pc & q35: Add new machine opt max-ram-below-4g

This is a pc & q35 only machine opt.

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.

Note: this machine option cannot be used to increase the amount
of ram below 4G.

Signed-off-by: Don Slutz <dslutz@verizon.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

MST: fix 32 bit

1 files changed, 47 insertions, 0 deletions

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 67eb450..2cf22b1 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1643,11 +1643,58 @@ 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 than or equal to 4G", value);
+        error_propagate(errp, error);
+        return;
+    }
+
+    if (value < (1ULL << 20)) {
+        error_report("Warning: small max_ram_below_4g(%"PRIu64
+                     ") less than 1M.  BIOS may not work..",
+                     value);
+    }
+
+    pcms->max_ram_below_4g = value;
+}
+
 static void pc_machine_initfn(Object *obj)
 {
+    PCMachineState *pcms = PC_MACHINE(obj);
+
     object_property_add(obj, PC_MACHINE_MEMHP_REGION_SIZE, "int",
                         pc_machine_get_hotplug_memory_region_size,
                         NULL, NULL, NULL, NULL);
+    pcms->max_ram_below_4g = 1ULL << 32; /* 4G */
+    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)