Use the recently added API to filter unavailable CPUs for a given
accelerator. At this moment this is the case for a QEMU built with KVM
and TCG support querying a binary running with TCG:

qemu-system-riscv64 -S -M virt,accel=tcg -display none
    -qmp tcp:localhost:1234,server,wait=off

./qemu/scripts/qmp/qmp-shell localhost:1234

(QEMU) query-cpu-model-expansion type=full model={"name":"host"}
{"error": {"class": "GenericError", "desc": "'host' CPU not available with tcg"}}

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/riscv-qmp-cmds.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/target/riscv/riscv-qmp-cmds.c b/target/riscv/riscv-qmp-cmds.c
index 5b2d186c83..2f2dbae7c8 100644
--- a/target/riscv/riscv-qmp-cmds.c
+++ b/target/riscv/riscv-qmp-cmds.c
@@ -31,6 +31,8 @@
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/visitor.h"
 #include "qom/qom-qobject.h"
+#include "sysemu/kvm.h"
+#include "sysemu/tcg.h"
 #include "cpu-qom.h"
 #include "cpu.h"
 
@@ -63,6 +65,17 @@ CpuDefinitionInfoList *qmp_query_cpu_definitions(Error **errp)
     return cpu_list;
 }
 
+static void riscv_check_if_cpu_available(RISCVCPU *cpu, Error **errp)
+{
+    if (!riscv_cpu_accelerator_compatible(cpu)) {
+        g_autofree char *name = riscv_cpu_get_name(cpu);
+        const char *accel = kvm_enabled() ? "kvm" : "tcg";
+
+        error_setg(errp, "'%s' CPU not available with %s", name, accel);
+        return;
+    }
+}
+
 static void riscv_obj_add_qdict_prop(Object *obj, QDict *qdict_out,
                                      const char *name)
 {
@@ -161,6 +174,13 @@ CpuModelExpansionInfo *qmp_query_cpu_model_expansion(CpuModelExpansionType type,
 
     obj = object_new(object_class_get_name(oc));
 
+    riscv_check_if_cpu_available(RISCV_CPU(obj), &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        object_unref(obj);
+        return NULL;
+    }
+
     if (qdict_in) {
         riscv_cpuobj_validate_qdict_in(obj, model->props, qdict_in,
                                        &local_err);
-- 
2.41.0