lib/test_hmm: add zone device private THP test infrastructure

Enhance the hmm test driver (lib/test_hmm) with support for THP pages.

A new pool of free_folios() has now been added to the dmirror device,
which can be allocated when a request for a THP zone device private page
is made.

Add compound page awareness to the allocation function during normal
migration and fault based migration.  These routines also copy
folio_nr_pages() when moving data between system memory and device memory.

args.src and args.dst used to hold migration entries are now dynamically
allocated (as they need to hold HPAGE_PMD_NR entries or more).

Split and migrate support will be added in future patches in this series.

Link: https://lkml.kernel.org/r/20251001065707.920170-10-balbirs@nvidia.com
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memremap.h

@@ -177,6 +177,18 @@ static inline bool folio_is_pci_p2pdma(const struct folio *folio)
 		folio->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
 }
 
+static inline void *folio_zone_device_data(const struct folio *folio)
+{
+	VM_WARN_ON_FOLIO(!folio_is_device_private(folio), folio);
+	return folio->page.zone_device_data;
+}
+
+static inline void folio_set_zone_device_data(struct folio *folio, void *data)
+{
+	VM_WARN_ON_FOLIO(!folio_is_device_private(folio), folio);
+	folio->page.zone_device_data = data;
+}
+
 static inline bool is_pci_p2pdma_page(const struct page *page)
 {
 	return IS_ENABLED(CONFIG_PCI_P2PDMA) &&