On Thu, 29 Apr 2021 19:49:08 +0200, Laurent Dufour wrote:

When a CPU is hot added, the CPU ids are taken from the available mask from
the lower possible set. If that set of values was previously used for CPU
attached to a different node, this seems to application like if these CPUs
have migrated from a node to another one which is not expected in real
life.

To prevent this, it is needed to record the CPU ids used for each node and
to not reuse them on another node. However, to prevent CPU hot plug to
fail, in the case the CPU ids is starved on a node, the capability to reuse
other nodes’ free CPU ids is kept. A warning is displayed in such a case
to warn the user.

[...]

Applied to powerpc/next.

[1/1] pseries: prevent free CPU ids to be reused on another node
      https://git.kernel.org/powerpc/c/bd1dd4c5f5286df0148b5b316f37c583b8f55fa1

cheers