KVM: selftests: Disable dirty logging with vCPUs running

Disabling dirty logging is much more intestesting from a testing
perspective if the vCPUs are still running. This also excercises the
code-path in which collapsible SPTEs must be faulted back in at a higher
level after disabling dirty logging.

To: linux-kselftest@vger.kernel.org
CC: Peter Xu <peterx@redhat.com>
CC: Andrew Jones <drjones@redhat.com>
CC: Thomas Huth <thuth@redhat.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210202185734.1680553-29-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/dirty_log_perf_test.c

@@ -211,18 +211,18 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 		}
 	}
 
-	/* Tell the vcpu thread to quit */
-	host_quit = true;
-	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++)
-		pthread_join(vcpu_threads[vcpu_id], NULL);
-
 	/* Disable dirty logging */
 	clock_gettime(CLOCK_MONOTONIC, &start);
 	vm_mem_region_set_flags(vm, PERF_TEST_MEM_SLOT_INDEX, 0);
 	ts_diff = timespec_elapsed(start);
 	pr_info("Disabling dirty logging time: %ld.%.9lds\n",
 		ts_diff.tv_sec, ts_diff.tv_nsec);
 
+	/* Tell the vcpu thread to quit */
+	host_quit = true;
+	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++)
+		pthread_join(vcpu_threads[vcpu_id], NULL);
+
 	avg = timespec_div(get_dirty_log_total, p->iterations);
 	pr_info("Get dirty log over %lu iterations took %ld.%.9lds. (Avg %ld.%.9lds/iteration)\n",
 		p->iterations, get_dirty_log_total.tv_sec,