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mm: handle VM_UFFD_RWP in khugepaged, rmap, and GUP

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Three mm paths outside the fault handler gate on the uffd PTE bit today:
khugepaged (skip collapse on ranges carrying markers), rmap (cap unmap
batching), and GUP (force a fault through gup_can_follow_protnone). 
Extend each to treat VM_UFFD_RWP the same as VM_UFFD_WP; otherwise per-PTE
RWP state is silently destroyed or bypassed.

khugepaged: try_collapse_pte_mapped_thp() and
file_backed_vma_is_retractable() already refuse to collapse or retract
page tables on ranges carrying the uffd PTE bit.  Broaden the VMA
predicate from userfaultfd_wp() to userfaultfd_protected() so VM_UFFD_RWP
ranges get the same protection.  hpage_collapse_scan_pmd() needs no change
— its existing pte_uffd() check already catches an RWP PTE because it
carries the uffd bit.

rmap: folio_unmap_pte_batch() caps batching at 1 for VM_UFFD_RWP so the
restore path handles each PTE with its own marker.

GUP: gup_can_follow_protnone() forces a fault on VM_UFFD_RWP VMAs
regardless of FOLL_HONOR_NUMA_FAULT.  RWP uses protnone as an
access-tracking marker, not for NUMA hinting, so any GUP — read or write
— must go through the userfaultfd fault path.

Link: https://lore.kernel.org/20260708111417.173443-9-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: James Houghton <jthoughton@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kiryl Shutsemau (Meta) 2026-07-08 12:14:09 +01:00 committed by Andrew Morton
parent 763f43865f
commit 7974c23853
3 changed files with 27 additions and 9 deletions
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16
include/linux/mm.h
View File

@ -4654,11 +4654,25 @@ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
/*
* Indicates whether GUP can follow a PROT_NONE mapped page, or whether
* a (NUMA hinting) fault is required.
* a (NUMA hinting or userfaultfd RWP) fault is required.
*/
static inline bool gup_can_follow_protnone(const struct vm_area_struct *vma,
unsigned int flags)
{
/*
* VM_UFFD_RWP uses protnone as an access-tracking marker, not for
* NUMA hinting. GUP must always take a fault so the access is
* delivered to userfaultfd, regardless of FOLL_HONOR_NUMA_FAULT.
*
* Only do so while the VMA is accessible. If it has been made
* inaccessible (e.g. mprotect(PROT_NONE)), fall through to the guard
* below: forcing a fault there would loop, as handle_mm_fault() makes
* no progress on protnone in an inaccessible VMA, and the access is
* denied regardless of RWP anyway.
*/
if (vma_test_single_mask(vma, VMA_UFFD_RWP) && vma_is_accessible(vma))
return false;
/*
* If callers don't want to honor NUMA hinting faults, no need to
* determine if we would actually have to trigger a NUMA hinting fault.

18
mm/khugepaged.c
View File

@ -1893,8 +1893,11 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign
if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER))
return SCAN_VMA_CHECK;
/* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
if (userfaultfd_wp(vma))
/*
* Keep pmd pgtable while the uffd bit is in use; see comment in
* retract_page_tables().
*/
if (userfaultfd_protected(vma))
return SCAN_PTE_UFFD;
folio = filemap_lock_folio(vma->vm_file->f_mapping,
@ -2107,13 +2110,14 @@ static bool file_backed_vma_is_retractable(struct vm_area_struct *vma)
return false;
/*
* When a vma is registered with uffd-wp, we cannot recycle
* When a vma is registered with uffd-wp or RWP, we cannot recycle
* the page table because there may be pte markers installed.
* Other vmas can still have the same file mapped hugely, but
* skip this one: it will always be mapped in small page size
* for uffd-wp registered ranges.
* VM_UFFD_RWP ranges similarly rely on per-PTE uffd state
* and cannot be recycled to a shared PMD. Other vmas can still
* have the same file mapped hugely, but skip this one: it will
* always be mapped in small page size for these registrations.
*/
if (userfaultfd_wp(vma))
if (userfaultfd_protected(vma))
return false;
/*

2
mm/rmap.c
View File

@ -1965,7 +1965,7 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
if (pte_unused(pte))
return 1;
if (userfaultfd_wp(vma))
if (userfaultfd_protected(vma))
return 1;
/*