* + mm-generalize-handling-of-userfaults-in-__do_fault.patch added to mm-unstable branch
@ 2026-03-30 19:44 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-03-30 19:44 UTC (permalink / raw)
To: mm-commits, peterx, akpm
The patch titled
Subject: mm: generalize handling of userfaults in __do_fault()
has been added to the -mm mm-unstable branch. Its filename is
mm-generalize-handling-of-userfaults-in-__do_fault.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-generalize-handling-of-userfaults-in-__do_fault.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Peter Xu <peterx@redhat.com>
Subject: mm: generalize handling of userfaults in __do_fault()
Date: Mon, 30 Mar 2026 13:11:13 +0300
When a VMA is registered with userfaulfd, its ->fault() method should
check if a folio exists in the page cache and call handle_userfault() with
appropriate mode:
- VM_UFFD_MINOR if VMA is registered in minor mode and the folio exists
- VM_UFFD_MISSING if VMA is registered in missing mode and the folio
does not exist
Instead of calling handle_userfault() directly from a specific ->fault()
handler, call __do_userfault() helper from the generic __do_fault().
For VMAs registered with userfaultfd the new __do_userfault() helper will
check if the folio is found in the page cache using
vm_uffd_ops->get_folio_noalloc() and call handle_userfault() with the
appropriate mode.
Make vm_uffd_ops->get_folio_noalloc() required method for non-anonymous
VMAs mapped at PTE level.
Link: https://lkml.kernel.org/r/20260330101116.1117699-13-rppt@kernel.org
Signed-off-by: Peter Xu <peterx@redhat.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrei Vagin <avagin@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nikita Kalyazin <kalyazin@amazon.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/memory.c | 43 +++++++++++++++++++++++++++++++++++++++++++
mm/shmem.c | 12 ------------
mm/userfaultfd.c | 9 +++++++++
3 files changed, 52 insertions(+), 12 deletions(-)
--- a/mm/memory.c~mm-generalize-handling-of-userfaults-in-__do_fault
+++ a/mm/memory.c
@@ -5423,6 +5423,41 @@ oom:
return VM_FAULT_OOM;
}
+#ifdef CONFIG_USERFAULTFD
+static vm_fault_t __do_userfault(struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ struct inode *inode;
+ struct folio *folio;
+
+ if (!(userfaultfd_missing(vma) || userfaultfd_minor(vma)))
+ return 0;
+
+ inode = file_inode(vma->vm_file);
+ folio = vma->vm_ops->uffd_ops->get_folio_noalloc(inode, vmf->pgoff);
+ if (!IS_ERR_OR_NULL(folio)) {
+ /*
+ * TODO: provide a flag for get_folio_noalloc() to avoid
+ * locking (or even the extra reference?)
+ */
+ folio_unlock(folio);
+ folio_put(folio);
+ if (userfaultfd_minor(vma))
+ return handle_userfault(vmf, VM_UFFD_MINOR);
+ } else {
+ if (userfaultfd_missing(vma))
+ return handle_userfault(vmf, VM_UFFD_MISSING);
+ }
+
+ return 0;
+}
+#else
+static inline vm_fault_t __do_userfault(struct vm_fault *vmf)
+{
+ return 0;
+}
+#endif
+
/*
* The mmap_lock must have been held on entry, and may have been
* released depending on flags and vma->vm_ops->fault() return value.
@@ -5455,6 +5490,14 @@ static vm_fault_t __do_fault(struct vm_f
return VM_FAULT_OOM;
}
+ /*
+ * If this is a userfault trap, process it in advance before
+ * triggering the genuine fault handler.
+ */
+ ret = __do_userfault(vmf);
+ if (ret)
+ return ret;
+
ret = vma->vm_ops->fault(vmf);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY |
VM_FAULT_DONE_COW)))
--- a/mm/shmem.c~mm-generalize-handling-of-userfaults-in-__do_fault
+++ a/mm/shmem.c
@@ -2483,13 +2483,6 @@ repeat:
fault_mm = vma ? vma->vm_mm : NULL;
folio = filemap_get_entry(inode->i_mapping, index);
- if (folio && vma && userfaultfd_minor(vma)) {
- if (!xa_is_value(folio))
- folio_put(folio);
- *fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
- return 0;
- }
-
if (xa_is_value(folio)) {
error = shmem_swapin_folio(inode, index, &folio,
sgp, gfp, vma, fault_type);
@@ -2534,11 +2527,6 @@ repeat:
* Fast cache lookup and swap lookup did not find it: allocate.
*/
- if (vma && userfaultfd_missing(vma)) {
- *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
- return 0;
- }
-
/* Find hugepage orders that are allowed for anonymous shmem and tmpfs. */
orders = shmem_allowable_huge_orders(inode, vma, index, write_end, false);
if (orders > 0) {
--- a/mm/userfaultfd.c~mm-generalize-handling-of-userfaults-in-__do_fault
+++ a/mm/userfaultfd.c
@@ -2046,6 +2046,15 @@ bool vma_can_userfault(struct vm_area_st
!vma_is_anonymous(vma))
return false;
+ /*
+ * File backed VMAs (except HugeTLB) must implement
+ * ops->get_folio_noalloc() because it's required by __do_userfault()
+ * in page fault handling.
+ */
+ if (!vma_is_anonymous(vma) && !is_vm_hugetlb_page(vma) &&
+ !ops->get_folio_noalloc)
+ return false;
+
return ops->can_userfault(vma, vm_flags);
}
_
Patches currently in -mm which might be from peterx@redhat.com are
mm-generalize-handling-of-userfaults-in-__do_fault.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
* + mm-generalize-handling-of-userfaults-in-__do_fault.patch added to mm-unstable branch
@ 2026-04-02 4:37 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-04-02 4:37 UTC (permalink / raw)
To: mm-commits, peterx, akpm
The patch titled
Subject: mm: generalize handling of userfaults in __do_fault()
has been added to the -mm mm-unstable branch. Its filename is
mm-generalize-handling-of-userfaults-in-__do_fault.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-generalize-handling-of-userfaults-in-__do_fault.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Peter Xu <peterx@redhat.com>
Subject: mm: generalize handling of userfaults in __do_fault()
Date: Thu, 2 Apr 2026 07:11:53 +0300
When a VMA is registered with userfaulfd, its ->fault() method should
check if a folio exists in the page cache and call handle_userfault() with
appropriate mode:
- VM_UFFD_MINOR if VMA is registered in minor mode and the folio exists
- VM_UFFD_MISSING if VMA is registered in missing mode and the folio
does not exist
Instead of calling handle_userfault() directly from a specific ->fault()
handler, call __do_userfault() helper from the generic __do_fault().
For VMAs registered with userfaultfd the new __do_userfault() helper will
check if the folio is found in the page cache using
vm_uffd_ops->get_folio_noalloc() and call handle_userfault() with the
appropriate mode.
Make vm_uffd_ops->get_folio_noalloc() required method for non-anonymous
VMAs mapped at PTE level.
Link: https://lkml.kernel.org/r/20260402041156.1377214-13-rppt@kernel.org
Signed-off-by: Peter Xu <peterx@redhat.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrei Vagin <avagin@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Harry Yoo (Oracle) <harry@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nikita Kalyazin <kalyazin@amazon.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/memory.c | 43 +++++++++++++++++++++++++++++++++++++++++++
mm/shmem.c | 12 ------------
mm/userfaultfd.c | 9 +++++++++
3 files changed, 52 insertions(+), 12 deletions(-)
--- a/mm/memory.c~mm-generalize-handling-of-userfaults-in-__do_fault
+++ a/mm/memory.c
@@ -5423,6 +5423,41 @@ oom:
return VM_FAULT_OOM;
}
+#ifdef CONFIG_USERFAULTFD
+static vm_fault_t __do_userfault(struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ struct inode *inode;
+ struct folio *folio;
+
+ if (!(userfaultfd_missing(vma) || userfaultfd_minor(vma)))
+ return 0;
+
+ inode = file_inode(vma->vm_file);
+ folio = vma->vm_ops->uffd_ops->get_folio_noalloc(inode, vmf->pgoff);
+ if (!IS_ERR_OR_NULL(folio)) {
+ /*
+ * TODO: provide a flag for get_folio_noalloc() to avoid
+ * locking (or even the extra reference?)
+ */
+ folio_unlock(folio);
+ folio_put(folio);
+ if (userfaultfd_minor(vma))
+ return handle_userfault(vmf, VM_UFFD_MINOR);
+ } else {
+ if (userfaultfd_missing(vma))
+ return handle_userfault(vmf, VM_UFFD_MISSING);
+ }
+
+ return 0;
+}
+#else
+static inline vm_fault_t __do_userfault(struct vm_fault *vmf)
+{
+ return 0;
+}
+#endif
+
/*
* The mmap_lock must have been held on entry, and may have been
* released depending on flags and vma->vm_ops->fault() return value.
@@ -5455,6 +5490,14 @@ static vm_fault_t __do_fault(struct vm_f
return VM_FAULT_OOM;
}
+ /*
+ * If this is a userfault trap, process it in advance before
+ * triggering the genuine fault handler.
+ */
+ ret = __do_userfault(vmf);
+ if (ret)
+ return ret;
+
ret = vma->vm_ops->fault(vmf);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY |
VM_FAULT_DONE_COW)))
--- a/mm/shmem.c~mm-generalize-handling-of-userfaults-in-__do_fault
+++ a/mm/shmem.c
@@ -2483,13 +2483,6 @@ repeat:
fault_mm = vma ? vma->vm_mm : NULL;
folio = filemap_get_entry(inode->i_mapping, index);
- if (folio && vma && userfaultfd_minor(vma)) {
- if (!xa_is_value(folio))
- folio_put(folio);
- *fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
- return 0;
- }
-
if (xa_is_value(folio)) {
error = shmem_swapin_folio(inode, index, &folio,
sgp, gfp, vma, fault_type);
@@ -2534,11 +2527,6 @@ repeat:
* Fast cache lookup and swap lookup did not find it: allocate.
*/
- if (vma && userfaultfd_missing(vma)) {
- *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
- return 0;
- }
-
/* Find hugepage orders that are allowed for anonymous shmem and tmpfs. */
orders = shmem_allowable_huge_orders(inode, vma, index, write_end, false);
if (orders > 0) {
--- a/mm/userfaultfd.c~mm-generalize-handling-of-userfaults-in-__do_fault
+++ a/mm/userfaultfd.c
@@ -2046,6 +2046,15 @@ bool vma_can_userfault(struct vm_area_st
!vma_is_anonymous(vma))
return false;
+ /*
+ * File backed VMAs (except HugeTLB) must implement
+ * ops->get_folio_noalloc() because it's required by __do_userfault()
+ * in page fault handling.
+ */
+ if (!vma_is_anonymous(vma) && !is_vm_hugetlb_page(vma) &&
+ !ops->get_folio_noalloc)
+ return false;
+
return ops->can_userfault(vma, vm_flags);
}
_
Patches currently in -mm which might be from peterx@redhat.com are
mm-generalize-handling-of-userfaults-in-__do_fault.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-04-02 4:37 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-04-02 4:37 + mm-generalize-handling-of-userfaults-in-__do_fault.patch added to mm-unstable branch Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2026-03-30 19:44 Andrew Morton
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox