[merged mm-stable] mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch removed from -mm tree

[merged mm-stable] mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/rmap: keep mapcount untouched for device-exclusive entries
has been removed from the -mm tree.  Its filename was
     mm-rmap-keep-mapcount-untouched-for-device-exclusive-entries.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
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@redhat.com
Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Signed-off-by: David Hildenbrand <david@redhat.com>
Tested-by: Alistair Popple <apopple@nvidia.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lyude <lyude@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yanteng Si <si.yanteng@linux.dev>
Cc: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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
@@ -741,20 +741,6 @@ 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);
 
 	/*
@@ -1626,8 +1612,7 @@ 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@redhat.com are

mm-factor-out-large-folio-handling-from-folio_order-into-folio_large_order.patch
mm-factor-out-large-folio-handling-from-folio_nr_pages-into-folio_large_nr_pages.patch
mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page.patch
mm-let-_folio_nr_pages-overlay-memcg_data-in-first-tail-page-fix.patch
mm-move-hugetlb-specific-things-in-folio-to-page.patch
mm-move-_pincount-in-folio-to-page-on-32bit.patch
mm-move-_entire_mapcount-in-folio-to-page-on-32bit.patch
mm-rmap-pass-dst_vma-to-folio_dup_file_rmap_pte-and-friends.patch
mm-rmap-pass-vma-to-__folio_add_rmap.patch
mm-rmap-abstract-large-mapcount-operations-for-large-folios-hugetlb.patch
bit_spinlock-__always_inline-unlock-functions.patch
mm-rmap-use-folio_large_nr_pages-in-add-remove-functions.patch
mm-rmap-basic-mm-owner-tracking-for-large-folios-hugetlb.patch
mm-copy-on-write-cow-reuse-support-for-pte-mapped-thp.patch
mm-convert-folio_likely_mapped_shared-to-folio_maybe_mapped_shared.patch
mm-config_no_page_mapcount-to-prepare-for-not-maintain-per-page-mapcounts-in-large-folios.patch
fs-proc-page-remove-per-page-mapcount-dependency-for-proc-kpagecount-config_no_page_mapcount.patch
fs-proc-task_mmu-remove-per-page-mapcount-dependency-for-pm_mmap_exclusive-config_no_page_mapcount.patch
fs-proc-task_mmu-remove-per-page-mapcount-dependency-for-mapmax-config_no_page_mapcount.patch
fs-proc-task_mmu-remove-per-page-mapcount-dependency-for-smaps-smaps_rollup-config_no_page_mapcount.patch
mm-stop-maintaining-the-per-page-mapcount-of-large-folios-config_no_page_mapcount.patch