powerpc/numa: Add ability to disable and debug topology updates

We have hit a few customer issues with the topology update code (VPHN
and PRRN). It would be nice to be able to debug the notifications coming
from the hypervisor in both cases to the LPAR, as well as to disable
responding to the notifications at boot-time, to narrow down the source
of the problems. Add a basic level of such functionality, similar to the
numa= command-line parameter. We already have a toggle in
/proc/powerpc/topology_updates that allows run-time enabling/disabling,
so the updates can be started at run-time if desired. But the bugs we've
run into have occured during boot or very shortly after coming to login,
and have resulted in a broken NUMA topology.

Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 10d51c2f10d7..c536e1c74320 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3370,6 +3370,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         e.g. base its process migration decisions on it.
                         Default is on.
 
+        topology_updates= [KNL, PPC, NUMA]
+                        Format: {off}
+                        Specify if the kernel should ignore (off)
+                        topology updates sent by the hypervisor to this
+                        LPAR.
+
         tp720=          [HW,PS2]
 
         tpm_suspend_pcr=[HW,TPM]