linux-kernel - [PATCH v2 2/2] fixup: mm/migrate_device: add THP splitting during migration

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Message-Id: <20251120230825.181072-2-matthew.brost@intel.com>
Date: Thu, 20 Nov 2025 15:08:25 -0800
From: Matthew Brost <matthew.brost@...el.com>
To: linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Zi Yan <ziy@...dia.com>,
	Joshua Hahn <joshua.hahnjy@...il.com>,
	Rakie Kim <rakie.kim@...com>,
	Byungchul Park <byungchul@...com>,
	Gregory Price <gourry@...rry.net>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Alistair Popple <apopple@...dia.com>,
	Oscar Salvador <osalvador@...e.de>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...nel.org>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Ralph Campbell <rcampbell@...dia.com>,
	Mika Penttilä <mpenttil@...hat.com>,
	Francois Dugast <francois.dugast@...el.com>,
	Balbir Singh <balbirs@...dia.com>
Subject: [PATCH v2 2/2] fixup: mm/migrate_device: add THP splitting during migration

Fix splitting a folio in PMD collection to collect a skip on folio split
failure and continue the loop at the current position on success. This
fixes an issue where migration entries that had already been collected
could accidentally be left behind.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>
Cc: Zi Yan <ziy@...dia.com>
Cc: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: Rakie Kim <rakie.kim@...com>
Cc: Byungchul Park <byungchul@...com>
Cc: Gregory Price <gourry@...rry.net>
Cc: Ying Huang <ying.huang@...ux.alibaba.com>
Cc: Alistair Popple <apopple@...dia.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: Nico Pache <npache@...hat.com>
Cc: Ryan Roberts <ryan.roberts@....com>
Cc: Dev Jain <dev.jain@....com>
Cc: Barry Song <baohua@...nel.org>
Cc: Lyude Paul <lyude@...hat.com>
Cc: Danilo Krummrich <dakr@...nel.org>
Cc: David Airlie <airlied@...il.com>
Cc: Simona Vetter <simona@...ll.ch>
Cc: Ralph Campbell <rcampbell@...dia.com>
Cc: Mika Penttilä <mpenttil@...hat.com>
Cc: Francois Dugast <francois.dugast@...el.com>
Cc: Balbir Singh <balbirs@...dia.com>
Signed-off-by: Matthew Brost <matthew.brost@...el.com>

---
This fixup should be squashed into the patch "mm/migrate_device: add THP
splitting during migration" in mm/mm-unstable
---
 mm/migrate_device.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 4506e96dcd20..ab373fd38961 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -313,16 +313,18 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			if (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) {
-					ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
-					goto next;
+					if (unmapped)
+						flush_tlb_range(walk->vma, start, end);
+
+					return migrate_vma_collect_skip(addr, end, walk);
 				}

-				addr = start;
 				goto again;
 			}

-- 
2.34.1