kho: validate preserved memory map during population

kho: validate preserved memory map during population

If the previous kernel enabled KHO but did not call kho_finalize() (e.g.,
CONFIG_LIVEUPDATE=n or userspace skipped the finalization step), the
'preserved-memory-map' property in the FDT remains empty/zero.

Previously, kho_populate() would succeed regardless of the memory map's
state, reserving the incoming scratch regions in memblock.  However,
kho_memory_init() would later fail to deserialize the empty map.  By that
time, the scratch regions were already registered, leading to partial
initialization and subsequent list corruption (freeing scratch area twice)
during kho_init().

Move the validation of the preserved memory map earlier into
kho_populate(). If the memory map is empty/NULL:
1. Abort kho_populate() immediately with -ENOENT.
2. Do not register or reserve the incoming scratch memory, allowing the new
   kernel to reclaim those pages as standard free memory.
3. Leave the global 'kho_in' state uninitialized.

Consequently, kho_memory_init() sees no active KHO context
(kho_in.mem_chunks_phys is 0) and falls back to kho_reserve_scratch(),
allocating fresh scratch memory as if it were a standard cold boot.

Link: https://lkml.kernel.org/r/20251223140140.2090337-1-pasha.tatashin@soleen.com
Fixes: de51999e687c ("kho: allow memory preservation state updates after finalization")
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reported-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>