kho: check if kho is finalized in __kho_preserve_order()

Patch series "kho: add support for preserving vmalloc allocations", v5.

Following the discussion about preservation of memfd with LUO [1] these
patches add support for preserving vmalloc allocations.

Any KHO uses case presumes that there's a data structure that lists
physical addresses of preserved folios (and potentially some additional
metadata). Allowing vmalloc preservations with KHO allows scalable
preservation of such data structures.

For instance, instead of allocating array describing preserved folios in
the fdt, memfd preservation can use vmalloc:

preserved_folios = vmalloc_array(nr_folios, sizeof(*preserved_folios));
memfd_luo_preserve_folios(preserved_folios, folios, nr_folios);
kho_preserve_vmalloc(preserved_folios, &folios_info);


This patch (of 4):

Instead of checking if kho is finalized in each caller of
__kho_preserve_order(), do it in the core function itself.

Link: https://lkml.kernel.org/r/20250921054458.4043761-1-rppt@kernel.org
Link: https://lkml.kernel.org/r/20250921054458.4043761-2-rppt@kernel.org
Link: https://lore.kernel.org/all/20250807014442.3829950-30-pasha.tatashin@soleen.com [1]
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>