selftests/mm: factor out hmm_buffer_alloc() to consolidate buffer setup

Each HMM test open-codes the same buffer initialization sequence: allocate
main buffer, assign file descriptor and size, allocate mirror buffer, then
perform mmap mapping.  Factor out this repeated logic into a standalone
hmm_buffer_alloc() helper to eliminate ~35 open-coded copies.

The new helper supports distinct mmap_size and mirror_size parameters to
fit scenarios with THP alignment padding or per-page snapshot flags.  It
also exposes prot, flags and fd arguments, enabling support for
MAP_SHARED, MAP_HUGETLB and file-backed mappings.

Eliminates ~360 lines of redundant boilerplate code.  Fixes a missing NULL
pointer check bug in the hmm_buffer_alloc() previously used only by the
migration benchmark, now subsumed by this new unified helper.

Link: https://lore.kernel.org/20260713033209.280435-1-lihongfu@kylinos.cn
Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions