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.
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: David Hildenbrand <da...@redhat.com>
Cc: Zi Yan <z...@nvidia.com>
Cc: Joshua Hahn <joshua.hah...@gmail.com>
Cc: Rakie Kim <rakie....@sk.com>
Cc: Byungchul Park <byungc...@sk.com>
Cc: Gregory Price <gou...@gourry.net>
Cc: Ying Huang <ying.hu...@linux.alibaba.com>
Cc: Alistair Popple <apop...@nvidia.com>
Cc: Oscar Salvador <osalva...@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
Cc: Baolin Wang <baolin.w...@linux.alibaba.com>
Cc: "Liam R. Howlett" <liam.howl...@oracle.com>
Cc: Nico Pache <npa...@redhat.com>
Cc: Ryan Roberts <ryan.robe...@arm.com>
Cc: Dev Jain <dev.j...@arm.com>
Cc: Barry Song <bao...@kernel.org>
Cc: Lyude Paul <ly...@redhat.com>
Cc: Danilo Krummrich <d...@kernel.org>
Cc: David Airlie <airl...@gmail.com>
Cc: Simona Vetter <sim...@ffwll.ch>
Cc: Ralph Campbell <rcampb...@nvidia.com>
Cc: Mika Penttilä <mpent...@redhat.com>
Cc: Matthew Brost <matthew.br...@intel.com>
Cc: Francois Dugast <francois.dug...@intel.com>
Signed-off-by: Balbir Singh <balb...@nvidia.com>
---
mm/migrate_device.c | 95 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 95 insertions(+)
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index e05e14d6eacd..e58c3f9d01c8 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -54,6 +54,54 @@ static int migrate_vma_collect_hole(unsigned long start,
return 0;
}
+/**
+ * migrate_vma_split_folio - Helper function to split a(n) (m)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) {
+ 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,
@@ -136,6 +184,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
* page table entry. Other special swap entries are not
* migratable, and we ignore regular swapped page.
*/
+ struct folio *folio;
+
entry = pte_to_swp_entry(pte);
if (!is_device_private_entry(entry))
goto next;
@@ -147,6 +197,29 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
pgmap->owner != migrate->pgmap_owner)
goto next;
+ folio = page_folio(page);
+ if (folio_test_large(folio)) {
+ int ret;
+
+ /*
+ * The reason for finding pmd present with a
+ * large folio for the pte is partial unmaps.
+ * Split the folio now for the migration to be
+ * handled correctly
+ */
+ pte_unmap_unlock(ptep, ptl);
+ ret = migrate_vma_split_folio(folio,
+ migrate->fault_page);
+
+ if (ret) {
+ ptep = pte_offset_map_lock(mm, pmdp,
addr, &ptl);
+ goto next;
+ }
+
+ addr = start;
+ goto again;
+ }
+
mpfn = migrate_pfn(page_to_pfn(page)) |
MIGRATE_PFN_MIGRATE;
if (is_writable_device_private_entry(entry))
@@ -171,6 +244,28 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
pgmap->owner != migrate->pgmap_owner)
goto next;
}
+ folio = page_folio(page);
+ if (folio_test_large(folio)) {
+ int ret;
+
+ /*
+ * The reason for finding pmd present with a
+ * large folio for the pte is partial unmaps.
+ * Split the folio now for the migration to be
+ * handled correctly
+ */
+ pte_unmap_unlock(ptep, ptl);
+ ret = migrate_vma_split_folio(folio,
+ migrate->fault_page);
+
+ if (ret) {
+ ptep = pte_offset_map_lock(mm, pmdp,
addr, &ptl);
+ goto next;
+ }
+
+ addr = start;
+ goto again;
+ }
mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
}
--
2.50.1
