powerpc/pseries: Disable CPU hotplug across migrations

[Michael Ellerman]

On Mon, 2018-09-17 at 19:14:02 UTC, Nathan Fontenot wrote:
> When performing partition migrations all present CPUs must be online
> as all present CPUs must make the H_JOIN call as part of the migration
> process. Once all present CPUs make the H_JOIN call, one CPU is returned
> to make the rtas call to perform the migration to the destination system.
> 
> During testing of migration and changing the SMT state we have found
> instances where CPUs are offlined, as part of the SMT state change,
> before they make the H_JOIN call. This results in a hung system where
> every CPU is either in H_JOIN or offline.
> 
> To prevent this this patch disables CPU hotplug during the migration
> process.
> 
> Signed-off-by: Nathan Fontenot <nfont at linux.vnet.ibm.com>
> Reviewed-by: Tyrel Datwyler <tyreld at linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/85a88cabad57d26d826dd94ea34d3a

cheers