target/riscv/cpu.c: create KVM mock properties

KVM-specific properties are being created inside target/riscv/kvm.c. But
at this moment we're gathering all the remaining properties from TCG and
adding them as is when running KVM. This creates a situation where
non-KVM properties are setting flags to 'true' due to its default
settings (e.g.  Zawrs). Users can also freely enable them via command
line.

This doesn't impact runtime per se because KVM doesn't care about these
flags, but code such as riscv_isa_string_ext() take those flags into
account. The result is that, for a KVM guest, setting non-KVM properties
will make them appear in the riscv,isa DT.

We want to keep the same API for both TCG and KVM and at the same time,
when running KVM, forbid non-KVM extensions to be enabled internally. We
accomplish both by changing riscv_cpu_add_user_properties() to add a
mock boolean property for every non-KVM extension in
riscv_cpu_extensions[]. Then, when running KVM, users are still free to
set extensions at will, but we'll error out if a non-KVM extension is
enabled. Setting such extension to 'false' will be ignored.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230706101738.460804-18-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -1840,6 +1840,26 @@ static Property riscv_cpu_extensions[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+
+#ifndef CONFIG_USER_ONLY
+static void cpu_set_cfg_unavailable(Object *obj, Visitor *v,
+                                    const char *name,
+                                    void *opaque, Error **errp)
+{
+    const char *propname = opaque;
+    bool value;
+
+    if (!visit_type_bool(v, name, &value, errp)) {
+        return;
+    }
+
+    if (value) {
+        error_setg(errp, "extension %s is not available with KVM",
+                   propname);
+    }
+}
+#endif
+
 /*
  * Add CPU properties with user-facing flags.
  *
@@ -1868,6 +1888,22 @@ static void riscv_cpu_add_user_properties(Object *obj)
             if (object_property_find(obj, prop->name)) {
                 continue;
             }
+
+            /*
+             * Set the default to disabled for every extension
+             * unknown to KVM and error out if the user attempts
+             * to enable any of them.
+             *
+             * We're giving a pass for non-bool properties since they're
+             * not related to the availability of extensions and can be
+             * safely ignored as is.
+             */
+            if (prop->info == &qdev_prop_bool) {
+                object_property_add(obj, prop->name, "bool",
+                                    NULL, cpu_set_cfg_unavailable,
+                                    NULL, (void *)prop->name);
+                continue;
+            }
         }
 #endif
         qdev_property_add_static(dev, prop);