+ mm-userfaultfd-recheck-wp-registration-in-the-hugetlb-uffdio_copy-retry.patch added to mm-new branch

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

The patch titled
     Subject: mm/userfaultfd: recheck WP registration in the hugetlb UFFDIO_COPY retry
has been added to the -mm mm-new branch.  Its filename is
     mm-userfaultfd-recheck-wp-registration-in-the-hugetlb-uffdio_copy-retry.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-userfaultfd-recheck-wp-registration-in-the-hugetlb-uffdio_copy-retry.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Jose A. Perez de Azpillaga" <azpijr@gmail.com>
Subject: mm/userfaultfd: recheck WP registration in the hugetlb UFFDIO_COPY retry
Date: Tue, 03 Nov 2026 11:28:35 +0100

Patch series "mm/userfaultfd: recheck WP registration in the hugetlb
UFFDIO_COPY retry", v3.

The urgent fixes made hugetlb_fault() tolerate uffd bits left in VMAs
that are no longer registered for them, and asked for follow-ups that
remove the sources [1]. This is one: a hugetlb UFFDIO_COPY_MODE_WP copy
that has to fault in its source page doesn't recheck the WP registration
before retrying, so re-registering the range without WP in that window
leaves a uffd-wp PTE behind.

Patch 1 adds the missing check. Patch 2 adds a uffd-unit-tests case for
it, which fails on hugetlb without patch 1.

The other source 6/10 of [1] mentions, UFFDIO_COPY in MODE_WP racing
with UFFDIO_UNREGISTER [2], is closed by "mm/userfaultfd: write-lock the
VMA before waking waiters when unregistering" [3].

Based on mm-unstable.

Tested on x86_64 in QEMU.


This patch (of 2):

mfill_atomic_hugetlb() drops its locks to copy the source page with page
faults enabled and then looks the VMA up again. The retry doesn't check
that the VMA is still registered for WP, so if the range is re-registered
without WP in that window, a UFFDIO_COPY_MODE_WP copy installs a uffd-wp
PTE in a VMA without VM_UFFD_WP.

Recheck VM_UFFD_WP for UFFDIO_COPY_MODE_WP copies after looking the VMA
up again, and fail with -EINVAL if it is gone.

Link: https://lore.kernel.org/20261103102840.68903-1-azpijr@gmail.com
Link: https://lore.kernel.org/20261103102840.68903-2-azpijr@gmail.com
Link: https://lore.kernel.org/20261015-urgent_fixes-v1-0-42796911043b@kernel.org [1]
Link: https://lore.kernel.org/20261015-urgent_fixes-v1-6-42796911043b@kernel.org [2]
Link: https://lore.kernel.org/20261031-fixes_core-v3-23-d6437171ecc3@kernel.org [3] (in linux-next)
Link: https://lore.kernel.org/sashiko-outbox-194303@kernel.org [4]
Fixes: 6041c6917903 ("mm/hugetlb: take care of UFFDIO_COPY_MODE_WP")
Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
---

 mm/userfaultfd.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/userfaultfd.c~mm-userfaultfd-recheck-wp-registration-in-the-hugetlb-uffdio_copy-retry
+++ a/mm/userfaultfd.c
@@ -810,6 +810,10 @@ retry:
 		if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
 			goto out_unlock_vma;
 
+		/* The range may have been re-registered without WP meanwhile. */
+		if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP))
+			goto out_unlock_vma;
+
 		/*
 		 * If memory mappings are changing because of non-cooperative
 		 * operation (e.g. mremap) running in parallel, bail out and
_

Patches currently in -mm which might be from azpijr@gmail.com are

mm-userfaultfd-recheck-wp-registration-in-the-hugetlb-uffdio_copy-retry.patch
selftests-mm-add-a-uffd-test-for-re-registering-during-uffdio_copy.patch