr addr)
     if (addr < machine->ram_size) {
         return true;
     }
-    if ((addr >= dms->base)
+    if (dms && (addr >= dms->base)
         && ((addr - dms->base) < memory_region_size(&dms->mr))) {
         return true;
     }
diff --git a/hw/virtio/Kconfig b/hw/virtio/Kconfig
index a9ee090..92c9cf6 100644
--- a/hw/virtio/Kconfig
+++ b/hw/virtio/Kconfig
@@ -35,6 +35,10 @@ config VIRTIO_CRYPTO
     default y
     depends on VIRTIO
 
+config VIRTIO_MD
+    bool
+    select MEM_DEVICE
+
 config VIRTIO_PMEM_SUPPORTED
     bool
 
@@ -43,7 +47,7 @@ config VIRTIO_PMEM
     default y
     depends on VIRTIO
     depends on VIRTIO_PMEM_SUPPORTED
-    select MEM_DEVICE
+    select VIRTIO_MD
 
 config VIRTIO_MEM_SUPPORTED
     bool
@@ -54,7 +58,7 @@ config VIRTIO_MEM
     depends on VIRTIO
     depends on LINUX
     depends on VIRTIO_MEM_SUPPORTED
-    select MEM_DEVICE
+    select VIRTIO_MD
 
 config VHOST_VSOCK_COMMON
     bool
diff --git a/hw/virtio/meson.build b/hw/virtio/meson.build
index c4f4fe0..13e7c6c 100644
--- a/hw/virtio/meson.build
+++ b/hw/virtio/meson.build
@@ -63,6 +63,7 @@ virtio_pci_ss.add(when: 'CONFIG_VIRTIO_PMEM', if_true: files('virtio-pmem-pci.c'
 virtio_pci_ss.add(when: 'CONFIG_VIRTIO_IOMMU', if_true: files('virtio-iommu-pci.c'))
 virtio_pci_ss.add(when: 'CONFIG_VIRTIO_MEM', if_true: files('virtio-mem-pci.c'))
 virtio_pci_ss.add(when: 'CONFIG_VHOST_VDPA_DEV', if_true: files('vdpa-dev-pci.c'))
+virtio_pci_ss.add(when: 'CONFIG_VIRTIO_MD', if_true: files('virtio-md-pci.c'))
 
 specific_virtio_ss.add_all(when: 'CONFIG_VIRTIO_PCI', if_true: virtio_pci_ss)
 
diff --git a/hw/virtio/virtio-md-pci.c b/hw/virtio/virtio-md-pci.c
new file mode 100644
index 0000000..62bfb79
--- /dev/null
+++ b/hw/virtio/virtio-md-pci.c
@@ -0,0 +1,151 @@
+/*
+ * Abstract virtio based memory device
+ *
+ * Copyright (C) 2023 Red Hat, Inc.
+ *
+ * Authors:
+ *  David Hildenbrand <david@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "hw/virtio/virtio-md-pci.h"
+#include "hw/mem/memory-device.h"
+#include "qapi/error.h"
+#include "qemu/error-report.h"
+
+void virtio_md_pci_pre_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
+{
+    DeviceState *dev = DEVICE(vmd);
+    HotplugHandler *bus_handler = qdev_get_bus_hotplug_handler(dev);
+    MemoryDeviceState *md = MEMORY_DEVICE(vmd);
+    Error *local_err = NULL;
+
+    if (!bus_handler && dev->hotplugged) {
+        /*
+         * Without a bus hotplug handler, we cannot control the plug/unplug
+         * order. We should never reach this point when hotplugging on x86,
+         * however, better add a safety net.
+         */
+        error_setg(errp, "hotplug of virtio based memory devices not supported"
+                   " on this bus.");
+        return;
+    }
+    /*
+     * First, see if we can plug this memory device at all. If that
+     * succeeds, branch of to the actual hotplug handler.
+     */
+    memory_device_pre_plug(md, ms, NULL, &local_err);
+    if (!local_err && bus_handler) {
+        hotplug_handler_pre_plug(bus_handler, dev, &local_err);
+    }
+    error_propagate(errp, local_err);
+}
+
+void virtio_md_pci_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
+{
+    DeviceState *dev = DEVICE(vmd);
+    HotplugHandler *bus_handler = qdev_get_bus_hotplug_handler(dev);
+    MemoryDeviceState *md = MEMORY_DEVICE(vmd);
+    Error *local_err = NULL;
+
+    /*
+     * Plug the memory device first and then branch off to the actual
+     * hotplug handler. If that one fails, we can easily undo the memory
+     * device bits.
+     */
+    memory_device_plug(md, ms);
+    if (bus_handler) {
+        hotplug_handler_plug(bus_handler, dev, &local_err);
+        if (local_err) {
+            memory_device_unplug(md, ms);
+        }
+    }
+    error_propagate(errp, local_err);
+}
+
+void virtio_md_pci_unplug_request(VirtIOMDPCI *vmd, MachineState *ms,
+                                  Error **errp)
+{
+    VirtIOMDPCIClass *vmdc = VIRTIO_MD_PCI_GET_CLASS(vmd);
+    DeviceState *dev = DEVICE(vmd);
+    HotplugHandler *bus_handler = qdev_get_bus_hotplug_handler(dev);
+    HotplugHandlerClass *hdc;
+    Error *local_err = NULL;
+
+    if (!vmdc->unplug_request_check) {
+        error_setg(errp, "this virtio based memory devices cannot be unplugged");
+        return;
+    }
+
+    if (!bus_handler) {
+        error_setg(errp, "hotunplug of virtio based memory devices not"
+                   "supported on this bus");
+        return;
+    }
+
+    vmdc->unplug_request_check(vmd, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    /*
+     * Forward the async request or turn it into a sync request (handling it
+     * like qdev_unplug()).
+     */
+    hdc = HOTPLUG_HANDLER_GET_CLASS(bus_handler);
+    if (hdc->unplug_request) {
+        hotplug_handler_unplug_request(bus_handler, dev, &local_err);
+    } else {
+        virtio_md_pci_unplug(vmd, ms, &local_err);
+        if (!local_err) {
+            object_unparent(OBJECT(dev));
+        }
+    }
+}
+
+void virtio_md_pci_unplug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
+{
+    DeviceState *dev = DEVICE(vmd);
+    HotplugHandler *bus_handler = qdev_get_bus_hotplug_handler(dev);
+    MemoryDeviceState *md = MEMORY_DEVICE(vmd);
+    Error *local_err = NULL;
+
+    /* Unplug the memory device while it is still realized. */
+    memory_device_unplug(md, ms);
+
+    if (bus_handler) {
+        hotplug_handler_unplug(bus_handler, dev, &local_err);
+        if (local_err) {
+            /* Not expected to fail ... but still try to recover. */
+            memory_device_plug(md, ms);
+            error_propagate(errp, local_err);
+            return;
+        }
+    } else {
+        /* Very unexpected, but let's just try to do the right thing. */
+        warn_report("Unexpected unplug of virtio based memory device");
+        qdev_unrealize(dev);
+    }
+}
+
+static const TypeInfo virtio_md_pci_info = {
+    .name = TYPE_VIRTIO_MD_PCI,
+    .parent = TYPE_VIRTIO_PCI,
+    .instance_size = sizeof(VirtIOMDPCI),
+    .class_size = sizeof(VirtIOMDPCIClass),
+    .abstract = true,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_MEMORY_DEVICE },
+        { }
+    },
+};
+
+static void virtio_md_pci_register(void)
+{
+    type_register_static(&virtio_md_pci_info);
+}
+type_init(virtio_md_pci_register)
diff --git a/hw/virtio/virtio-mem-pci.c b/hw/virtio/virtio-mem-pci.c
index b85c126..c4597e0 100644
--- a/hw/virtio/virtio-mem-pci.c
+++ b/hw/virtio/virtio-mem-pci.c
@@ -93,12 +93,53 @@ static void virtio_mem_pci_size_change_notify(Notifier *notifier, void *data)
     g_free(qom_path);
 }
 
+static void virtio_mem_pci_unplug_request_check(VirtIOMDPCI *vmd, Error **errp)
+{
+    VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(vmd);
+    VirtIOMEM *vmem = &pci_mem->vdev;
+    VirtIOMEMClass *vpc = VIRTIO_MEM_GET_CLASS(vmem);
+
+    vpc->unplug_request_check(vmem, errp);
+}
+
+static void virtio_mem_pci_get_requested_size(Object *obj, Visitor *v,
+                                              const char *name, void *opaque,
+                                              Error **errp)
+{
+    VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(obj);
+
+    object_property_get(OBJECT(&pci_mem->vdev), name, v, errp);
+}
+
+static void virtio_mem_pci_set_requested_size(Object *obj, Visitor *v,
+                                              const char *name, void *opaque,
+                                              Error **errp)
+{
+    VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(obj);
+    DeviceState *dev = DEVICE(obj);
+
+    /*
+     * If we passed virtio_mem_pci_unplug_request_check(), making sure that
+     * the requested size is 0, don't allow modifying the requested size
+     * anymore, otherwise the VM might end up hotplugging memory before
+     * handling the unplug request.
+     */
+    if (dev->pending_deleted_event) {
+        error_setg(errp, "'%s' cannot be changed if the device is in the"
+                   " process of unplug", name);
+        return;
+    }
+
+    object_property_set(OBJECT(&pci_mem->vdev), name, v, errp);
+}
+
 static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
     PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
     MemoryDeviceClass *mdc = MEMORY_DEVICE_CLASS(klass);
+    VirtIOMDPCIClass *vmdc = VIRTIO_MD_PCI_CLASS(klass);
 
     k->realize = virtio_mem_pci_realize;
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
@@ -111,6 +152,8 @@ static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
     mdc->get_memory_region = virtio_mem_pci_get_memory_region;
     mdc->fill_device_info = virtio_mem_pci_fill_device_info;
     mdc->get_min_alignment = virtio_mem_pci_get_min_alignment;
+
+    vmdc->unplug_request_check = virtio_mem_pci_unplug_request_check;
 }
 
 static void virtio_mem_pci_instance_init(Object *obj)
@@ -135,21 +178,18 @@ static void virtio_mem_pci_instance_init(Object *obj)
                               OBJECT(&dev->vdev), VIRTIO_MEM_BLOCK_SIZE_PROP);
     object_property_add_alias(obj, VIRTIO_MEM_SIZE_PROP, OBJECT(&dev->vdev),
                               VIRTIO_MEM_SIZE_PROP);
-    object_property_add_alias(obj, VIRTIO_MEM_REQUESTED_SIZE_PROP,
-                              OBJECT(&dev->vdev),
-                              VIRTIO_MEM_REQUESTED_SIZE_PROP);
+    object_property_add(obj, VIRTIO_MEM_REQUESTED_SIZE_PROP, "size",
+                        virtio_mem_pci_get_requested_size,
+                        virtio_mem_pci_set_requested_size, NULL, NULL);
 }
 
 static const VirtioPCIDeviceTypeInfo virtio_mem_pci_info = {
     .base_name = TYPE_VIRTIO_MEM_PCI,
+    .parent = TYPE_VIRTIO_MD_PCI,
     .generic_name = "virtio-mem-pci",
     .instance_size = sizeof(VirtIOMEMPCI),
     .instance_init = virtio_mem_pci_instance_init,
     .class_init = virtio_mem_pci_class_init,
-    .interfaces = (InterfaceInfo[]) {
-        { TYPE_MEMORY_DEVICE },
-        { }
-    },
 };
 
 static void virtio_mem_pci_register_types(void)
diff --git a/hw/virtio/virtio-mem-pci.h b/hw/virtio/virtio-mem-pci.h
index e636e1a..c50b51d 100644
--- a/hw/virtio/virtio-mem-pci.h
+++ b/hw/virtio/virtio-mem-pci.h
@@ -13,21 +13,21 @@
 #ifndef QEMU_VIRTIO_MEM_PCI_H
 #define QEMU_VIRTIO_MEM_PCI_H
 
-#include "hw/virtio/virtio-pci.h"
+#include "hw/virtio/virtio-md-pci.h"
 #include "hw/virtio/virtio-mem.h"
 #include "qom/object.h"
 
 typedef struct VirtIOMEMPCI VirtIOMEMPCI;
 
 /*
- * virtio-mem-pci: This extends VirtioPCIProxy.
+ * virtio-mem-pci: This extends VirtIOMDPCI.
  */
 #define TYPE_VIRTIO_MEM_PCI "virtio-mem-pci-base"
 DECLARE_INSTANCE_CHECKER(VirtIOMEMPCI, VIRTIO_MEM_PCI,
                          TYPE_VIRTIO_MEM_PCI)
 
 struct VirtIOMEMPCI {
-    VirtIOPCIProxy parent_obj;
+    VirtIOMDPCI parent_obj;
     VirtIOMEM vdev;
     Notifier size_change_notifier;
 };
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index ec0ae32..b6e7817 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -18,6 +18,7 @@
 #include "sysemu/numa.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/reset.h"
+#include "sysemu/runstate.h"
 #include "hw/virtio/virtio.h"
 #include "hw/virtio/virtio-bus.h"
 #include "hw/virtio/virtio-mem.h"
@@ -621,20 +622,20 @@ static int virtio_mem_unplug_all(VirtIOMEM *vmem)
 {
     RAMBlock *rb = vmem->memdev->mr.ram_block;
 
-    if (virtio_mem_is_busy()) {
-        return -EBUSY;
-    }
-
-    if (ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb))) {
-        return -EBUSY;
-    }
-    virtio_mem_notify_unplug_all(vmem);
-
-    bitmap_clear(vmem->bitmap, 0, vmem->bitmap_size);
     if (vmem->size) {
+        if (virtio_mem_is_busy()) {
+            return -EBUSY;
+        }
+        if (ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb))) {
+            return -EBUSY;
+        }
+        virtio_mem_notify_unplug_all(vmem);
+
+        bitmap_clear(vmem->bitmap, 0, vmem->bitmap_size);
         vmem->size = 0;
         notifier_list_notify(&vmem->size_change_notifiers, &vmem->size);
     }
+
     trace_virtio_mem_unplugged_all();
     virtio_mem_resize_usable_region(vmem, vmem->requested_size, true);
     return 0;
@@ -901,11 +902,23 @@ static void virtio_mem_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    ret = ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb));
-    if (ret) {
-        error_setg_errno(errp, -ret, "Unexpected error discarding RAM");
-        ram_block_coordinated_discard_require(false);
-        return;
+    /*
+     * We don't know at this point whether shared RAM is migrated using
+     * QEMU or migrated using the file content. "x-ignore-shared" will be
+     * configured after realizing the device. So in case we have an
+     * incoming migration, simply always skip the discard step.
+     *
+     * Otherwise, make sure that we start with a clean slate: either the
+     * memory backend might get reused or the shared file might still have
+     * memory allocated.
+     */
+    if (!runstate_check(RUN_STATE_INMIGRATE)) {
+        ret = ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb));
+        if (ret) {
+            error_setg_errno(errp, -ret, "Unexpected error discarding RAM");
+            ram_block_coordinated_discard_require(false);
+            return;
+        }
     }
 
     virtio_mem_resize_usable_region(vmem, vmem->requested_size, true);
@@ -977,10 +990,6 @@ static int virtio_mem_post_load(void *opaque, int version_id)
     RamDiscardListener *rdl;
     int ret;
 
-    if (vmem->prealloc && !vmem->early_migration) {
-        warn_report("Proper preallocation with migration requires a newer QEMU machine");
-    }
-
     /*
      * We started out with all memory discarded and our memory region is mapped
      * into an address space. Replay, now that we updated the bitmap.
@@ -993,6 +1002,18 @@ static int virtio_mem_post_load(void *opaque, int version_id)
         }
     }
 
+    /*
+     * If shared RAM is migrated using the file content and not using QEMU,
+     * don't mess with preallocation and postcopy.
+     */
+    if (migrate_ram_is_ignored(vmem->memdev->mr.ram_block)) {
+        return 0;
+    }
+
+    if (vmem->prealloc && !vmem->early_migration) {
+        warn_report("Proper preallocation with migration requires a newer QEMU machine");
+    }
+
     if (migration_in_incoming_postcopy()) {
         return 0;
     }
@@ -1026,6 +1047,14 @@ static int virtio_mem_post_load_early(void *opaque, int version_id)
     }
 
     /*
+     * If shared RAM is migrated using the file content and not using QEMU,
+     * don't mess with preallocation and postcopy.
+     */
+    if (migrate_ram_is_ignored(rb)) {
+        return 0;
+    }
+
+    /*
      * We restored the bitmap and verified that the basic properties
      * match on source and destination, so we can go ahead and preallocate
      * memory for all plugged memory blocks, before actual RAM migration starts
@@ -1483,6 +1512,30 @@ static void virtio_mem_rdm_unregister_listener(RamDiscardManager *rdm,
     QLIST_REMOVE(rdl, next);
 }
 
+static void virtio_mem_unplug_request_check(VirtIOMEM *vmem, Error **errp)
+{
+    if (vmem->unplugged_inaccessible == ON_OFF_AUTO_OFF) {
+        /*
+         * We could allow it with a usable region size of 0, but let's just
+         * not care about that legacy setting.
+         */
+        error_setg(errp, "virtio-mem device cannot get unplugged while"
+                   " '" VIRTIO_MEM_UNPLUGGED_INACCESSIBLE_PROP "' != 'on'");
+        return;
+    }
+
+    if (vmem->size) {
+        error_setg(errp, "virtio-mem device cannot get unplugged while"
+                   " '" VIRTIO_MEM_SIZE_PROP "' != '0'");
+        return;
+    }
+    if (vmem->requested_size) {
+        error_setg(errp, "virtio-mem device cannot get unplugged while"
+                   " '" VIRTIO_MEM_REQUESTED_SIZE_PROP "' != '0'");
+        return;
+    }
+}
+
 static void virtio_mem_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -1505,6 +1558,7 @@ static void virtio_mem_class_init(ObjectClass *klass, void *data)
     vmc->get_memory_region = virtio_mem_get_memory_region;
     vmc->add_size_change_notifier = virtio_mem_add_size_change_notifier;
     vmc->remove_size_change_notifier = virtio_mem_remove_size_change_notifier;
+    vmc->unplug_request_check = virtio_mem_unplug_request_check;
 
     rdmc->get_min_granularity = virtio_mem_rdm_get_min_granularity;
     rdmc->is_populated = virtio_mem_rdm_is_populated;
diff --git a/hw/virtio/virtio-pmem-pci.c b/hw/virtio/virtio-pmem-pci.c
index 197d219..cfe7f3b 100644
--- a/hw/virtio/virtio-pmem-pci.c
+++ b/hw/virtio/virtio-pmem-pci.c
@@ -110,13 +110,10 @@ static void virtio_pmem_pci_instance_init(Object *obj)
 static const VirtioPCIDeviceTypeInfo virtio_pmem_pci_info = {
     .base_name             = TYPE_VIRTIO_PMEM_PCI,
     .generic_name          = "virtio-pmem-pci",
+    .parent                = TYPE_VIRTIO_MD_PCI,
     .instance_size = sizeof(VirtIOPMEMPCI),
     .instance_init = virtio_pmem_pci_instance_init,
     .class_init    = virtio_pmem_pci_class_init,
-    .interfaces = (InterfaceInfo[]) {
-        { TYPE_MEMORY_DEVICE },
-        { }
-    },
 };
 
 static void virtio_pmem_pci_register_types(void)
diff --git a/hw/virtio/virtio-pmem-pci.h b/hw/virtio/virtio-pmem-pci.h
index 63cfe72..88b01ce 100644
--- a/hw/virtio/virtio-pmem-pci.h
+++ b/hw/virtio/virtio-pmem-pci.h
@@ -14,21 +14,21 @@
 #ifndef QEMU_VIRTIO_PMEM_PCI_H
 #define QEMU_VIRTIO_PMEM_PCI_H
 
-#include "hw/virtio/virtio-pci.h"
+#include "hw/virtio/virtio-md-pci.h"
 #include "hw/virtio/virtio-pmem.h"
 #include "qom/object.h"
 
 typedef struct VirtIOPMEMPCI VirtIOPMEMPCI;
 
 /*
- * virtio-pmem-pci: This extends VirtioPCIProxy.
+ * virtio-pmem-pci: This extends VirtIOMDPCI.
  */
 #define TYPE_VIRTIO_PMEM_PCI "virtio-pmem-pci-base"
 DECLARE_INSTANCE_CHECKER(VirtIOPMEMPCI, VIRTIO_PMEM_PCI,
                          TYPE_VIRTIO_PMEM_PCI)
 
 struct VirtIOPMEMPCI {
-    VirtIOPCIProxy parent_obj;
+    VirtIOMDPCI parent_obj;
     VirtIOPMEM vdev;
 };
 
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 12d9e9d..ed83360 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -37,6 +37,7 @@ void machine_parse_smp_config(MachineState *ms,
                               const SMPConfiguration *config, Error **errp);
 unsigned int machine_topo_get_cores_per_socket(const MachineState *ms);
 unsigned int machine_topo_get_threads_per_socket(const MachineState *ms);
+void machine_memory_devices_init(MachineState *ms, hwaddr base, uint64_t size);
 
 /**
  * machine_class_allow_dynamic_sysbus_dev: Add type to list of valid devices
@@ -297,11 +298,13 @@ struct MachineClass {
  * address space for memory devices starts
  * @mr: address space container for memory devices
  * @dimm_size: the sum of plugged DIMMs' sizes
+ * @used_region_size: the part of @mr already used by memory devices
  */
 typedef struct DeviceMemoryState {
     hwaddr base;
     MemoryRegion mr;
     uint64_t dimm_size;
+    uint64_t used_region_size;
 } DeviceMemoryState;
 
 /**
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index c34c698..d54e8b1 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -60,7 +60,6 @@ typedef struct PCMachineState {
 
 #define PC_MACHINE_ACPI_DEVICE_PROP "acpi-device"
 #define PC_MACHINE_MAX_RAM_BELOW_4G "max-ram-below-4g"
-#define PC_MACHINE_DEVMEM_REGION_SIZE "device-memory-region-size"
 #define PC_MACHINE_VMPORT           "vmport"
 #define PC_MACHINE_SMBUS            "smbus"
 #define PC_MACHINE_SATA             "sata"
diff --git a/include/hw/virtio/virtio-md-pci.h b/include/hw/virtio/virtio-md-pci.h
new file mode 100644
index 0000000..5912e16
--- /dev/null
+++ b/include/hw/virtio/virtio-md-pci.h
@@ -0,0 +1,44 @@
+/*
+ * Abstract virtio based memory device
+ *
+ * Copyright (C) 2023 Red Hat, Inc.
+ *
+ * Authors:
+ *  David Hildenbrand <david@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef HW_VIRTIO_MD_PCI_H
+#define HW_VIRTIO_MD_PCI_H
+
+#include "hw/virtio/virtio-pci.h"
+#include "qom/object.h"
+
+/*
+ * virtio-md-pci: This extends VirtioPCIProxy.
+ */
+#define TYPE_VIRTIO_MD_PCI "virtio-md-pci"
+
+OBJECT_DECLARE_TYPE(VirtIOMDPCI, VirtIOMDPCIClass, VIRTIO_MD_PCI)
+
+struct VirtIOMDPCIClass {
+    /* private */
+    VirtioPCIClass parent;
+
+    /* public */
+    void (*unplug_request_check)(VirtIOMDPCI *vmd, Error **errp);
+};
+
+struct VirtIOMDPCI {
+    VirtIOPCIProxy parent_obj;
+};
+
+void virtio_md_pci_pre_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp);
+void virtio_md_pci_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp);
+void virtio_md_pci_unplug_request(VirtIOMDPCI *vmd, MachineState *ms,
+                                  Error **errp);
+void virtio_md_pci_unplug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp);
+
+#endif
diff --git a/include/hw/virtio/virtio-mem.h b/include/hw/virtio/virtio-mem.h
index f15e561..ab0fe2b 100644
--- a/include/hw/virtio/virtio-mem.h
+++ b/include/hw/virtio/virtio-mem.h
@@ -98,6 +98,7 @@ struct VirtIOMEMClass {
     MemoryRegion *(*get_memory_region)(VirtIOMEM *vmem, Error **errp);
     void (*add_size_change_notifier)(VirtIOMEM *vmem, Notifier *notifier);
     void (*remove_size_change_notifier)(VirtIOMEM *vmem, Notifier *notifier);
+    void (*unplug_request_check)(VirtIOMEM *vmem, Error **errp);
 };
 
 #endif
diff --git a/include/migration/misc.h b/include/migration/misc.h
index 5ebe13b..7dcc0b5 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -40,6 +40,7 @@ int precopy_notify(PrecopyNotifyReason reason, Error **errp);
 
 void ram_mig_init(void);
 void qemu_guest_free_page_hint(void *addr, size_t len);
+bool migrate_ram_is_ignored(RAMBlock *block);
 
 /* migration/block.c */
 
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 5615ec2..29aea94 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -408,7 +408,7 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis, Error **errp)
     /*
      * We don't support postcopy with some type of ramblocks.
      *
-     * NOTE: we explicitly ignored ramblock_is_ignored() instead we checked
+     * NOTE: we explicitly ignored migrate_ram_is_ignored() instead we checked
      * all possible ramblocks.  This is because this function can be called
      * when creating the migration object, during the phase RAM_MIGRATABLE
      * is not even properly set for all the ramblocks.
diff --git a/migration/ram.c b/migration/ram.c
index 5283a75..0ada647 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -194,7 +194,7 @@ static bool postcopy_preempt_active(void)
     return migrate_postcopy_preempt() && migration_in_postcopy();
 }
 
-bool ramblock_is_ignored(RAMBlock *block)
+bool migrate_ram_is_ignored(RAMBlock *block)
 {
     return !qemu_ram_is_migratable(block) ||
            (migrate_ignore_shared() && qemu_ram_is_shared(block)
@@ -696,7 +696,7 @@ static void pss_find_next_dirty(PageSearchStatus *pss)
     unsigned long size = rb->used_length >> TARGET_PAGE_BITS;
     unsigned long *bitmap = rb->bmap;
 
-    if (ramblock_is_ignored(rb)) {
+    if (migrate_ram_is_ignored(rb)) {
         /* Points directly to the end, so we know no dirty page */
         pss->page = size;
         return;
@@ -780,7 +780,7 @@ unsigned long colo_bitmap_find_dirty(RAMState *rs, RAMBlock *rb,
 
     *num = 0;
 
-    if (ramblock_is_ignored(rb)) {
+    if (migrate_ram_is_ignored(rb)) {
         return size;
     }
 
@@ -2260,7 +2260,7 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
     unsigned long start_page = pss->page;
     int res;
 
-    if (ramblock_is_ignored(pss->block)) {
+    if (migrate_ram_is_ignored(pss->block)) {
         error_report("block %s should not be migrated !", pss->block->idstr);
         return 0;
     }
@@ -3347,7 +3347,7 @@ static inline RAMBlock *ram_block_from_stream(MigrationIncomingState *mis,
         return NULL;
     }
 
-    if (ramblock_is_ignored(block)) {
+    if (migrate_ram_is_ignored(block)) {
         error_report("block %s should not be migrated !", id);
         return NULL;
     }
@@ -3958,7 +3958,7 @@ static int ram_load_precopy(QEMUFile *f)
                     }
                     if (migrate_ignore_shared()) {
                         hwaddr addr = qemu_get_be64(f);
-                        if (ramblock_is_ignored(block) &&
+                        if (migrate_ram_is_ignored(block) &&
                             block->mr->addr != addr) {
                             error_report("Mismatched GPAs for block %s "
                                          "%" PRId64 "!= %" PRId64,
@@ -4254,7 +4254,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
     RAMBlock *rb = qemu_ram_block_from_host(host, false, &offset);
     Error *err = NULL;
 
-    if (ramblock_is_ignored(rb)) {
+    if (migrate_ram_is_ignored(rb)) {
         return;
     }
 
diff --git a/migration/ram.h b/migration/ram.h
index ea1f3c2..145c915 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -36,11 +36,10 @@
 extern XBZRLECacheStats xbzrle_counters;
 extern CompressionStats compression_counters;
 
-bool ramblock_is_ignored(RAMBlock *block);
 /* Should be holding either ram_list.mutex, or the RCU lock. */
 #define RAMBLOCK_FOREACH_NOT_IGNORED(block)            \
     INTERNAL_RAMBLOCK_FOREACH(block)                   \
-        if (ramblock_is_ignored(block)) {} else
+        if (migrate_ram_is_ignored(block)) {} else
 
 #define RAMBLOCK_FOREACH_MIGRATABLE(block)             \
     INTERNAL_RAMBLOCK_FOREACH(block)                   \
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index bda475a..3df7354 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3456,6 +3456,24 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
              * so a userfault will trigger.
              */
 #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+            /*
+             * We'll discard data from the actual file, even though we only
+             * have a MAP_PRIVATE mapping, possibly messing with other
+             * MAP_PRIVATE/MAP_SHARED mappings. There is no easy way to
+             * change that behavior whithout violating the promised
+             * semantics of ram_block_discard_range().
+             *
+             * Only warn, because it works as long as nobody else uses that
+             * file.
+             */
+            if (!qemu_ram_is_shared(rb)) {
+                warn_report_once("ram_block_discard_range: Discarding RAM"
+                                 " in private file mappings is possibly"
+                                 " dangerous, because it will modify the"
+                                 " underlying file and will affect other"
+                                 " users of the file");
+            }
+
             ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                             start, length);
             if (ret) {
diff --git a/stubs/meson.build b/stubs/meson.build
index a56645e..ef6e39a 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -60,6 +60,7 @@ if have_system
   stub_ss.add(files('semihost.c'))
   stub_ss.add(files('usb-dev-stub.c'))
   stub_ss.add(files('xen-hw-stub.c'))
+  stub_ss.add(files('virtio-md-pci.c'))
 else
   stub_ss.add(files('qdev.c'))
 endif
diff --git a/stubs/virtio-md-pci.c b/stubs/virtio-md-pci.c
new file mode 100644
index 0000000..ce5bba0
--- /dev/null
+++ b/stubs/virtio-md-pci.c
@@ -0,0 +1,24 @@
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "hw/virtio/virtio-md-pci.h"
+
+void virtio_md_pci_pre_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
+{
+    error_setg(errp, "virtio based memory devices not supported");
+}
+
+void virtio_md_pci_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
+{
+    error_setg(errp, "virtio based memory devices not supported");
+}
+
+void virtio_md_pci_unplug_request(VirtIOMDPCI *vmd, MachineState *ms,
+                                  Error **errp)
+{
+    error_setg(errp, "virtio based memory devices not supported");
+}
+
+void virtio_md_pci_unplug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
+{
+    error_setg(errp, "virtio based memory devices not supported");
+}