The patch titled Subject: mm/userfaultfd: Allow hugetlb change protection upon poison entry has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-userfaultfd-allow-hugetlb-change-protection-upon-poison-entry.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-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/userfaultfd: Allow hugetlb change protection upon poison entry Date: Fri, 5 Apr 2024 19:19:20 -0400
After UFFDIO_POISON, there can be two kinds of hugetlb pte markers, either the POISON one or UFFD_WP one.
Allow change protection to run on a poisoned marker just like !hugetlb cases, ignoring the marker irrelevant of the permission.
Here the two bits are mutual exclusive. For example, when install a poisoned entry it must not be UFFD_WP already (by checking pte_none() before such install). And it also means if UFFD_WP is set there must have no POISON bit set. It makes sense because UFFD_WP is a bit to reflect permission, and permissions do not apply if the pte is poisoned and destined to sigbus.
So here we simply check uffd_wp bit set first, do nothing otherwise.
Attach the Fixes to UFFDIO_POISON work, as before that it should not be possible to have poison entry for hugetlb (e.g., hugetlb doesn't do swap, so no chance of swapin errors).
Link: https://lkml.kernel.org/r/20240405231920.1772199-1-peterx@redhat.com Link: https://lore.kernel.org/r/000000000000920d5e0615602dd1@google.com Reported-by: syzbot+b07c8ac8eee3d4d8440f@syzkaller.appspotmail.com Fixes: fc71884a5f59 ("mm: userfaultfd: add new UFFDIO_POISON ioctl") Signed-off-by: Peter Xu peterx@redhat.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: David Hildenbrand david@redhat.com Cc: stable@vger.kernel.org [6.6+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/hugetlb.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/hugetlb.c~mm-userfaultfd-allow-hugetlb-change-protection-upon-poison-entry +++ a/mm/hugetlb.c @@ -7044,9 +7044,13 @@ long hugetlb_change_protection(struct vm if (!pte_same(pte, newpte)) set_huge_pte_at(mm, address, ptep, newpte, psize); } else if (unlikely(is_pte_marker(pte))) { - /* No other markers apply for now. */ - WARN_ON_ONCE(!pte_marker_uffd_wp(pte)); - if (uffd_wp_resolve) + /* + * Do nothing on a poison marker; page is + * corrupted, permissons do not apply. Here + * pte_marker_uffd_wp()==true implies !poison + * because they're mutual exclusive. + */ + if (pte_marker_uffd_wp(pte) && uffd_wp_resolve) /* Safe to modify directly (non-present->none). */ huge_pte_clear(mm, address, ptep, psize); } else if (!huge_pte_none(pte)) { _
Patches currently in -mm which might be from peterx@redhat.com are
mm-userfaultfd-allow-hugetlb-change-protection-upon-poison-entry.patch mm-hmm-process-pud-swap-entry-without-pud_huge.patch mm-gup-cache-p4d-in-follow_p4d_mask.patch mm-gup-check-p4d-presence-before-going-on.patch mm-x86-change-pxd_huge-behavior-to-exclude-swap-entries.patch mm-sparc-change-pxd_huge-behavior-to-exclude-swap-entries.patch mm-arm-use-macros-to-define-pmd-pud-helpers.patch mm-arm-redefine-pmd_huge-with-pmd_leaf.patch mm-arm64-merge-pxd_huge-and-pxd_leaf-definitions.patch mm-powerpc-redefine-pxd_huge-with-pxd_leaf.patch mm-gup-merge-pxd-huge-mapping-checks.patch mm-treewide-replace-pxd_huge-with-pxd_leaf.patch mm-treewide-remove-pxd_huge.patch mm-arm-remove-pmd_thp_or_huge.patch mm-document-pxd_leaf-api.patch selftests-mm-run_vmtestssh-fix-hugetlb-mem-size-calculation.patch selftests-mm-run_vmtestssh-fix-hugetlb-mem-size-calculation-fix.patch mm-kconfig-config_pgtable_has_huge_leaves.patch mm-hugetlb-declare-hugetlbfs_pagecache_present-non-static.patch mm-make-hpage_pxd_-macros-even-if-thp.patch mm-introduce-vma_pgtable_walk_beginend.patch mm-arch-provide-pud_pfn-fallback.patch mm-arch-provide-pud_pfn-fallback-fix.patch mm-gup-drop-folio_fast_pin_allowed-in-hugepd-processing.patch mm-gup-refactor-record_subpages-to-find-1st-small-page.patch mm-gup-handle-hugetlb-for-no_page_table.patch mm-gup-cache-pudp-in-follow_pud_mask.patch mm-gup-handle-huge-pud-for-follow_pud_mask.patch mm-gup-handle-huge-pmd-for-follow_pmd_mask.patch mm-gup-handle-huge-pmd-for-follow_pmd_mask-fix.patch mm-gup-handle-hugepd-for-follow_page.patch mm-gup-handle-hugetlb-in-the-generic-follow_page_mask-code.patch mm-allow-anon-exclusive-check-over-hugetlb-tail-pages.patch