diff --git a/disas/riscv.c b/disas/riscv.c
index 793ad14c27..03c8dc9961 100644
--- a/disas/riscv.c
+++ b/disas/riscv.c
@@ -3090,3 +3090,8 @@ int print_insn_riscv64(bfd_vma memaddr, struct disassemble_info *info)
 {
     return print_insn_riscv(memaddr, info, rv64);
 }
+
+int print_insn_riscv128(bfd_vma memaddr, struct disassemble_info *info)
+{
+    return print_insn_riscv(memaddr, info, rv128);
+}
diff --git a/include/disas/dis-asm.h b/include/disas/dis-asm.h
index 08e1beec85..102a1e7f50 100644
--- a/include/disas/dis-asm.h
+++ b/include/disas/dis-asm.h
@@ -459,6 +459,7 @@ int print_insn_nios2(bfd_vma, disassemble_info*);
 int print_insn_xtensa           (bfd_vma, disassemble_info*);
 int print_insn_riscv32          (bfd_vma, disassemble_info*);
 int print_insn_riscv64          (bfd_vma, disassemble_info*);
+int print_insn_riscv128         (bfd_vma, disassemble_info*);
 int print_insn_rx(bfd_vma, disassemble_info *);
 int print_insn_hexagon(bfd_vma, disassemble_info *);
 
diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 1bd4a7c7aa..9bc25d3055 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -178,6 +178,19 @@ static void rv64_sifive_e_cpu_init(Object *obj)
     set_priv_version(env, PRIV_VERSION_1_10_0);
     qdev_prop_set_bit(DEVICE(obj), "mmu", false);
 }
+
+static void rv128_base_cpu_init(Object *obj)
+{
+    if (qemu_tcg_mttcg_enabled()) {
+        /* Missing 128-bit aligned atomics */
+        error_report("128-bit RISC-V currently does not work with Multi "
+                     "Threaded TCG. Please use: -accel tcg,thread=single");
+        exit(EXIT_FAILURE);
+    }
+    CPURISCVState *env = &RISCV_CPU(obj)->env;
+    /* We set this in the realise function */
+    set_misa(env, MXL_RV128, 0);
+}
 #else
 static void rv32_base_cpu_init(Object *obj)
 {
@@ -402,6 +415,9 @@ static void riscv_cpu_disas_set_info(CPUState *s, disassemble_info *info)
     case MXL_RV64:
         info->print_insn = print_insn_riscv64;
         break;
+    case MXL_RV128:
+        info->print_insn = print_insn_riscv128;
+        break;
     default:
         g_assert_not_reached();
     }
@@ -464,6 +480,8 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
 #ifdef TARGET_RISCV64
     case MXL_RV64:
         break;
+    case MXL_RV128:
+        break;
 #endif
     case MXL_RV32:
         break;
@@ -673,6 +691,7 @@ static gchar *riscv_gdb_arch_name(CPUState *cs)
     case MXL_RV32:
         return g_strdup("riscv:rv32");
     case MXL_RV64:
+    case MXL_RV128:
         return g_strdup("riscv:rv64");
     default:
         g_assert_not_reached();
@@ -827,6 +846,7 @@ static const TypeInfo riscv_cpu_type_infos[] = {
     DEFINE_CPU(TYPE_RISCV_CPU_SIFIVE_E51,       rv64_sifive_e_cpu_init),
     DEFINE_CPU(TYPE_RISCV_CPU_SIFIVE_U54,       rv64_sifive_u_cpu_init),
     DEFINE_CPU(TYPE_RISCV_CPU_SHAKTI_C,         rv64_sifive_u_cpu_init),
+    DEFINE_CPU(TYPE_RISCV_CPU_BASE128,          rv128_base_cpu_init),
 #endif
 };
 
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index fa5d238530..fd583e0f41 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -38,6 +38,7 @@
 #define TYPE_RISCV_CPU_ANY              RISCV_CPU_TYPE_NAME("any")
 #define TYPE_RISCV_CPU_BASE32           RISCV_CPU_TYPE_NAME("rv32")
 #define TYPE_RISCV_CPU_BASE64           RISCV_CPU_TYPE_NAME("rv64")
+#define TYPE_RISCV_CPU_BASE128          RISCV_CPU_TYPE_NAME("x-rv128")
 #define TYPE_RISCV_CPU_IBEX             RISCV_CPU_TYPE_NAME("lowrisc-ibex")
 #define TYPE_RISCV_CPU_SHAKTI_C         RISCV_CPU_TYPE_NAME("shakti-c")
 #define TYPE_RISCV_CPU_SIFIVE_E31       RISCV_CPU_TYPE_NAME("sifive-e31")
diff --git a/target/riscv/gdbstub.c b/target/riscv/gdbstub.c
index 881ab33392..a5429b92d4 100644
--- a/target/riscv/gdbstub.c
+++ b/target/riscv/gdbstub.c
@@ -280,6 +280,11 @@ static int riscv_gen_dynamic_csr_xml(CPUState *cs, int base_reg)
     int bitsize = 16 << env->misa_mxl_max;
     int i;
 
+    /* Until gdb knows about 128-bit registers */
+    if (bitsize > 64) {
+        bitsize = 64;
+    }
+
     g_string_printf(s, "<?xml version=\"1.0\"?>");
     g_string_append_printf(s, "<!DOCTYPE feature SYSTEM \"gdb-target.dtd\">");
     g_string_append_printf(s, "<feature name=\"org.gnu.gdb.riscv.csr\">");