linux-kernel - [PATCH] mm/huge_memory: softleaf device private fixes in remove_migration

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Message-ID: <20251112044634.963360-2-balbirs@nvidia.com>
Date: Wed, 12 Nov 2025 15:46:34 +1100
From: Balbir Singh <balbirs@...dia.com>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	Balbir Singh <balbirs@...dia.com>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Zi Yan <ziy@...dia.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>,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH] mm/huge_memory: softleaf device private fixes in remove_migration_pmd()

commit a6ca2ba46390 ("mm: replace pmd_to_swp_entry() with softleaf_from_pmd()")
does not work with device private THP entries. softleaf_is_migration_young()
asserts that the entry be a migration entry, but in the current code, the
entry might already be replaced by a device private entry by the time the
check is made. The issue exists with commit
7385dbdbf841 ("mm/rmap: extend rmap and migration support device-private entries")

Fix this by processing the migration entries prior to conversion to
device private if the folio is device private.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...nel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Zi Yan <ziy@...dia.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: Lance Yang <lance.yang@...ux.dev>

Signed-off-by: Balbir Singh <balbirs@...dia.com>
---
 mm/huge_memory.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 942bd8410c54..82b019205216 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4939,6 +4939,7 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	unsigned long haddr = address & HPAGE_PMD_MASK;
 	pmd_t pmde;
 	softleaf_t entry;
+	bool old = false, dirty = false, migration_read_entry = false;
 
 	if (!(pvmw->pmd && !pvmw->pte))
 		return;
@@ -4947,6 +4948,19 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	folio_get(folio);
 	pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));
 
+	if (!softleaf_is_migration_young(entry))
+		old = true;
+
+	/* NOTE: this may contain setting soft-dirty on some archs */
+	if (folio_test_dirty(folio) && softleaf_is_migration_dirty(entry))
+		dirty = true;
+
+	if (softleaf_is_migration_write(entry))
+		pmde = pmd_mkwrite(pmde, vma);
+
+	if (!softleaf_is_migration_read(entry))
+		migration_read_entry = true;
+
 	if (folio_is_device_private(folio)) {
 		if (pmd_write(pmde))
 			entry = make_writable_device_private_entry(
@@ -4959,20 +4973,17 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 
 	if (pmd_swp_soft_dirty(*pvmw->pmd))
 		pmde = pmd_mksoft_dirty(pmde);
-	if (softleaf_is_migration_write(entry))
-		pmde = pmd_mkwrite(pmde, vma);
+	if (old)
+		pmde = pmd_mkold(pmde);
 	if (pmd_swp_uffd_wp(*pvmw->pmd))
 		pmde = pmd_mkuffd_wp(pmde);
-	if (!softleaf_is_migration_young(entry))
-		pmde = pmd_mkold(pmde);
-	/* NOTE: this may contain setting soft-dirty on some archs */
-	if (folio_test_dirty(folio) && softleaf_is_migration_dirty(entry))
+	if (dirty)
 		pmde = pmd_mkdirty(pmde);
 
 	if (folio_test_anon(folio)) {
 		rmap_t rmap_flags = RMAP_NONE;
 
-		if (!softleaf_is_migration_read(entry))
+		if (migration_read_entry)
 			rmap_flags |= RMAP_EXCLUSIVE;
 
 		folio_add_anon_rmap_pmd(folio, new, vma, haddr, rmap_flags);
-- 
2.51.1