Re: [PATCH v2 08/10] cpus: expose only realized vCPUs to global &cpus_queue

[Philippe Mathieu-Daudé]

On 7/2/25 17:20, Igor Mammedov wrote:

cpu_list_add() was doing 2 distinct things:
- assign some index to vCPU
- add unrealized (thus in inconsistent state) vCPU to &cpus_queue

Code using CPU_FOREACH() macro would iterate over possibly
unrealized vCPUs, often dealt with special casing.

Instead of working around of vCPU existence in cpus_queue,
split out cpu_index assignment from cpu_list_add(),

Better split 2 distinct changes in 2 patches for clarity.

and move the later to the end of realize stage,
right before vCPU is let run.

Signed-off-by: Igor Mammedov <imamm...@redhat.com>
---
CC: Yanan Wang <wangyana...@huawei.com>
CC: Zhao Liu <zhao1....@intel.com>
---
  include/hw/core/cpu.h |  6 ++++++
  cpu-common.c          | 23 ++++++++++++++---------
  cpu-target.c          |  2 +-
  hw/core/cpu-common.c  |  2 ++
  4 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index fb397cdfc5..c338fd31bd 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -750,6 +750,12 @@ bool cpu_virtio_is_big_endian(CPUState *cpu);

#endif /* CONFIG_USER_ONLY */ +/**

+ * cpu_auto_assign_cpu_index:
+ * @cpu: The CPU to be assigned a cpu_index
+ */
+void cpu_auto_assign_cpu_index(CPUState *cpu);
+
  /**
   * cpu_list_add:
   * @cpu: The CPU to be added to the list of CPUs.
diff --git a/cpu-common.c b/cpu-common.c
index 4248b2d727..92f3d00e56 100644
--- a/cpu-common.c
+++ b/cpu-common.c
@@ -71,15 +71,7 @@ int cpu_get_free_index(void)
      return max_cpu_index;
  }

-CPUTailQ cpus_queue = QTAILQ_HEAD_INITIALIZER(cpus_queue);

-static unsigned int cpu_list_generation_id;
-
-unsigned int cpu_list_generation_id_get(void)
-{
-    return cpu_list_generation_id;
-}
-
-void cpu_list_add(CPUState *cpu)
+void cpu_auto_assign_cpu_index(CPUState *cpu)
  {
      static bool cpu_index_auto_assigned;

@@ -91,6 +83,19 @@ void cpu_list_add(CPUState *cpu)

      } else {
          assert(!cpu_index_auto_assigned);
      }
+}
+
+CPUTailQ cpus_queue = QTAILQ_HEAD_INITIALIZER(cpus_queue);
+static unsigned int cpu_list_generation_id;
+
+unsigned int cpu_list_generation_id_get(void)
+{
+    return cpu_list_generation_id;
+}
+
+void cpu_list_add(CPUState *cpu)
+{
+    QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
      QTAILQ_INSERT_TAIL_RCU(&cpus_queue, cpu, node);
      cpu_list_generation_id++;
  }
diff --git a/cpu-target.c b/cpu-target.c
index 667688332c..0c86c18a50 100644
--- a/cpu-target.c
+++ b/cpu-target.c
@@ -142,7 +142,7 @@ bool cpu_exec_realizefn(CPUState *cpu, Error **errp)
      }

/* Wait until cpu initialization complete before exposing cpu. */

-    cpu_list_add(cpu);
+    cpu_auto_assign_cpu_index(cpu);

#ifdef CONFIG_USER_ONLY

      assert(qdev_get_vmsd(DEVICE(cpu)) == NULL ||
diff --git a/hw/core/cpu-common.c b/hw/core/cpu-common.c
index cb79566cc5..c29737e5e3 100644
--- a/hw/core/cpu-common.c
+++ b/hw/core/cpu-common.c
@@ -211,6 +211,8 @@ static void cpu_common_realizefn(DeviceState *dev, Error 
**errp)
          }
      }

+ cpu_list_add(cpu);

+
      if (dev->hotplugged) {
          cpu_synchronize_post_init(cpu);
          cpu_resume(cpu);