powerpc/pseries: Perform full re-add of CPU for topology update post-migration

On pseries systems, performing a partition migration can result in
altering the nodes a CPU is assigned to on the destination system. For
exampl, pre-migration on the source system CPUs are in node 1 and 3,
post-migration on the destination system CPUs are in nodes 2 and 3.

Handling the node change for a CPU can cause corruption in the slab
cache if we hit a timing where a CPUs node is changed while cache_reap()
is invoked. The corruption occurs because the slab cache code appears
to rely on the CPU and slab cache pages being on the same node.

The current dynamic updating of a CPUs node done in arch/powerpc/mm/numa.c
does not prevent us from hitting this scenario.

Changing the device tree property update notification handler that
recognizes an affinity change for a CPU to do a full DLPAR remove and
add of the CPU instead of dynamically changing its node resolves this
issue.
Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Michael W. Bringmann <mwb@linux.vnet.ibm.com>
Tested-by: Michael W. Bringmann <mwb@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/topology.h

@@ -132,6 +132,8 @@ static inline void shared_proc_topology_init(void) {}
 #define topology_sibling_cpumask(cpu)	(per_cpu(cpu_sibling_map, cpu))
 #define topology_core_cpumask(cpu)	(per_cpu(cpu_core_map, cpu))
 #define topology_core_id(cpu)		(cpu_to_core_id(cpu))
+
+int dlpar_cpu_readd(int cpu);
 #endif
 #endif
 

arch/powerpc/mm/numa.c

@@ -1460,13 +1460,6 @@ static void reset_topology_timer(void)
 
 #ifdef CONFIG_SMP
 
-static void stage_topology_update(int core_id)
-{
-	cpumask_or(&cpu_associativity_changes_mask,
-		&cpu_associativity_changes_mask, cpu_sibling_mask(core_id));
-	reset_topology_timer();
-}
-
 static int dt_update_callback(struct notifier_block *nb,
 				unsigned long action, void *data)
 {
@@ -1479,7 +1472,7 @@ static int dt_update_callback(struct notifier_block *nb,
 		    !of_prop_cmp(update->prop->name, "ibm,associativity")) {
 			u32 core_id;
 			of_property_read_u32(update->dn, "reg", &core_id);
-			stage_topology_update(core_id);
+			rc = dlpar_cpu_readd(core_id);
 			rc = NOTIFY_OK;
 		}
 		break;

arch/powerpc/platforms/pseries/hotplug-cpu.c

@@ -802,6 +802,25 @@ static int dlpar_cpu_add_by_count(u32 cpus_to_add)
 	return rc;
 }
 
+int dlpar_cpu_readd(int cpu)
+{
+	struct device_node *dn;
+	struct device *dev;
+	u32 drc_index;
+	int rc;
+
+	dev = get_cpu_device(cpu);
+	dn = dev->of_node;
+
+	rc = of_property_read_u32(dn, "ibm,my-drc-index", &drc_index);
+
+	rc = dlpar_cpu_remove_by_index(drc_index);
+	if (!rc)
+		rc = dlpar_cpu_add(drc_index);
+
+	return rc;
+}
+
 int dlpar_cpu(struct pseries_hp_errorlog *hp_elog)
 {
 	u32 count, drc_index;