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Message-ID: <20250903011900.3657435-3-balbirs@nvidia.com>
Date: Wed, 3 Sep 2025 11:18:47 +1000
From: Balbir Singh <balbirs@...dia.com>
To: linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Cc: damon@...ts.linux.dev,
dri-devel@...ts.freedesktop.org,
Balbir Singh <balbirs@...dia.com>,
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>,
Matthew Brost <matthew.brost@...el.com>,
Francois Dugast <francois.dugast@...el.com>
Subject: [v4 02/15] mm/huge_memory: add device-private THP support to PMD operations
Extend core huge page management functions to handle device-private THP
entries. This enables proper handling of large device-private folios in
fundamental MM operations.
The following functions have been updated:
- copy_huge_pmd(): Handle device-private entries during fork/clone
- zap_huge_pmd(): Properly free device-private THP during munmap
- change_huge_pmd(): Support protection changes on device-private THP
- __pte_offset_map(): Add device-private entry awareness
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: Matthew Brost <matthew.brost@...el.com>
Cc: Francois Dugast <francois.dugast@...el.com>
Signed-off-by: Matthew Brost <matthew.brost@...el.com>
Signed-off-by: Balbir Singh <balbirs@...dia.com>
---
include/linux/swapops.h | 27 +++++++++++++++++++
mm/huge_memory.c | 60 ++++++++++++++++++++++++++++++++++++-----
mm/pgtable-generic.c | 6 +++++
3 files changed, 86 insertions(+), 7 deletions(-)
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 64ea151a7ae3..59c5889a4d54 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -594,6 +594,33 @@ static inline int is_pmd_migration_entry(pmd_t pmd)
}
#endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */
+#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_ARCH_ENABLE_THP_MIGRATION)
+
+/**
+ * is_pmd_device_private_entry() - Check if PMD contains a device private swap entry
+ * @pmd: The PMD to check
+ *
+ * Returns true if the PMD contains a swap entry that represents a device private
+ * page mapping. This is used for zone device private pages that have been
+ * swapped out but still need special handling during various memory management
+ * operations.
+ *
+ * Return: 1 if PMD contains device private entry, 0 otherwise
+ */
+static inline int is_pmd_device_private_entry(pmd_t pmd)
+{
+ return is_swap_pmd(pmd) && is_device_private_entry(pmd_to_swp_entry(pmd));
+}
+
+#else /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */
+
+static inline int is_pmd_device_private_entry(pmd_t pmd)
+{
+ return 0;
+}
+
+#endif /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */
+
static inline int non_swap_entry(swp_entry_t entry)
{
return swp_type(entry) >= MAX_SWAPFILES;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9c38a95e9f09..4acdedf84fe6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1711,8 +1711,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
if (unlikely(is_swap_pmd(pmd))) {
swp_entry_t entry = pmd_to_swp_entry(pmd);
- VM_BUG_ON(!is_pmd_migration_entry(pmd));
- if (!is_readable_migration_entry(entry)) {
+ VM_WARN_ON(!is_pmd_migration_entry(pmd) &&
+ !is_pmd_device_private_entry(pmd));
+
+ if (is_migration_entry(entry) &&
+ !is_readable_migration_entry(entry)) {
entry = make_readable_migration_entry(
swp_offset(entry));
pmd = swp_entry_to_pmd(entry);
@@ -1721,7 +1724,37 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
if (pmd_swp_uffd_wp(*src_pmd))
pmd = pmd_swp_mkuffd_wp(pmd);
set_pmd_at(src_mm, addr, src_pmd, pmd);
+ } else if (is_device_private_entry(entry)) {
+ /*
+ * For device private entries, since there are no
+ * read exclusive entries, writable = !readable
+ */
+ if (is_writable_device_private_entry(entry)) {
+ entry = make_readable_device_private_entry(
+ swp_offset(entry));
+ pmd = swp_entry_to_pmd(entry);
+
+ if (pmd_swp_soft_dirty(*src_pmd))
+ pmd = pmd_swp_mksoft_dirty(pmd);
+ if (pmd_swp_uffd_wp(*src_pmd))
+ pmd = pmd_swp_mkuffd_wp(pmd);
+ set_pmd_at(src_mm, addr, src_pmd, pmd);
+ }
+
+ src_folio = pfn_swap_entry_folio(entry);
+ VM_WARN_ON(!folio_test_large(src_folio));
+
+ folio_get(src_folio);
+ /*
+ * folio_try_dup_anon_rmap_pmd does not fail for
+ * device private entries.
+ */
+ ret = folio_try_dup_anon_rmap_pmd(src_folio,
+ &src_folio->page,
+ dst_vma, src_vma);
+ VM_WARN_ON(ret);
}
+
add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
mm_inc_nr_ptes(dst_mm);
pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
@@ -2219,15 +2252,17 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
folio_remove_rmap_pmd(folio, page, vma);
WARN_ON_ONCE(folio_mapcount(folio) < 0);
VM_BUG_ON_PAGE(!PageHead(page), page);
- } else if (thp_migration_supported()) {
+ } else if (is_pmd_migration_entry(orig_pmd) ||
+ is_pmd_device_private_entry(orig_pmd)) {
swp_entry_t entry;
- VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
entry = pmd_to_swp_entry(orig_pmd);
folio = pfn_swap_entry_folio(entry);
flush_needed = 0;
- } else
- WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
+
+ if (!thp_migration_supported())
+ WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
+ }
if (folio_test_anon(folio)) {
zap_deposited_table(tlb->mm, pmd);
@@ -2247,6 +2282,12 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
folio_mark_accessed(folio);
}
+ if (folio_is_device_private(folio)) {
+ folio_remove_rmap_pmd(folio, &folio->page, vma);
+ WARN_ON_ONCE(folio_mapcount(folio) < 0);
+ folio_put(folio);
+ }
+
spin_unlock(ptl);
if (flush_needed)
tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
@@ -2375,7 +2416,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
struct folio *folio = pfn_swap_entry_folio(entry);
pmd_t newpmd;
- VM_BUG_ON(!is_pmd_migration_entry(*pmd));
+ VM_WARN_ON(!is_pmd_migration_entry(*pmd) &&
+ !folio_is_device_private(folio));
if (is_writable_migration_entry(entry)) {
/*
* A protection check is difficult so
@@ -2388,6 +2430,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
newpmd = swp_entry_to_pmd(entry);
if (pmd_swp_soft_dirty(*pmd))
newpmd = pmd_swp_mksoft_dirty(newpmd);
+ } else if (is_writable_device_private_entry(entry)) {
+ entry = make_readable_device_private_entry(
+ swp_offset(entry));
+ newpmd = swp_entry_to_pmd(entry);
} else {
newpmd = *pmd;
}
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index 567e2d084071..604e8206a2ec 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -292,6 +292,12 @@ pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)
*pmdvalp = pmdval;
if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval)))
goto nomap;
+ if (is_swap_pmd(pmdval)) {
+ swp_entry_t entry = pmd_to_swp_entry(pmdval);
+
+ if (is_device_private_entry(entry))
+ goto nomap;
+ }
if (unlikely(pmd_trans_huge(pmdval)))
goto nomap;
if (unlikely(pmd_bad(pmdval))) {
--
2.50.1
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