spapr: Ensure CPU cores are added contiguously and removed in LIFO order

If CPU core addition or removal is allowed in random order leading to
holes in the core id range (and hence in the cpu_index range), migration
can fail as migration with holes in cpu_index range isn't yet handled
correctly.

Prevent this situation by enforcing the addition in contiguous order
and removal in LIFO order so that we never end up with holes in
cpu_index range.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 20 insertions, 1 deletions

diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
index bc52b3c289..4bfc96bd5a 100644
--- a/hw/ppc/spapr_cpu_core.c
+++ b/hw/ppc/spapr_cpu_core.c
@@ -126,12 +126,23 @@ static void spapr_core_release(DeviceState *dev, void *opaque)
 void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
                        Error **errp)
 {
+    sPAPRMachineState *spapr = SPAPR_MACHINE(OBJECT(hotplug_dev));
     CPUCore *cc = CPU_CORE(dev);
     sPAPRDRConnector *drc =
         spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, cc->core_id);
     sPAPRDRConnectorClass *drck;
     Error *local_err = NULL;
+    int smt = kvmppc_smt_threads();
+    int index = cc->core_id / smt;
+    int spapr_max_cores = max_cpus / smp_threads;
+    int i;
 
+    for (i = spapr_max_cores - 1; i > index; i--) {
+        if (spapr->cores[i]) {
+            error_setg(errp, "core-id %d should be removed first", i * smt);
+            return;
+        }
+    }
     g_assert(drc);
 
     drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
@@ -214,7 +225,7 @@ void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
     sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(OBJECT(hotplug_dev));
     sPAPRMachineState *spapr = SPAPR_MACHINE(OBJECT(hotplug_dev));
     int spapr_max_cores = max_cpus / smp_threads;
-    int index;
+    int index, i;
     int smt = kvmppc_smt_threads();
     Error *local_err = NULL;
     CPUCore *cc = CPU_CORE(dev);
@@ -252,6 +263,14 @@ void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
         goto out;
     }
 
+    for (i = 0; i < index; i++) {
+        if (!spapr->cores[i]) {
+            error_setg(&local_err, "core-id %d should be added first",
+                       i * smt);
+            goto out;
+        }
+    }
+
 out:
     g_free(base_core_type);
     error_propagate(errp, local_err);