The quilt patch titled
Subject: mm/khugepaged: check again on anon uffd-wp during isolation
has been removed from the -mm tree. Its filename was
mm-khugepaged-check-again-on-anon-uffd-wp-during-isolation.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/khugepaged: check again on anon uffd-wp during isolation
Date: Wed, 5 Apr 2023 11:51:20 -0400
Khugepaged collapse an anonymous thp in two rounds of scans. The 2nd
round done in __collapse_huge_page_isolate() after
hpage_collapse_scan_pmd(), during which all the locks will be released
temporarily. It means the pgtable can change during this phase before 2nd
round starts.
It's logically possible some ptes got wr-protected during this phase, and
we can errornously collapse a thp without noticing some ptes are
wr-protected by userfault. e1e267c7928f wanted to avoid it but it only
did that for the 1st phase, not the 2nd phase.
Since __collapse_huge_page_isolate() happens after a round of small page
swapins, we don't need to worry on any !present ptes - if it existed
khugepaged will already bail out. So we only need to check present ptes
with uffd-wp bit set there.
This is something I found only but never had a reproducer, I thought it
was one caused a bug in Muhammad's recent pagemap new ioctl work, but it
turns out it's not the cause of that but an userspace bug. However this
seems to still be a real bug even with a very small race window, still
worth to have it fixed and copy stable.
Link: https://lkml.kernel.org/r/20230405155120.3608140-1-peterx@xxxxxxxxxx
Fixes: e1e267c7928f ("khugepaged: skip collapse if uffd-wp detected")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/mm/khugepaged.c~mm-khugepaged-check-again-on-anon-uffd-wp-during-isolation
+++ a/mm/khugepaged.c
@@ -573,6 +573,10 @@ static int __collapse_huge_page_isolate(
result = SCAN_PTE_NON_PRESENT;
goto out;
}
+ if (pte_uffd_wp(pteval)) {
+ result = SCAN_PTE_UFFD_WP;
+ goto out;
+ }
page = vm_normal_page(vma, address, pteval);
if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
result = SCAN_PAGE_NULL;
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx 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
