kho: allow memory preservation state updates after finalization

kho: allow memory preservation state updates after finalization

Currently, kho_preserve_* and kho_unpreserve_* return -EBUSY if KHO is
finalized.  This enforces a rigid "freeze" on the KHO memory state.

With the introduction of re-entrant finalization, this restriction is no
longer necessary.  Users should be allowed to modify the preservation set
(e.g., adding new pages or freeing old ones) even after an initial
finalization.

The intended workflow for updates is now:
1. Modify state (preserve/unpreserve).
2. Call kho_finalize() again to refresh the serialized metadata.

Remove the kho_out.finalized checks to enable this dynamic behavior.

This also allows to convert kho_unpreserve_* functions to void, as they do
not return any error anymore.

Link: https://lkml.kernel.org/r/20251114190002.3311679-13-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Coiby Xu <coxu@redhat.com>
Cc: Dave Vasilevsky <dave@vasilevsky.ca>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>