[v2] NUMA: Enable adding NUMA node implicitly

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 2108104..7a753ee 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2349,6 +2349,7 @@  static void pc_machine_class_init(ObjectClass *oc, void *data)
     mc->get_hotplug_handler = pc_get_hotpug_handler;
     mc->cpu_index_to_instance_props = pc_cpu_index_to_props;
     mc->possible_cpu_arch_ids = pc_possible_cpu_arch_ids;
+    mc->add_numa_node_implicitly = numa_add_node_implicitly;
     mc->has_hotpluggable_cpus = true;
     mc->default_boot_order = "cad";
     mc->hot_add_cpu = pc_hot_add_cpu;
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index b03cc04..cc94334 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -452,6 +452,7 @@  static void pc_i440fx_2_10_machine_options(MachineClass *m)
     m->is_default = 0;
     m->alias = NULL;
     SET_MACHINE_COMPAT(m, PC_COMPAT_2_10);
+    m->add_numa_node_implicitly = NULL;
 }
 
 DEFINE_I440FX_MACHINE(v2_10, "pc-i440fx-2.10", NULL,
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index c1cba58..7329819 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -317,6 +317,7 @@  static void pc_q35_2_10_machine_options(MachineClass *m)
     m->alias = NULL;
     SET_MACHINE_COMPAT(m, PC_COMPAT_2_10);
     m->numa_auto_assign_ram = numa_legacy_auto_assign_ram;
+    m->add_numa_node_implicitly = NULL;
 }
 
 DEFINE_Q35_MACHINE(v2_10, "pc-q35-2.10", NULL,
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 7f044d1..c8c4f25 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -141,6 +141,8 @@  typedef struct {
  *    should instead use "unimplemented-device" for all memory ranges where
  *    the guest will attempt to probe for a device that QEMU doesn't
  *    implement and a stub device is required.
+ * @add_numa_node_implicitly:
+ *    Enable NUMA implicitly by add a new NUMA node automatically.
  */
 struct MachineClass {
     /*< private >*/
@@ -191,6 +193,8 @@  struct MachineClass {
     CpuInstanceProperties (*cpu_index_to_instance_props)(MachineState *machine,
                                                          unsigned cpu_index);
     const CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
+
+    void (*add_numa_node_implicitly)(QemuOptsList *list);
 };
 
 /**
diff --git a/include/sysemu/numa.h b/include/sysemu/numa.h
index 5c6df28..1660249 100644
--- a/include/sysemu/numa.h
+++ b/include/sysemu/numa.h
@@ -30,7 +30,7 @@  struct NumaNodeMem {
 };
 
 extern NodeInfo numa_info[MAX_NODES];
-void parse_numa_opts(MachineState *ms);
+void parse_numa_opts(MachineState *ms, uint64_t ram_slots);
 void query_numa_node_mem(NumaNodeMem node_mem[]);
 extern QemuOptsList qemu_numa_opts;
 void numa_set_mem_node_id(ram_addr_t addr, uint64_t size, uint32_t node);
@@ -41,4 +41,5 @@  void numa_legacy_auto_assign_ram(MachineClass *mc, NodeInfo *nodes,
 void numa_default_auto_assign_ram(MachineClass *mc, NodeInfo *nodes,
                                   int nb_nodes, ram_addr_t size);
 void numa_cpu_pre_plug(const CPUArchId *slot, DeviceState *dev, Error **errp);
+void numa_add_node_implicitly(QemuOptsList *list);
 #endif
diff --git a/numa.c b/numa.c
index fe066ad..470204d 100644
--- a/numa.c
+++ b/numa.c
@@ -423,12 +423,37 @@  void numa_default_auto_assign_ram(MachineClass *mc, NodeInfo *nodes,
     nodes[i].node_mem = size - usedmem;
 }
 
-void parse_numa_opts(MachineState *ms)
+void numa_add_node_implicitly(QemuOptsList *list)
+{
+    qemu_opts_parse_noisily(list, "node", true);
+}
+
+void parse_numa_opts(MachineState *ms, uint64_t ram_slots)
 {
     int i;
     MachineClass *mc = MACHINE_GET_CLASS(ms);
+    QemuOptsList *numa_opts = qemu_find_opts("numa");
+
+    /*
+     * If memory hotplug is enabled (slots > 0) but without '-numa'
+     * options explicitly on CLI, guestes will break.
+     *
+     *   Windows: won't enable memory hotplug without SRAT table at all
+     *
+     *   Linux: if QEMU is started with initial memory all below 4Gb
+     *   and no SRAT table present, guest kernel will use nommu DMA ops,
+     *   which breaks 32bit hw drivers when memory is hotplugged and
+     *   guest tries to use it with that drivers.
+     *
+     * Enable NUMA implicitly by adding a new NUMA node manually.
+     */
+    if (ram_slots > 0 && numa_opts->head.tqh_first == NULL) {
+        if (mc->add_numa_node_implicitly) {
+            mc->add_numa_node_implicitly(numa_opts);
+        }
+    }
 
-    if (qemu_opts_foreach(qemu_find_opts("numa"), parse_numa, ms, NULL)) {
+    if (qemu_opts_foreach(numa_opts, parse_numa, ms, NULL)) {
         exit(1);
     }
 
diff --git a/vl.c b/vl.c
index 9e62e92..1bd8eaf 100644
--- a/vl.c
+++ b/vl.c
@@ -4665,7 +4665,11 @@  int main(int argc, char **argv, char **envp)
     default_drive(default_floppy, snapshot, IF_FLOPPY, 0, FD_OPTS);
     default_drive(default_sdcard, snapshot, IF_SD, 0, SD_OPTS);
 
-    parse_numa_opts(current_machine);
+    current_machine->ram_size = ram_size;
+    current_machine->maxram_size = maxram_size;
+    current_machine->ram_slots = ram_slots;
+
+    parse_numa_opts(current_machine, ram_slots);
 
     if (qemu_opts_foreach(qemu_find_opts("mon"),
                           mon_init_func, NULL, NULL)) {
@@ -4710,9 +4714,6 @@  int main(int argc, char **argv, char **envp)
     replay_checkpoint(CHECKPOINT_INIT);
     qdev_machine_init();
 
-    current_machine->ram_size = ram_size;
-    current_machine->maxram_size = maxram_size;
-    current_machine->ram_slots = ram_slots;
     current_machine->boot_order = boot_order;
     current_machine->cpu_model = cpu_model;