tests/qtest: Adjust and document query-cpu-model-expansion test for arm

We're about to move the 32-bit CPUs under CONFIG_TCG, so adjust the
query-cpu-model-expansion test to check against the cortex-a7, which
is already under CONFIG_TCG. That allows the next patch to contain
only code movement. (All the test cares about is that the CPU type
it's checking is one which definitely doesn't work under KVM.)

While here add comments clarifying what we're testing.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-id: 20230426180013.14814-7-farosas@suse.de
Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/qtest/arm-cpu-features.c

@@ -506,9 +506,23 @@ static void test_query_cpu_model_expansion_kvm(const void *data)
         QDict *resp;
         char *error;
 
-        assert_error(qts, "cortex-a15",
-            "We cannot guarantee the CPU type 'cortex-a15' works "
-            "with KVM on this host", NULL);
+        /*
+         * When using KVM, only the 'host' and 'max' CPU models are
+         * supported. Test that we're emitting a suitable error for
+         * unsupported CPU models.
+         */
+        if (qtest_has_accel("tcg")) {
+            assert_error(qts, "cortex-a7",
+                         "We cannot guarantee the CPU type 'cortex-a7' works "
+                         "with KVM on this host", NULL);
+        } else {
+            /*
+             * With a KVM-only build the 32-bit CPUs are not present.
+             */
+            assert_error(qts, "cortex-a7",
+                         "The CPU type 'cortex-a7' is not a "
+                         "recognized ARM CPU type", NULL);
+        }
 
         assert_has_feature_enabled(qts, "host", "aarch64");