diff --git a/hw/pc.h b/hw/pc.h
index e4db071..d6cc43b 100644
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -10,6 +10,7 @@
 #include "memory.h"
 #include "ioapic.h"
 
+#define PCI_HOLE_START 0xe0000000
 /* PC-style peripherals (also used by other machines).  */
 
 /* serial.c */
diff --git a/hw/pc_piix.c b/hw/pc_piix.c
index 88ff041..17db95a 100644
--- a/hw/pc_piix.c
+++ b/hw/pc_piix.c
@@ -43,6 +43,7 @@
 #include "xen.h"
 #include "memory.h"
 #include "exec-memory.h"
+#include "dimm.h"
 #ifdef CONFIG_XEN
 #  include <xen/hvm/hvm_info_table.h>
 #endif
@@ -52,6 +53,8 @@
 static const int ide_iobase[MAX_IDE_BUS] = { 0x1f0, 0x170 };
 static const int ide_iobase2[MAX_IDE_BUS] = { 0x3f6, 0x376 };
 static const int ide_irq[MAX_IDE_BUS] = { 14, 15 };
+static ram_addr_t below_4g_hp_mem_size = 0;
+static ram_addr_t above_4g_hp_mem_size = 0;
 
 static void kvm_piix3_setup_irq_routing(bool pci_enabled)
 {
@@ -117,6 +120,41 @@ static void ioapic_init(GSIState *gsi_state)
     }
 }
 
+static target_phys_addr_t pc_set_hp_memory_offset(uint64_t size)
+{
+    target_phys_addr_t ret;
+    static ram_addr_t ram_hp_offset = 0;
+
+    /* on first call, initialize ram_hp_offset */
+    if (!ram_hp_offset) {
+        if (ram_size >= PCI_HOLE_START ) {
+            ram_hp_offset = 0x100000000LL + (ram_size - PCI_HOLE_START);
+        } else {
+            ram_hp_offset = ram_size;
+        }
+    }
+
+    if (ram_hp_offset >= 0x100000000LL) {
+        ret = ram_hp_offset;
+        above_4g_hp_mem_size += size;
+        ram_hp_offset += size;
+    }
+    /* if dimm fits before pci hole, append it normally */
+    else if (ram_hp_offset + size <= PCI_HOLE_START) {
+        ret = ram_hp_offset;
+        below_4g_hp_mem_size += size;
+        ram_hp_offset += size;
+    }
+    /* otherwise place it above 4GB */
+    else {
+        ret = 0x100000000LL;
+        above_4g_hp_mem_size += size;
+        ram_hp_offset = 0x100000000LL + size;
+    }
+
+    return ret;
+}
+
 /* PC hardware initialisation */
 static void pc_init1(MemoryRegion *system_memory,
                      MemoryRegion *system_io,
@@ -155,9 +193,9 @@ static void pc_init1(MemoryRegion *system_memory,
         kvmclock_create();
     }
 
-    if (ram_size >= 0xe0000000 ) {
-        above_4g_mem_size = ram_size - 0xe0000000;
-        below_4g_mem_size = 0xe0000000;
+    if (ram_size >= PCI_HOLE_START ) {
+        above_4g_mem_size = ram_size - PCI_HOLE_START;
+        below_4g_mem_size = PCI_HOLE_START;
     } else {
         above_4g_mem_size = 0;
         below_4g_mem_size = ram_size;
@@ -172,6 +210,9 @@ static void pc_init1(MemoryRegion *system_memory,
         rom_memory = system_memory;
     }
 
+    /* adjust memory map for hotplug dimms */
+    dimm_calc_offsets(pc_set_hp_memory_offset);
+
     /* allocate ram and load rom/bios */
     if (!xen_enabled()) {
         fw_cfg = pc_memory_init(system_memory,
@@ -192,18 +233,22 @@ static void pc_init1(MemoryRegion *system_memory,
     if (pci_enabled) {
         pci_bus = i440fx_init(&i440fx_state, &piix3_devfn, &isa_bus, gsi,
                               system_memory, system_io, ram_size,
-                              below_4g_mem_size,
-                              0x100000000ULL - below_4g_mem_size,
-                              0x100000000ULL + above_4g_mem_size,
+                              below_4g_mem_size + below_4g_hp_mem_size,
+                              0x100000000ULL - below_4g_mem_size
+                                - below_4g_hp_mem_size,
+                              0x100000000ULL + above_4g_mem_size
+                                + above_4g_hp_mem_size,
                               (sizeof(target_phys_addr_t) == 4
                                ? 0
                                : ((uint64_t)1 << 62)),
                               pci_memory, ram_memory);
+        main_memory_bus_create(object_resolve_path("i440fx", NULL));
     } else {
         pci_bus = NULL;
         i440fx_state = NULL;
         isa_bus = isa_bus_new(NULL, system_io);
         no_hpet = 1;
+        main_memory_bus_create(object_resolve_path("isabus-bridge", NULL));
     }
     isa_bus_irqs(isa_bus, gsi);