The patch titled
Subject: mm/rmap: keep mapcount untouched for device-exclusive entries
has been added to the -mm mm-unstable branch. Its filename is
mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/rmap: keep mapcount untouched for device-exclusive entries
Date: Mon, 10 Feb 2025 20:37:58 +0100
Now that conversion to device-exclusive does no longer perform an rmap
walk and all page_vma_mapped_walk() users were taught to properly handle
device-exclusive entries, let's treat device-exclusive entries just as if
they would be present, similar to how we handle device-private entries
already.
This fixes swapout/migration/split/hwpoison of folios with
device-exclusive entries.
We only had to take care of page_vma_mapped_walk() users, because these
traditionally assume pte_present(). Other page table walkers already have
to handle !pte_present(), and some of them might simply skip them (e.g.,
MADV_PAGEOUT) if they are not specialized on them. This change doesn't
modify the latter.
Note that while folios with device-exclusive PTEs can now get migrated,
khugepaged will not collapse a THP if there is device-exclusive PTE.
Doing so might also not be desired if the device frequently performs
atomics to the same page. Similarly, KSM will never merge order-0 folios
that are device-exclusive.
Link: https://lkml.kernel.org/r/20250210193801.781278-17-david@xxxxxxxxxx
Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Alex Shi <alexs@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Karol Herbst <kherbst@xxxxxxxxxx>
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Lyude <lyude@xxxxxxxxxx>
Cc: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Simona Vetter <simona.vetter@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yanteng Si <si.yanteng@xxxxxxxxx>
Cc: Barry Song <v-songbaohua@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 17 +----------------
mm/rmap.c | 7 -------
2 files changed, 1 insertion(+), 23 deletions(-)
--- a/mm/memory.c~mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries
+++ a/mm/memory.c
@@ -743,20 +743,6 @@ static void restore_exclusive_pte(struct
VM_BUG_ON_FOLIO(pte_write(pte) && (!folio_test_anon(folio) &&
PageAnonExclusive(page)), folio);
-
- /*
- * No need to take a page reference as one was already
- * created when the swap entry was made.
- */
- if (folio_test_anon(folio))
- folio_add_anon_rmap_pte(folio, page, vma, address, RMAP_NONE);
- else
- /*
- * Currently device exclusive access only supports anonymous
- * memory so the entry shouldn't point to a filebacked page.
- */
- WARN_ON_ONCE(1);
-
set_pte_at(vma->vm_mm, address, ptep, pte);
/*
@@ -1628,8 +1614,7 @@ static inline int zap_nonpresent_ptes(st
*/
WARN_ON_ONCE(!vma_is_anonymous(vma));
rss[mm_counter(folio)]--;
- if (is_device_private_entry(entry))
- folio_remove_rmap_pte(folio, page, vma);
+ folio_remove_rmap_pte(folio, page, vma);
folio_put(folio);
} else if (!non_swap_entry(entry)) {
/* Genuine swap entries, hence a private anon pages */
--- a/mm/rmap.c~mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries
+++ a/mm/rmap.c
@@ -2511,13 +2511,6 @@ struct page *make_device_exclusive(struc
/* The pte is writable, uffd-wp does not apply. */
set_pte_at(mm, addr, fw.ptep, swp_pte);
- /*
- * TODO: The device-exclusive PFN swap PTE holds a folio reference but
- * does not count as a mapping (mapcount), which is wrong and must be
- * fixed, otherwise RMAP walks don't behave as expected.
- */
- folio_remove_rmap_pte(folio, page, vma);
-
folio_walk_end(&fw, vma);
mmu_notifier_invalidate_range_end(&range);
*foliop = folio;
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-gup-reject-foll_split_pmd-with-hugetlb-vmas.patch
mm-rmap-reject-hugetlb-folios-in-folio_make_device_exclusive.patch
mm-rmap-convert-make_device_exclusive_range-to-make_device_exclusive.patch
mm-rmap-implement-make_device_exclusive-using-folio_walk-instead-of-rmap-walk.patch
mm-memory-detect-writability-in-restore_exclusive_pte-through-can_change_pte_writable.patch
mm-use-single-swp_device_exclusive-entry-type.patch
mm-page_vma_mapped-device-exclusive-entries-are-not-migration-entries.patch
kernel-events-uprobes-handle-device-exclusive-entries-correctly-in-__replace_page.patch
mm-ksm-handle-device-exclusive-entries-correctly-in-write_protect_page.patch
mm-rmap-handle-device-exclusive-entries-correctly-in-try_to_unmap_one.patch
mm-rmap-handle-device-exclusive-entries-correctly-in-try_to_migrate_one.patch
mm-rmap-handle-device-exclusive-entries-correctly-in-page_vma_mkclean_one.patch
mm-page_idle-handle-device-exclusive-entries-correctly-in-page_idle_clear_pte_refs_one.patch
mm-damon-handle-device-exclusive-entries-correctly-in-damon_folio_young_one.patch
mm-damon-handle-device-exclusive-entries-correctly-in-damon_folio_mkold_one.patch
mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch
mm-rmap-avoid-ebusy-from-make_device_exclusive.patch
