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Message-ID: <20260127192936.1250096-10-rppt@kernel.org>
Date: Tue, 27 Jan 2026 21:29:28 +0200
From: Mike Rapoport <rppt@...nel.org>
To: linux-mm@...ck.org
Cc: Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
David Hildenbrand <david@...hat.com>,
Hugh Dickins <hughd@...gle.com>,
James Houghton <jthoughton@...gle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Michal Hocko <mhocko@...e.com>,
Mike Rapoport <rppt@...nel.org>,
Muchun Song <muchun.song@...ux.dev>,
Nikita Kalyazin <kalyazin@...zon.com>,
Oscar Salvador <osalvador@...e.de>,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Xu <peterx@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Shuah Khan <shuah@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
linux-kernel@...r.kernel.org,
kvm@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH RFC 09/17] userfaultfd: introduce vm_uffd_ops->alloc_folio()
From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
and use it to refactor mfill_atomic_pte_zeroed_folio() and
mfill_atomic_pte_copy().
mfill_atomic_pte_zeroed_folio() and mfill_atomic_pte_copy() perform
almost identical actions:
* allocate a folio
* update folio contents (either copy from userspace of fill with zeros)
* update page tables with the new folio
Split a __mfill_atomic_pte() helper that handles both cases and uses
newly introduced vm_uffd_ops->alloc_folio() to allocate the folio.
Pass the ops structure from the callers to __mfill_atomic_pte() to later
allow using anon_uffd_ops for MAP_PRIVATE mappings of file-backed VMAs.
Note, that the new ops method is called alloc_folio() rather than
folio_alloc() to avoid clash with alloc_tag macro folio_alloc().
Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
include/linux/userfaultfd_k.h | 6 +++
mm/userfaultfd.c | 92 ++++++++++++++++++-----------------
2 files changed, 54 insertions(+), 44 deletions(-)
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 66dfc3c164e6..4d8b879eed91 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -91,6 +91,12 @@ struct vm_uffd_ops {
* The returned folio is locked and with reference held.
*/
struct folio *(*get_folio_noalloc)(struct inode *inode, pgoff_t pgoff);
+ /*
+ * Called during resolution of UFFDIO_COPY request.
+ * Should return allocate a and return folio or NULL if allocation fails.
+ */
+ struct folio *(*alloc_folio)(struct vm_area_struct *vma,
+ unsigned long addr);
};
/* A combined operation mode + behavior flags. */
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index f0e6336015f1..b3c12630769c 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -42,8 +42,26 @@ static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags)
return true;
}
+static struct folio *anon_alloc_folio(struct vm_area_struct *vma,
+ unsigned long addr)
+{
+ struct folio *folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma,
+ addr);
+
+ if (!folio)
+ return NULL;
+
+ if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) {
+ folio_put(folio);
+ return NULL;
+ }
+
+ return folio;
+}
+
static const struct vm_uffd_ops anon_uffd_ops = {
.can_userfault = anon_can_userfault,
+ .alloc_folio = anon_alloc_folio,
};
static const struct vm_uffd_ops *vma_uffd_ops(struct vm_area_struct *vma)
@@ -455,7 +473,8 @@ static int mfill_copy_folio_retry(struct mfill_state *state, struct folio *folio
return 0;
}
-static int mfill_atomic_pte_copy(struct mfill_state *state)
+static int __mfill_atomic_pte(struct mfill_state *state,
+ const struct vm_uffd_ops *ops)
{
unsigned long dst_addr = state->dst_addr;
unsigned long src_addr = state->src_addr;
@@ -463,20 +482,22 @@ static int mfill_atomic_pte_copy(struct mfill_state *state)
struct folio *folio;
int ret;
- folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, state->vma, dst_addr);
+ folio = ops->alloc_folio(state->vma, state->dst_addr);
if (!folio)
return -ENOMEM;
- ret = -ENOMEM;
- if (mem_cgroup_charge(folio, state->vma->vm_mm, GFP_KERNEL))
- goto out_release;
-
- ret = mfill_copy_folio_locked(folio, src_addr);
- if (unlikely(ret)) {
+ if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) {
+ ret = mfill_copy_folio_locked(folio, src_addr);
/* fallback to copy_from_user outside mmap_lock */
- ret = mfill_copy_folio_retry(state, folio);
- if (ret)
- goto out_release;
+ if (unlikely(ret)) {
+ ret = mfill_copy_folio_retry(state, folio);
+ if (ret)
+ goto err_folio_put;
+ }
+ } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
+ clear_user_highpage(&folio->page, state->dst_addr);
+ } else {
+ VM_WARN_ONCE(1, "unknown UFFDIO operation");
}
/*
@@ -489,47 +510,30 @@ static int mfill_atomic_pte_copy(struct mfill_state *state)
ret = mfill_atomic_install_pte(state->pmd, state->vma, dst_addr,
&folio->page, true, flags);
if (ret)
- goto out_release;
-out:
- return ret;
-out_release:
+ goto err_folio_put;
+
+ return 0;
+
+err_folio_put:
+ folio_put(folio);
/* Don't return -ENOENT so that our caller won't retry */
if (ret == -ENOENT)
ret = -EFAULT;
- folio_put(folio);
- goto out;
+ return ret;
}
-static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr)
+static int mfill_atomic_pte_copy(struct mfill_state *state)
{
- struct folio *folio;
- int ret = -ENOMEM;
-
- folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr);
- if (!folio)
- return ret;
-
- if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
- goto out_put;
+ const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);
- /*
- * The memory barrier inside __folio_mark_uptodate makes sure that
- * zeroing out the folio become visible before mapping the page
- * using set_pte_at(). See do_anonymous_page().
- */
- __folio_mark_uptodate(folio);
+ return __mfill_atomic_pte(state, ops);
+}
- ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
- &folio->page, true, 0);
- if (ret)
- goto out_put;
+static int mfill_atomic_pte_zeroed_folio(struct mfill_state *state)
+{
+ const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);
- return 0;
-out_put:
- folio_put(folio);
- return ret;
+ return __mfill_atomic_pte(state, ops);
}
static int mfill_atomic_pte_zeropage(struct mfill_state *state)
@@ -542,7 +546,7 @@ static int mfill_atomic_pte_zeropage(struct mfill_state *state)
int ret;
if (mm_forbids_zeropage(dst_vma->vm_mm))
- return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);
+ return mfill_atomic_pte_zeroed_folio(state);
_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
dst_vma->vm_page_prot));
--
2.51.0
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