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-rw-r--r--hw/i386/pc.c1
-rw-r--r--hw/i386/pc_piix.c1
-rw-r--r--hw/i386/pc_q35.c1
-rw-r--r--include/hw/boards.h1
-rw-r--r--numa.c21
-rw-r--r--vl.c3
6 files changed, 25 insertions, 3 deletions
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index fafe5ba5cd..c3afe5b7f1 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2347,6 +2347,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     mc->cpu_index_to_instance_props = pc_cpu_index_to_props;
     mc->get_default_cpu_node_id = pc_get_default_cpu_node_id;
     mc->possible_cpu_arch_ids = pc_possible_cpu_arch_ids;
+    mc->auto_enable_numa_with_memhp = true;
     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 f79d5cb694..5e47528993 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -446,6 +446,7 @@ 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->auto_enable_numa_with_memhp = false;
 }
 
 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 da3ea602e1..d6060043ac 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -318,6 +318,7 @@ 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->auto_enable_numa_with_memhp = false;
 }
 
 DEFINE_Q35_MACHINE(v2_10, "pc-q35-2.10", NULL,
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 62f160e0aa..156b16f7a6 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -197,6 +197,7 @@ struct MachineClass {
     bool ignore_memory_transaction_failures;
     int numa_mem_align_shift;
     const char **valid_cpu_types;
+    bool auto_enable_numa_with_memhp;
     void (*numa_auto_assign_ram)(MachineClass *mc, NodeInfo *nodes,
                                  int nb_nodes, ram_addr_t size);
 
diff --git a/numa.c b/numa.c
index 8d78d959f6..7151b24d1c 100644
--- a/numa.c
+++ b/numa.c
@@ -216,6 +216,7 @@ static void parse_numa_node(MachineState *ms, NumaNodeOptions *node,
     }
     numa_info[nodenr].present = true;
     max_numa_nodeid = MAX(max_numa_nodeid, nodenr + 1);
+    nb_numa_nodes++;
 }
 
 static void parse_numa_distance(NumaDistOptions *dist, Error **errp)
@@ -282,7 +283,6 @@ static int parse_numa(void *opaque, QemuOpts *opts, Error **errp)
         if (err) {
             goto end;
         }
-        nb_numa_nodes++;
         break;
     case NUMA_OPTIONS_TYPE_DIST:
         parse_numa_distance(&object->u.dist, &err);
@@ -433,6 +433,25 @@ void parse_numa_opts(MachineState *ms)
         exit(1);
     }
 
+    /*
+     * 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 automatically.
+     */
+    if (ms->ram_slots > 0 && nb_numa_nodes == 0 &&
+        mc->auto_enable_numa_with_memhp) {
+            NumaNodeOptions node = { };
+            parse_numa_node(ms, &node, NULL);
+    }
+
     assert(max_numa_nodeid <= MAX_NODES);
 
     /* No support for sparse NUMA node IDs yet: */
diff --git a/vl.c b/vl.c
index 7372424fa7..1ad1c04637 100644
--- a/vl.c
+++ b/vl.c
@@ -4690,8 +4690,6 @@ 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);
-
     if (qemu_opts_foreach(qemu_find_opts("mon"),
                           mon_init_func, NULL, NULL)) {
         exit(1);
@@ -4741,6 +4739,7 @@ int main(int argc, char **argv, char **envp)
     current_machine->boot_order = boot_order;
     current_machine->cpu_model = cpu_model;
 
+    parse_numa_opts(current_machine);
 
     /* parse features once if machine provides default cpu_type */
     if (machine_class->default_cpu_type) {