Commit 022a12de authored by Balbir Singh's avatar Balbir Singh Committed by Andrew Morton
Browse files

mm/migrate_device: handle partially mapped folios during collection 

Extend migrate_vma_collect_pmd() to handle partially mapped large folios
that require splitting before migration can proceed.

During PTE walk in the collection phase, if a large folio is only
partially mapped in the migration range, it must be split to ensure the
folio is correctly migrated.

[matthew.brost@intel.com: handle partially mapped folios during split]
  Link: https://lkml.kernel.org/r/20251120230825.181072-1-matthew.brost@intel.com
Link: https://lkml.kernel.org/r/20251001065707.920170-7-balbirs@nvidia.com


Signed-off-by: default avatarBalbir Singh <balbirs@nvidia.com>
Signed-off-by: default avatarMatthew Brost <matthew.brost@intel.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: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 14628729

mm/migrate_device.c

+69 −1
Original line number Diff line number Diff line
@@ -54,6 +54,55 @@ static int migrate_vma_collect_hole(unsigned long start, 
	return 0;

}



/**

 * migrate_vma_split_folio() - Helper function to split a THP folio

 * @folio: the folio to split

 * @fault_page: struct page associated with the fault if any

 *

 * Returns 0 on success

 */

static int migrate_vma_split_folio(struct folio *folio,

				   struct page *fault_page)

{

	int ret;

	struct folio *fault_folio = fault_page ? page_folio(fault_page) : NULL;

	struct folio *new_fault_folio = NULL;



	if (folio != fault_folio) {

		folio_get(folio);

		folio_lock(folio);

	}



	ret = split_folio(folio);

	if (ret) {

		if (folio != fault_folio) {

			folio_unlock(folio);

			folio_put(folio);

		}

		return ret;

	}



	new_fault_folio = fault_page ? page_folio(fault_page) : NULL;



	/*

	 * Ensure the lock is held on the correct

	 * folio after the split

	 */

	if (!new_fault_folio) {

		folio_unlock(folio);

		folio_put(folio);

	} else if (folio != new_fault_folio) {

		if (new_fault_folio != fault_folio) {

			folio_get(new_fault_folio);

			folio_lock(new_fault_folio);

		}

		folio_unlock(folio);

		folio_put(folio);

	}



	return 0;

}



static int migrate_vma_collect_pmd(pmd_t *pmdp,

				   unsigned long start,

				   unsigned long end,
@@ -107,10 +156,11 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, 
		}

	}



	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);

	ptep = pte_offset_map_lock(mm, pmdp, start, &ptl);

	if (!ptep)

		goto again;

	arch_enter_lazy_mmu_mode();

	ptep += (addr - start) / PAGE_SIZE;



	for (; addr < end; addr += PAGE_SIZE, ptep++) {

		struct dev_pagemap *pgmap;
@@ -171,6 +221,24 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, 
					pgmap->owner != migrate->pgmap_owner)

					goto next;

			}

			folio = page ? page_folio(page) : NULL;

			if (folio && folio_test_large(folio)) {

				int ret;



				arch_leave_lazy_mmu_mode();

				pte_unmap_unlock(ptep, ptl);

				ret = migrate_vma_split_folio(folio,

							  migrate->fault_page);



				if (ret) {

					if (unmapped)

						flush_tlb_range(walk->vma, start, end);



					return migrate_vma_collect_skip(addr, end, walk);

				}



				goto again;

			}

			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;

			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;

		}