mm/rmap: extend rmap and migration support device-private entries

Add device-private THP support to reverse mapping infrastructure, enabling
proper handling during migration and walk operations.

The key changes are:
- add_migration_pmd()/remove_migration_pmd(): Handle device-private
  entries during folio migration and splitting
- page_vma_mapped_walk(): Recognize device-private THP entries during
  VMA traversal operations

This change supports folio splitting and migration operations on
device-private entries.

[[email protected]: fix override of entry in remove_migration_pmd]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: follow pattern used in remove_migration_pte()]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Balbir Singh <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Acked-by: Zi Yan <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: Ying Huang <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: "Liam R. Howlett" <[email protected]>
Cc: Nico Pache <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Simona Vetter <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Mika Penttilä <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Francois Dugast <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/damon/ops-common.c

@@ -75,12 +75,24 @@ void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr
 void damon_pmdp_mkold(pmd_t *pmd, struct vm_area_struct *vma, unsigned long addr)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct folio *folio = damon_get_folio(pmd_pfn(pmdp_get(pmd)));
+	pmd_t pmdval = pmdp_get(pmd);
+	struct folio *folio;
+	bool young = false;
+	unsigned long pfn;
 
+	if (likely(pmd_present(pmdval)))
+		pfn = pmd_pfn(pmdval);
+	else
+		pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
+
+	folio = damon_get_folio(pfn);
 	if (!folio)
 		return;
 
-	if (pmdp_clear_young_notify(vma, addr, pmd))
+	if (likely(pmd_present(pmdval)))
+		young |= pmdp_clear_young_notify(vma, addr, pmd);
+	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + HPAGE_PMD_SIZE);
+	if (young)
 		folio_set_young(folio);
 
 	folio_set_idle(folio);
@@ -199,7 +211,9 @@ static bool damon_folio_young_one(struct folio *folio,
 				mmu_notifier_test_young(vma->vm_mm, addr);
 		} else {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-			*accessed = pmd_young(pmdp_get(pvmw.pmd)) ||
+			pmd_t pmd = pmdp_get(pvmw.pmd);
+
+			*accessed = (pmd_present(pmd) && pmd_young(pmd)) ||
 				!folio_test_idle(folio) ||
 				mmu_notifier_test_young(vma->vm_mm, addr);
 #else

mm/huge_memory.c

@@ -4583,7 +4583,10 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
 		return 0;
 
 	flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
-	pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
+	if (unlikely(!pmd_present(*pvmw->pmd)))
+		pmdval = pmdp_huge_get_and_clear(vma->vm_mm, address, pvmw->pmd);
+	else
+		pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
 
 	/* See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */
 	anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(page);
@@ -4633,6 +4636,7 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	entry = pmd_to_swp_entry(*pvmw->pmd);
 	folio_get(folio);
 	pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));
+
 	if (pmd_swp_soft_dirty(*pvmw->pmd))
 		pmde = pmd_mksoft_dirty(pmde);
 	if (is_writable_migration_entry(entry))
@@ -4645,6 +4649,23 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	if (folio_test_dirty(folio) && is_migration_entry_dirty(entry))
 		pmde = pmd_mkdirty(pmde);
 
+	if (folio_is_device_private(folio)) {
+		swp_entry_t entry;
+
+		if (pmd_write(pmde))
+			entry = make_writable_device_private_entry(
+							page_to_pfn(new));
+		else
+			entry = make_readable_device_private_entry(
+							page_to_pfn(new));
+		pmde = swp_entry_to_pmd(entry);
+
+		if (pmd_swp_soft_dirty(*pvmw->pmd))
+			pmde = pmd_swp_mksoft_dirty(pmde);
+		if (pmd_swp_uffd_wp(*pvmw->pmd))
+			pmde = pmd_swp_mkuffd_wp(pmde);
+	}
+
 	if (folio_test_anon(folio)) {
 		rmap_t rmap_flags = RMAP_NONE;
 

mm/page_idle.c

@@ -71,8 +71,11 @@ static bool page_idle_clear_pte_refs_one(struct folio *folio,
 				referenced |= ptep_test_and_clear_young(vma, addr, pvmw.pte);
 			referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
 		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
-			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
-				referenced = true;
+			pmd_t pmdval = pmdp_get(pvmw.pmd);
+
+			if (likely(pmd_present(pmdval)))
+				referenced |= pmdp_clear_young_notify(vma, addr, pvmw.pmd);
+			referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PMD_SIZE);
 		} else {
 			/* unexpected pmd-mapped page? */
 			WARN_ON_ONCE(1);

mm/page_vma_mapped.c

@@ -277,6 +277,13 @@ restart:
 			 * cannot return prematurely, while zap_huge_pmd() has
 			 * cleared *pmd but not decremented compound_mapcount().
 			 */
+			swp_entry_t entry = pmd_to_swp_entry(pmde);
+
+			if (is_device_private_entry(entry)) {
+				pvmw->ptl = pmd_lock(mm, pvmw->pmd);
+				return true;
+			}
+
 			if ((pvmw->flags & PVMW_SYNC) &&
 			    thp_vma_suitable_order(vma, pvmw->address,
 						   PMD_ORDER) &&

mm/rmap.c

@@ -1022,9 +1022,16 @@ static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
 		} else {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 			pmd_t *pmd = pvmw->pmd;
-			pmd_t entry;
+			pmd_t entry = pmdp_get(pmd);
 
-			if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
+			/*
+			 * Please see the comment above (!pte_present).
+			 * A non present PMD is not writable from a CPU
+			 * perspective.
+			 */
+			if (!pmd_present(entry))
+				continue;
+			if (!pmd_dirty(entry) && !pmd_write(entry))
 				continue;
 
 			flush_cache_range(vma, address,
@@ -2319,6 +2326,9 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 	while (page_vma_mapped_walk(&pvmw)) {
 		/* PMD-mapped THP migration entry */
 		if (!pvmw.pte) {
+			__maybe_unused unsigned long pfn;
+			__maybe_unused pmd_t pmdval;
+
 			if (flags & TTU_SPLIT_HUGE_PMD) {
 				split_huge_pmd_locked(vma, pvmw.address,
 						      pvmw.pmd, true);
@@ -2327,8 +2337,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 				break;
 			}
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
-			subpage = folio_page(folio,
-				pmd_pfn(*pvmw.pmd) - folio_pfn(folio));
+			pmdval = pmdp_get(pvmw.pmd);
+			if (likely(pmd_present(pmdval)))
+				pfn = pmd_pfn(pmdval);
+			else
+				pfn = swp_offset_pfn(pmd_to_swp_entry(pmdval));
+
+			subpage = folio_page(folio, pfn - folio_pfn(folio));
+
 			VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
 					!folio_test_pmd_mappable(folio), folio);