[RFC PATCH 1/1] ACPI: Enforce mutual exclusion betwen CPU insertion and removal events

[Eric Mackay]

Setting a new pending event will clear a previously pending event
of the opposite type, for a given vCPU.

Intuitively, a physical CPU cannot be in the process of both
hotplugging and hot-unplugging at the same time.

Signed-off-by: Eric Mackay <eric.mackay@oracle.com>
---
 hw/acpi/cpu.c         | 36 ++++++++++++++++++++++++++++++++----
 include/hw/acpi/cpu.h |  4 ++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
index 5cb60ca8bc..48cb60dc38 100644
--- a/hw/acpi/cpu.c
+++ b/hw/acpi/cpu.c
@@ -23,6 +23,33 @@ enum {
     CPHP_CMD_MAX
 };
 
+// Enforce mutual exclusion between is_inserting and is_removing
+void acpi_cpu_set_inserting(AcpiCpuStatus *cdev, bool new_val)
+{
+    if (!cdev) {
+        return;
+    }
+
+    if (new_val) {
+        cdev->is_removing = false;
+    }
+
+    cdev->is_inserting = new_val;
+}
+
+void acpi_cpu_set_removing(AcpiCpuStatus *cdev, bool new_val)
+{
+    if (!cdev) {
+        return;
+    }
+
+    if (new_val) {
+        cdev->is_inserting = false;
+    }
+
+    cdev->is_removing = new_val;
+}
+
 static ACPIOSTInfo *acpi_cpu_device_status(int idx, AcpiCpuStatus *cdev)
 {
     ACPIOSTInfo *info = g_new0(ACPIOSTInfo, 1);
@@ -125,10 +152,10 @@ static void cpu_hotplug_wr(void *opaque, hwaddr addr, 
uint64_t data,
     case ACPI_CPU_FLAGS_OFFSET_RW: /* set is_* fields  */
         cdev = &cpu_st->devs[cpu_st->selector];
         if (data & 2) { /* clear insert event */
-            cdev->is_inserting = false;
+            acpi_cpu_set_inserting(cdev, false);
             trace_cpuhp_acpi_clear_inserting_evt(cpu_st->selector);
         } else if (data & 4) { /* clear remove event */
-            cdev->is_removing = false;
+            acpi_cpu_set_removing(cdev, false);
             trace_cpuhp_acpi_clear_remove_evt(cpu_st->selector);
         } else if (data & 8) {
             DeviceState *dev = NULL;
@@ -259,7 +286,7 @@ void acpi_cpu_plug_cb(HotplugHandler *hotplug_dev,
 
     cdev->cpu = CPU(dev);
     if (dev->hotplugged) {
-        cdev->is_inserting = true;
+        acpi_cpu_set_inserting(cdev, true);
         acpi_send_event(DEVICE(hotplug_dev), ACPI_CPU_HOTPLUG_STATUS);
     }
 }
@@ -272,10 +299,11 @@ void acpi_cpu_unplug_request_cb(HotplugHandler 
*hotplug_dev,
 
     cdev = get_cpu_status(cpu_st, dev);
     if (!cdev) {
+        warn_report("CPU status bad in unplug req cb\n");
         return;
     }
 
-    cdev->is_removing = true;
+    acpi_cpu_set_removing(cdev, true);
     acpi_send_event(DEVICE(hotplug_dev), ACPI_CPU_HOTPLUG_STATUS);
 }
 
diff --git a/include/hw/acpi/cpu.h b/include/hw/acpi/cpu.h
index 32654dc274..fde4ba4a37 100644
--- a/include/hw/acpi/cpu.h
+++ b/include/hw/acpi/cpu.h
@@ -39,6 +39,10 @@ typedef struct CPUHotplugState {
     AcpiCpuStatus *devs;
 } CPUHotplugState;
 
+// Enforce mutual exclusion between is_inserting and is_removing
+void acpi_cpu_set_inserting(AcpiCpuStatus *cdev, bool new_val);
+void acpi_cpu_set_removing(AcpiCpuStatus *cdev, bool new_val);
+
 void acpi_cpu_plug_cb(HotplugHandler *hotplug_dev,
                       CPUHotplugState *cpu_st, DeviceState *dev, Error **errp);
 
-- 
2.43.5