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>

1 files changed, 19 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index 2f8e62163602..97feb6e79f1a 100644
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/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;