+ mm-hugetlb-fix-uffd-wp-bit-lost-when-unsharing-happens.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: mm/hugetlb: fix uffd-wp bit lost when unsharing happens
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb-fix-uffd-wp-bit-lost-when-unsharing-happens.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-uffd-wp-bit-lost-when-unsharing-happens.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: Peter Xu <peterx@redhat.com>
Subject: mm/hugetlb: fix uffd-wp bit lost when unsharing happens
Date: Mon, 17 Apr 2023 15:53:13 -0400

When we try to unshare a pinned page for a private hugetlb, uffd-wp bit
can get lost during unsharing.  Fix it by carrying it over.

This should be very rare, only if an unsharing happened on a private
hugetlb page with uffd-wp protected (e.g.  in a child which shares the
same page with parent with UFFD_FEATURE_EVENT_FORK enabled).

Link: https://lkml.kernel.org/r/20230417195317.898696-3-peterx@redhat.com
Fixes: 166f3ecc0daf ("mm/hugetlb: hook page faults for uffd write protection")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reported-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-fix-uffd-wp-bit-lost-when-unsharing-happens
+++ a/mm/hugetlb.c
@@ -5644,13 +5644,16 @@ retry_avoidcopy:
 	spin_lock(ptl);
 	ptep = hugetlb_walk(vma, haddr, huge_page_size(h));
 	if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) {
+		pte_t newpte = make_huge_pte(vma, &new_folio->page, !unshare);
+
 		/* Break COW or unshare */
 		huge_ptep_clear_flush(vma, haddr, ptep);
 		mmu_notifier_invalidate_range(mm, range.start, range.end);
 		page_remove_rmap(old_page, vma, true);
 		hugepage_add_new_anon_rmap(new_folio, vma, haddr);
-		set_huge_pte_at(mm, haddr, ptep,
-				make_huge_pte(vma, &new_folio->page, !unshare));
+		if (huge_pte_uffd_wp(pte))
+			newpte = huge_pte_mkuffd_wp(newpte);
+		set_huge_pte_at(mm, haddr, ptep, newpte);
 		folio_set_hugetlb_migratable(new_folio);
 		/* Make the old page be freed below */
 		new_folio = page_folio(old_page);
_

Patches currently in -mm which might be from peterx@redhat.com are

selftests-mm-update-gitignore-with-two-missing-tests.patch
selftests-mm-dump-a-summary-in-run_vmtestssh.patch
selftests-mm-merge-utilh-into-vm_utilh.patch
selftests-mm-use-test_gen_progs-where-proper.patch
selftests-mm-link-vm_utilc-always.patch
selftests-mm-merge-default_huge_page_size-into-one.patch
selftests-mm-use-pm_-macros-in-vm_utilsh.patch
selftests-mm-reuse-pagemap_get_entry-in-vm_utilh.patch
selftests-mm-test-uffdio_zeropage-only-when-hugetlb.patch
selftests-mm-drop-test_uffdio_zeropage_eexist.patch
selftests-mm-create-uffd-common.patch
selftests-mm-split-uffd-tests-into-uffd-stress-and-uffd-unit-tests.patch
selftests-mm-uffd_register.patch
selftests-mm-uffd_open_devsys.patch
selftests-mm-uffdio_api-test.patch
selftests-mm-drop-global-mem_fd-in-uffd-tests.patch
selftests-mm-drop-global-hpage_size-in-uffd-tests.patch
selftests-mm-rename-uffd_stats-to-uffd_args.patch
selftests-mm-let-uffd_handle_page_fault-take-wp-parameter.patch
selftests-mm-allow-allocate_area-to-fail-properly.patch
selftests-mm-add-framework-for-uffd-unit-test.patch
selftests-mm-move-uffd-pagemap-test-to-unit-test.patch
selftests-mm-move-uffd-minor-test-to-unit-test.patch
selftests-mm-move-uffd-sig-events-tests-into-uffd-unit-tests.patch
selftests-mm-move-zeropage-test-into-uffd-unit-tests.patch
selftests-mm-workaround-no-way-to-detect-uffd-minor-wp.patch
selftests-mm-allow-uffd-test-to-skip-properly-with-no-privilege.patch
selftests-mm-drop-sys-dev-test-in-uffd-stress-test.patch
selftests-mm-add-shmem-private-test-to-uffd-stress.patch
selftests-mm-add-uffdio-register-ioctls-test.patch
mm-hugetlb-fix-uffd-wp-during-fork.patch
mm-hugetlb-fix-uffd-wp-bit-lost-when-unsharing-happens.patch
selftests-mm-add-a-few-options-for-uffd-unit-test.patch
selftests-mm-extend-and-rename-uffd-pagemap-test.patch
selftests-mm-rename-cow_extra_libs-to-iouring_extra_libs.patch
selftests-mm-add-tests-for-ro-pinning-vs-fork.patch