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mm/hugetlb: don't leave a uffd-wp marker when zapping an RWP entry

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An entry that is protected with UFFDIO_RWPROTECT is PAGE_NONE with the
uffd bit set, the bit that userfaultfd write protection uses too.  When
__unmap_hugepage_range() zaps an entry with that bit it leaves a
PTE_MARKER_UFFD_WP behind, whatever the VMA is registered for.

In a VMA registered with UFFDIO_REGISTER_MODE_RWP that marker means
nothing.  The next fault has hugetlb_no_page() turn it into a present,
read-only entry with the uffd bit.  That is not an RWP entry, since it is
not PAGE_NONE, and the VMA has no VM_UFFD_WP (the two modes can not be
registered together).  An earlier fix solved some side effects, now just
stop the zap from wrongly installing a marker.

Leave a marker only if the VMA is registered for write protection, both
for present and for non-present entries.  The zap of ordinary page
tables has the same test, in cond_install_uffd_wp_ptes(), and
hugetlb_change_protection() says that "uffd_rwp does not install markers".

After a zap the range of an RWP VMA is simply empty, as it is for
anonymous memory and shmem.  Nothing changes for VMAs with VM_UFFD_WP.  In
a VMA that is not registered at all a leftover uffd bit or marker is now
dropped by the zap and no longer kept alive.

Original fix generated by an LLM and sent in private by Josef.

[david@kernel.org: a bit of description overhaul+simplification]
Link: https://lore.kernel.org/20261015-urgent_fixes-v1-9-42796911043b@kernel.org
Fixes: 2d427bb016 ("mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP")
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Chris Mason <mason@kernel.org>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Adam Litke <agl@us.ibm.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: <stable@vger.kernel.org>
This commit is contained in:
Josef Bacik 2026-10-15 18:07:15 +02:00 committed by Andrew Morton
parent c37e9d9411
commit f6605fc6b1
1 changed files with 2 additions and 2 deletions
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4
mm/hugetlb.c
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@ -5309,7 +5309,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
* drop the uffd-wp bit in this zap, then replace the
* pte with a marker.
*/
if (pte_swp_uffd_any(pte) &&
if (userfaultfd_wp(vma) && pte_swp_uffd_any(pte) &&
!(zap_flags & ZAP_FLAG_DROP_MARKER))
set_huge_pte_at(mm, address, ptep,
make_pte_marker(PTE_MARKER_UFFD_WP),
@ -5345,7 +5345,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
if (huge_pte_dirty(pte))
folio_mark_dirty(folio);
/* Leave a uffd-wp pte marker if needed */
if (huge_pte_uffd(pte) &&
if (userfaultfd_wp(vma) && huge_pte_uffd(pte) &&
!(zap_flags & ZAP_FLAG_DROP_MARKER))
set_huge_pte_at(mm, address, ptep,
make_pte_marker(PTE_MARKER_UFFD_WP),