accel/tcg: Complete cpu initialization before registration

Delay cpu_list_add until realize is complete, so that cross-cpu
interaction does not happen with incomplete cpu state.  For this,
we must delay plugin initialization out of tcg_exec_realizefn,
because no cpu_index has been assigned.

Fixes a problem with cross-cpu jump cache flushing, when the
jump cache has not yet been allocated.

Fixes: a976a99a2975 ("include/hw/core: Create struct CPUJumpCache")
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reported-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/cpu-exec.c

@@ -1052,23 +1052,25 @@ void tcg_exec_realizefn(CPUState *cpu, Error **errp)
         cc->tcg_ops->initialize();
         tcg_target_initialized = true;
     }
-    tlb_init(cpu);
-    qemu_plugin_vcpu_init_hook(cpu);
 
+    cpu->tb_jmp_cache = g_new0(CPUJumpCache, 1);
+    tlb_init(cpu);
 #ifndef CONFIG_USER_ONLY
     tcg_iommu_init_notifier_list(cpu);
 #endif /* !CONFIG_USER_ONLY */
+    /* qemu_plugin_vcpu_init_hook delayed until cpu_index assigned. */
 }
 
 /* undo the initializations in reverse order */
 void tcg_exec_unrealizefn(CPUState *cpu)
 {
+    qemu_plugin_vcpu_exit_hook(cpu);
 #ifndef CONFIG_USER_ONLY
     tcg_iommu_free_notifier_list(cpu);
 #endif /* !CONFIG_USER_ONLY */
 
-    qemu_plugin_vcpu_exit_hook(cpu);
     tlb_destroy(cpu);
+    g_free(cpu->tb_jmp_cache);
 }
 
 #ifndef CONFIG_USER_ONLY

accel/tcg/translate-all.c

@@ -1580,15 +1580,13 @@ void tcg_flush_jmp_cache(CPUState *cpu)
 {
     CPUJumpCache *jc = cpu->tb_jmp_cache;
 
-    if (likely(jc)) {
-        for (int i = 0; i < TB_JMP_CACHE_SIZE; i++) {
-            qatomic_set(&jc->array[i].tb, NULL);
-        }
-    } else {
-        /* This should happen once during realize, and thus never race. */
-        jc = g_new0(CPUJumpCache, 1);
-        jc = qatomic_xchg(&cpu->tb_jmp_cache, jc);
-        assert(jc == NULL);
+    /* During early initialization, the cache may not yet be allocated. */
+    if (unlikely(jc == NULL)) {
+        return;
+    }
+
+    for (int i = 0; i < TB_JMP_CACHE_SIZE; i++) {
+        qatomic_set(&jc->array[i].tb, NULL);
     }
 }
 

cpu.c

@@ -134,15 +134,23 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
     /* cache the cpu class for the hotpath */
     cpu->cc = CPU_GET_CLASS(cpu);
 
-    cpu_list_add(cpu);
     if (!accel_cpu_realizefn(cpu, errp)) {
         return;
     }
+
     /* NB: errp parameter is unused currently */
     if (tcg_enabled()) {
         tcg_exec_realizefn(cpu, errp);
     }
 
+    /* Wait until cpu initialization complete before exposing cpu. */
+    cpu_list_add(cpu);
+
+    /* Plugin initialization must wait until cpu_index assigned. */
+    if (tcg_enabled()) {
+        qemu_plugin_vcpu_init_hook(cpu);
+    }
+
 #ifdef CONFIG_USER_ONLY
     assert(qdev_get_vmsd(DEVICE(cpu)) == NULL ||
            qdev_get_vmsd(DEVICE(cpu))->unmigratable);