* + shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch added to mm-unstable branch
@ 2026-03-30 19:43 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-03-30 19:43 UTC (permalink / raw)
To: mm-commits, rppt, akpm
The patch titled
Subject: shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE
has been added to the -mm mm-unstable branch. Its filename is
shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.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: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Subject: shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE
Date: Mon, 30 Mar 2026 13:11:09 +0300
When userspace resolves a page fault in a shmem VMA with UFFDIO_CONTINUE
it needs to get a folio that already exists in the pagecache backing that
VMA.
Instead of using shmem_get_folio() for that, add a get_folio_noalloc()
method to 'struct vm_uffd_ops' that will return a folio if it exists in
the VMA's pagecache at given pgoff.
Implement get_folio_noalloc() method for shmem and slightly refactor
userfaultfd's mfill_get_vma() and mfill_atomic_pte_continue() to support
this new API.
Link: https://lkml.kernel.org/r/20260330101116.1117699-9-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: James Houghton <jthoughton@google.com>
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: 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: Peter Xu <peterx@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>
---
include/linux/userfaultfd_k.h | 7 ++++++
mm/shmem.c | 15 +++++++++++++-
mm/userfaultfd.c | 34 ++++++++++++++++----------------
3 files changed, 39 insertions(+), 17 deletions(-)
--- a/include/linux/userfaultfd_k.h~shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue
+++ a/include/linux/userfaultfd_k.h
@@ -87,6 +87,13 @@ extern vm_fault_t handle_userfault(struc
struct vm_uffd_ops {
/* Checks if a VMA can support userfaultfd */
bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags);
+ /*
+ * Called to resolve UFFDIO_CONTINUE request.
+ * Should return the folio found at pgoff in the VMA's pagecache if it
+ * exists or ERR_PTR otherwise.
+ * The returned folio is locked and with reference held.
+ */
+ struct folio *(*get_folio_noalloc)(struct inode *inode, pgoff_t pgoff);
};
/* A combined operation mode + behavior flags. */
--- a/mm/shmem.c~shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue
+++ a/mm/shmem.c
@@ -3289,13 +3289,26 @@ out_unacct_blocks:
return ret;
}
+static struct folio *shmem_get_folio_noalloc(struct inode *inode, pgoff_t pgoff)
+{
+ struct folio *folio;
+ int err;
+
+ err = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC);
+ if (err)
+ return ERR_PTR(err);
+
+ return folio;
+}
+
static bool shmem_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags)
{
return true;
}
static const struct vm_uffd_ops shmem_uffd_ops = {
- .can_userfault = shmem_can_userfault,
+ .can_userfault = shmem_can_userfault,
+ .get_folio_noalloc = shmem_get_folio_noalloc,
};
#endif /* CONFIG_USERFAULTFD */
--- a/mm/userfaultfd.c~shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue
+++ a/mm/userfaultfd.c
@@ -191,6 +191,7 @@ static int mfill_get_vma(struct mfill_st
struct userfaultfd_ctx *ctx = state->ctx;
uffd_flags_t flags = state->flags;
struct vm_area_struct *dst_vma;
+ const struct vm_uffd_ops *ops;
int err;
/*
@@ -232,10 +233,12 @@ static int mfill_get_vma(struct mfill_st
if (is_vm_hugetlb_page(dst_vma))
return 0;
- if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
+ ops = vma_uffd_ops(dst_vma);
+ if (!ops)
goto out_unlock;
- if (!vma_is_shmem(dst_vma) &&
- uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
+
+ if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) &&
+ !ops->get_folio_noalloc)
goto out_unlock;
return 0;
@@ -575,6 +578,7 @@ out:
static int mfill_atomic_pte_continue(struct mfill_state *state)
{
struct vm_area_struct *dst_vma = state->vma;
+ const struct vm_uffd_ops *ops = vma_uffd_ops(dst_vma);
unsigned long dst_addr = state->dst_addr;
pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
struct inode *inode = file_inode(dst_vma->vm_file);
@@ -584,17 +588,16 @@ static int mfill_atomic_pte_continue(str
struct page *page;
int ret;
- ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC);
- /* Our caller expects us to return -EFAULT if we failed to find folio */
- if (ret == -ENOENT)
- ret = -EFAULT;
- if (ret)
- goto out;
- if (!folio) {
- ret = -EFAULT;
- goto out;
+ if (!ops) {
+ VM_WARN_ONCE(1, "UFFDIO_CONTINUE for unsupported VMA");
+ return -EOPNOTSUPP;
}
+ folio = ops->get_folio_noalloc(inode, pgoff);
+ /* Our caller expects us to return -EFAULT if we failed to find folio */
+ if (IS_ERR_OR_NULL(folio))
+ return -EFAULT;
+
page = folio_file_page(folio, pgoff);
if (PageHWPoison(page)) {
ret = -EIO;
@@ -607,13 +610,12 @@ static int mfill_atomic_pte_continue(str
goto out_release;
folio_unlock(folio);
- ret = 0;
-out:
- return ret;
+ return 0;
+
out_release:
folio_unlock(folio);
folio_put(folio);
- goto out;
+ return ret;
}
/* Handles UFFDIO_POISON for all non-hugetlb VMAs. */
_
Patches currently in -mm which might be from rppt@kernel.org are
userfaultfd-introduce-mfill_copy_folio_locked-helper.patch
userfaultfd-introduce-struct-mfill_state.patch
userfaultfd-introduce-mfill_establish_pmd-helper.patch
userfaultfd-introduce-mfill_get_vma-and-mfill_put_vma.patch
userfaultfd-retry-copying-with-locks-dropped-in-mfill_atomic_pte_copy.patch
userfaultfd-move-vma_can_userfault-out-of-line.patch
userfaultfd-introduce-vm_uffd_ops.patch
shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch
userfaultfd-introduce-vm_uffd_ops-alloc_folio.patch
shmem-userfaultfd-implement-shmem-uffd-operations-using-vm_uffd_ops.patch
userfaultfd-mfill_atomic-remove-retry-logic.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
* + shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch added to mm-unstable branch
@ 2026-04-02 4:36 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-04-02 4:36 UTC (permalink / raw)
To: mm-commits, rppt, akpm
The patch titled
Subject: shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE
has been added to the -mm mm-unstable branch. Its filename is
shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.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: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Subject: shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE
Date: Thu, 2 Apr 2026 07:11:49 +0300
When userspace resolves a page fault in a shmem VMA with UFFDIO_CONTINUE
it needs to get a folio that already exists in the pagecache backing that
VMA.
Instead of using shmem_get_folio() for that, add a get_folio_noalloc()
method to 'struct vm_uffd_ops' that will return a folio if it exists in
the VMA's pagecache at given pgoff.
Implement get_folio_noalloc() method for shmem and slightly refactor
userfaultfd's mfill_get_vma() and mfill_atomic_pte_continue() to support
this new API.
Link: https://lkml.kernel.org/r/20260402041156.1377214-9-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: James Houghton <jthoughton@google.com>
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: 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: Peter Xu <peterx@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>
---
include/linux/userfaultfd_k.h | 7 ++++++
mm/shmem.c | 15 +++++++++++++-
mm/userfaultfd.c | 34 ++++++++++++++++----------------
3 files changed, 39 insertions(+), 17 deletions(-)
--- a/include/linux/userfaultfd_k.h~shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue
+++ a/include/linux/userfaultfd_k.h
@@ -87,6 +87,13 @@ extern vm_fault_t handle_userfault(struc
struct vm_uffd_ops {
/* Checks if a VMA can support userfaultfd */
bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags);
+ /*
+ * Called to resolve UFFDIO_CONTINUE request.
+ * Should return the folio found at pgoff in the VMA's pagecache if it
+ * exists or ERR_PTR otherwise.
+ * The returned folio is locked and with reference held.
+ */
+ struct folio *(*get_folio_noalloc)(struct inode *inode, pgoff_t pgoff);
};
/* A combined operation mode + behavior flags. */
--- a/mm/shmem.c~shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue
+++ a/mm/shmem.c
@@ -3289,13 +3289,26 @@ out_unacct_blocks:
return ret;
}
+static struct folio *shmem_get_folio_noalloc(struct inode *inode, pgoff_t pgoff)
+{
+ struct folio *folio;
+ int err;
+
+ err = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC);
+ if (err)
+ return ERR_PTR(err);
+
+ return folio;
+}
+
static bool shmem_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags)
{
return true;
}
static const struct vm_uffd_ops shmem_uffd_ops = {
- .can_userfault = shmem_can_userfault,
+ .can_userfault = shmem_can_userfault,
+ .get_folio_noalloc = shmem_get_folio_noalloc,
};
#endif /* CONFIG_USERFAULTFD */
--- a/mm/userfaultfd.c~shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue
+++ a/mm/userfaultfd.c
@@ -191,6 +191,7 @@ static int mfill_get_vma(struct mfill_st
struct userfaultfd_ctx *ctx = state->ctx;
uffd_flags_t flags = state->flags;
struct vm_area_struct *dst_vma;
+ const struct vm_uffd_ops *ops;
int err;
/*
@@ -232,10 +233,12 @@ static int mfill_get_vma(struct mfill_st
if (is_vm_hugetlb_page(dst_vma))
return 0;
- if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
+ ops = vma_uffd_ops(dst_vma);
+ if (!ops)
goto out_unlock;
- if (!vma_is_shmem(dst_vma) &&
- uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
+
+ if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) &&
+ !ops->get_folio_noalloc)
goto out_unlock;
return 0;
@@ -575,6 +578,7 @@ out:
static int mfill_atomic_pte_continue(struct mfill_state *state)
{
struct vm_area_struct *dst_vma = state->vma;
+ const struct vm_uffd_ops *ops = vma_uffd_ops(dst_vma);
unsigned long dst_addr = state->dst_addr;
pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
struct inode *inode = file_inode(dst_vma->vm_file);
@@ -584,17 +588,16 @@ static int mfill_atomic_pte_continue(str
struct page *page;
int ret;
- ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC);
- /* Our caller expects us to return -EFAULT if we failed to find folio */
- if (ret == -ENOENT)
- ret = -EFAULT;
- if (ret)
- goto out;
- if (!folio) {
- ret = -EFAULT;
- goto out;
+ if (!ops) {
+ VM_WARN_ONCE(1, "UFFDIO_CONTINUE for unsupported VMA");
+ return -EOPNOTSUPP;
}
+ folio = ops->get_folio_noalloc(inode, pgoff);
+ /* Our caller expects us to return -EFAULT if we failed to find folio */
+ if (IS_ERR_OR_NULL(folio))
+ return -EFAULT;
+
page = folio_file_page(folio, pgoff);
if (PageHWPoison(page)) {
ret = -EIO;
@@ -607,13 +610,12 @@ static int mfill_atomic_pte_continue(str
goto out_release;
folio_unlock(folio);
- ret = 0;
-out:
- return ret;
+ return 0;
+
out_release:
folio_unlock(folio);
folio_put(folio);
- goto out;
+ return ret;
}
/* Handles UFFDIO_POISON for all non-hugetlb VMAs. */
_
Patches currently in -mm which might be from rppt@kernel.org are
userfaultfd-introduce-mfill_copy_folio_locked-helper.patch
userfaultfd-introduce-struct-mfill_state.patch
userfaultfd-introduce-mfill_establish_pmd-helper.patch
userfaultfd-introduce-mfill_get_vma-and-mfill_put_vma.patch
userfaultfd-retry-copying-with-locks-dropped-in-mfill_atomic_pte_copy.patch
userfaultfd-move-vma_can_userfault-out-of-line.patch
userfaultfd-introduce-vm_uffd_ops.patch
shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch
userfaultfd-introduce-vm_uffd_ops-alloc_folio.patch
shmem-userfaultfd-implement-shmem-uffd-operations-using-vm_uffd_ops.patch
userfaultfd-mfill_atomic-remove-retry-logic.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
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