diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 9596c7c7f1..2e788a0361 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -59,6 +59,7 @@
 #include "qapi/visitor.h"
 #include "standard-headers/linux/input.h"
 #include "hw/arm/smmuv3.h"
+#include "hw/acpi/acpi.h"
 
 #define DEFINE_VIRT_MACHINE_LATEST(major, minor, latest) \
     static void virt_##major##_##minor##_class_init(ObjectClass *oc, \
@@ -107,8 +108,8 @@
  * of a terabyte of RAM will be doing it on a host with more than a
  * terabyte of physical address space.)
  */
-#define RAMLIMIT_GB 255
-#define RAMLIMIT_BYTES (RAMLIMIT_GB * 1024ULL * 1024 * 1024)
+#define LEGACY_RAMLIMIT_GB 255
+#define LEGACY_RAMLIMIT_BYTES (LEGACY_RAMLIMIT_GB * GiB)
 
 /* Addresses and sizes of our components.
  * 0..128MB is space for a flash device so we can run bootrom code such as UEFI.
@@ -149,7 +150,8 @@ static const MemMapEntry base_memmap[] = {
     [VIRT_PCIE_MMIO] =          { 0x10000000, 0x2eff0000 },
     [VIRT_PCIE_PIO] =           { 0x3eff0000, 0x00010000 },
     [VIRT_PCIE_ECAM] =          { 0x3f000000, 0x01000000 },
-    [VIRT_MEM] =                { 0x40000000, RAMLIMIT_BYTES },
+    /* Actual RAM size depends on initial RAM and device memory settings */
+    [VIRT_MEM] =                { GiB, LEGACY_RAMLIMIT_BYTES },
 };
 
 /*
@@ -1370,7 +1372,8 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState *vms, int idx)
 
 static void virt_set_memmap(VirtMachineState *vms)
 {
-    hwaddr base;
+    MachineState *ms = MACHINE(vms);
+    hwaddr base, device_memory_base, device_memory_size;
     int i;
 
     vms->memmap = extended_memmap;
@@ -1379,7 +1382,32 @@ static void virt_set_memmap(VirtMachineState *vms)
         vms->memmap[i] = base_memmap[i];
     }
 
-    base = 256 * GiB; /* Top of the legacy initial RAM region */
+    if (ms->ram_slots > ACPI_MAX_RAM_SLOTS) {
+        error_report("unsupported number of memory slots: %"PRIu64,
+                     ms->ram_slots);
+        exit(EXIT_FAILURE);
+    }
+
+    /*
+     * We compute the base of the high IO region depending on the
+     * amount of initial and device memory. The device memory start/size
+     * is aligned on 1GiB. We never put the high IO region below 256GiB
+     * so that if maxram_size is < 255GiB we keep the legacy memory map.
+     * The device region size assumes 1GiB page max alignment per slot.
+     */
+    device_memory_base =
+        ROUND_UP(vms->memmap[VIRT_MEM].base + ms->ram_size, GiB);
+    device_memory_size = ms->maxram_size - ms->ram_size + ms->ram_slots * GiB;
+
+    /* Base address of the high IO region */
+    base = device_memory_base + ROUND_UP(device_memory_size, GiB);
+    if (base < device_memory_base) {
+        error_report("maxmem/slots too huge");
+        exit(EXIT_FAILURE);
+    }
+    if (base < vms->memmap[VIRT_MEM].base + LEGACY_RAMLIMIT_BYTES) {
+        base = vms->memmap[VIRT_MEM].base + LEGACY_RAMLIMIT_BYTES;
+    }
 
     for (i = VIRT_LOWMEMMAP_LAST; i < ARRAY_SIZE(extended_memmap); i++) {
         hwaddr size = extended_memmap[i].size;
@@ -1389,6 +1417,13 @@ static void virt_set_memmap(VirtMachineState *vms)
         vms->memmap[i].size = size;
         base += size;
     }
+    vms->highest_gpa = base - 1;
+    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);
+    }
 }
 
 static void machvirt_init(MachineState *machine)
@@ -1475,7 +1510,8 @@ static void machvirt_init(MachineState *machine)
     vms->smp_cpus = smp_cpus;
 
     if (machine->ram_size > vms->memmap[VIRT_MEM].size) {
-        error_report("mach-virt: cannot model more than %dGB RAM", RAMLIMIT_GB);
+        error_report("mach-virt: cannot model more than %dGB RAM",
+                     LEGACY_RAMLIMIT_GB);
         exit(1);
     }
 
@@ -1569,6 +1605,10 @@ static void machvirt_init(MachineState *machine)
     memory_region_allocate_system_memory(ram, NULL, "mach-virt.ram",
                                          machine->ram_size);
     memory_region_add_subregion(sysmem, vms->memmap[VIRT_MEM].base, ram);
+    if (machine->device_memory) {
+        memory_region_add_subregion(sysmem, machine->device_memory->base,
+                                    &machine->device_memory->mr);
+    }
 
     create_flash(vms, sysmem, secure_sysmem ? secure_sysmem : sysmem);
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index f3f7fae4ac..507517c603 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -131,6 +131,7 @@ typedef struct {
     uint32_t msi_phandle;
     uint32_t iommu_phandle;
     int psci_conduit;
+    hwaddr highest_gpa;
 } VirtMachineState;
 
 #define VIRT_ECAM_ID(high) (high ? VIRT_HIGH_PCIE_ECAM : VIRT_PCIE_ECAM)