[Qemu-devel] [PATCH v5 2/3] pc & q35: Add new machine opt max-ram-below-4g

[Don Slutz]

This is a pc & q35 only machine opt.  One use is to allow for more
ram in a 32bit guest for example:

-machine pc,max-ram-below-4g=3.75G

If you add enough PCI devices then all mmio for them will not fit
below 4G which may not be the layout the user wanted. This allows
you to increase the below 4G address space that PCI devices can use
(aka decrease ram below 4G) and therefore in more cases not have any
mmio that is above 4G.

For example using "-machine pc,max-ram-below-4g=2G" on the command
line will limit the amount of ram that is below 4G to 2G.

Signed-off-by: Don Slutz <address@hidden>
---
v5:
  Re-work based on:

  https://github.com/imammedo/qemu/commits/memory-hotplug-v11


 hw/i386/pc.c         | 38 ++++++++++++++++++++++++++++++++++++++
 hw/i386/pc_piix.c    | 15 ++++++++++++---
 hw/i386/pc_q35.c     | 15 ++++++++++++---
 include/hw/i386/pc.h |  3 +++
 vl.c                 |  4 ++++
 5 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 7cdba10..bccb746 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1644,11 +1644,49 @@ pc_machine_get_hotplug_memory_region_size(Object *obj, 
Visitor *v, void *opaque,
     visit_type_int(v, &value, name, errp);
 }
 
+static void pc_machine_get_max_ram_below_4g(Object *obj, Visitor *v,
+                                         void *opaque, const char *name,
+                                         Error **errp)
+{
+    PCMachineState *pcms = PC_MACHINE(obj);
+    uint64_t value = pcms->max_ram_below_4g;
+
+    visit_type_size(v, &value, name, errp);
+}
+
+static void pc_machine_set_max_ram_below_4g(Object *obj, Visitor *v,
+                                         void *opaque, const char *name,
+                                         Error **errp)
+{
+    PCMachineState *pcms = PC_MACHINE(obj);
+    Error *error = NULL;
+    uint64_t value;
+
+    visit_type_size(v, &value, name, &error);
+    if (error) {
+        error_propagate(errp, error);
+        return;
+    }
+    if (value > (1ULL << 32)) {
+        error_set(&error, ERROR_CLASS_GENERIC_ERROR,
+                  "Machine option 'max-ram-below-4g=%"PRIu64
+                  "' expects size less then or equal to 4G", value);
+        error_propagate(errp, error);
+        return;
+    }
+
+    pcms->max_ram_below_4g = value;
+}
+
 static void pc_machine_initfn(Object *obj)
 {
     object_property_add(obj, PC_MACHINE_MEMHP_REGION_SIZE, "int",
                         pc_machine_get_hotplug_memory_region_size,
                         NULL, NULL, NULL, NULL);
+    object_property_add(obj, PC_MACHINE_MAX_RAM_BELOW_4G,  "size",
+                        pc_machine_get_max_ram_below_4g,
+                        pc_machine_set_max_ram_below_4g,
+                        NULL, NULL, NULL);
 }
 
 static void pc_machine_class_init(ObjectClass *oc, void *data)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 40f6eaf..25f4727 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -98,6 +98,13 @@ static void pc_init1(MachineState *machine,
     DeviceState *icc_bridge;
     FWCfgState *fw_cfg = NULL;
     PcGuestInfo *guest_info;
+    Object *mo = qdev_get_machine();
+    PCMachineState *pcms = PC_MACHINE(mo);
+    ram_addr_t lowmem = 0xe0000000;
+
+    if (pcms && pcms->max_ram_below_4g) {
+        lowmem = pcms->max_ram_below_4g;
+    }
 
     /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO memory).
      * If it doesn't, we need to split it in chunks below and above 4G.
@@ -106,8 +113,10 @@ static void pc_init1(MachineState *machine,
      * For old machine types, use whatever split we used historically to avoid
      * breaking migration.
      */
-    if (machine->ram_size >= 0xe0000000) {
-        ram_addr_t lowmem = gigabyte_align ? 0xc0000000 : 0xe0000000;
+    if (machine->ram_size >= lowmem) {
+        if (!(pcms && pcms->max_ram_below_4g) && gigabyte_align) {
+            lowmem = 0xc0000000;
+        }
         above_4g_mem_size = machine->ram_size - lowmem;
         below_4g_mem_size = lowmem;
     } else {
@@ -122,7 +131,7 @@ static void pc_init1(MachineState *machine,
     }
 
     icc_bridge = qdev_create(NULL, TYPE_ICC_BRIDGE);
-    object_property_add_child(qdev_get_machine(), "icc-bridge",
+    object_property_add_child(mo, "icc-bridge",
                               OBJECT(icc_bridge), NULL);
 
     pc_cpus_init(machine->cpu_model, icc_bridge);
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index e28ce40..155cdf1 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -85,6 +85,13 @@ static void pc_q35_init(MachineState *machine)
     PCIDevice *ahci;
     DeviceState *icc_bridge;
     PcGuestInfo *guest_info;
+    Object *mo = qdev_get_machine();
+    PCMachineState *pcms = PC_MACHINE(mo);
+    ram_addr_t lowmem = 0xb0000000;
+
+    if (pcms && pcms->max_ram_below_4g) {
+        lowmem = pcms->max_ram_below_4g;
+    }
 
     /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO memory
      * and 256 Mbytes for PCI Express Enhanced Configuration Access Mapping
@@ -95,8 +102,10 @@ static void pc_q35_init(MachineState *machine)
      * For old machine types, use whatever split we used historically to avoid
      * breaking migration.
      */
-    if (machine->ram_size >= 0xb0000000) {
-        ram_addr_t lowmem = gigabyte_align ? 0x80000000 : 0xb0000000;
+    if (machine->ram_size >= lowmem) {
+        if (!(pcms && pcms->max_ram_below_4g) && gigabyte_align) {
+            lowmem = 0x800000000;
+        }
         above_4g_mem_size = machine->ram_size - lowmem;
         below_4g_mem_size = lowmem;
     } else {
@@ -111,7 +120,7 @@ static void pc_q35_init(MachineState *machine)
     }
 
     icc_bridge = qdev_create(NULL, TYPE_ICC_BRIDGE);
-    object_property_add_child(qdev_get_machine(), "icc-bridge",
+    object_property_add_child(mo, "icc-bridge",
                               OBJECT(icc_bridge), NULL);
 
     pc_cpus_init(machine->cpu_model, icc_bridge);
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 19530bd..2d8b562 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -32,10 +32,13 @@ struct PCMachineState {
     MemoryRegion hotplug_memory;
 
     HotplugHandler *acpi_dev;
+
+    uint64_t max_ram_below_4g;
 };
 
 #define PC_MACHINE_ACPI_DEVICE_PROP "acpi-device"
 #define PC_MACHINE_MEMHP_REGION_SIZE "hotplug-memory-region-size"
+#define PC_MACHINE_MAX_RAM_BELOW_4G "max-ram-below-4g"
 
 /**
  * PCMachineClass:
diff --git a/vl.c b/vl.c
index 5e77a27..cffb9c5 100644
--- a/vl.c
+++ b/vl.c
@@ -382,6 +382,10 @@ static QemuOptsList qemu_machine_opts = {
             .name = "kvm-type",
             .type = QEMU_OPT_STRING,
             .help = "Specifies the KVM virtualization mode (HV, PR)",
+        },{
+            .name = PC_MACHINE_MAX_RAM_BELOW_4G,
+            .type = QEMU_OPT_SIZE,
+            .help = "maximum ram below the 4G boundary (32bit boundary)",
         },
         { /* End of list */ }
     },
-- 
1.8.4