shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops

Add filemap_add() and filemap_remove() methods to vm_uffd_ops and use them
in __mfill_atomic_pte() to add shmem folios to page cache and remove them
in case of error.

Implement these methods in shmem along with vm_uffd_ops->alloc_folio() and
drop shmem_mfill_atomic_pte().

Since userfaultfd now does not reference any functions from shmem, drop
include if linux/shmem_fs.h from mm/userfaultfd.c

mfill_atomic_install_pte() is not used anywhere outside of mm/userfaultfd,
make it static.

Link: https://lore.kernel.org/20260402041156.1377214-11-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>
Cc: David Carlier <devnexen@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 14 insertions, 19 deletions

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index a8273b32e041..1a345142af7d 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -221,20 +221,6 @@ static inline pgoff_t shmem_fallocend(struct inode *inode, pgoff_t eof)
 
 extern bool shmem_charge(struct inode *inode, long pages);
 
-#ifdef CONFIG_USERFAULTFD
-#ifdef CONFIG_SHMEM
-extern int shmem_mfill_atomic_pte(pmd_t *dst_pmd,
-				  struct vm_area_struct *dst_vma,
-				  unsigned long dst_addr,
-				  unsigned long src_addr,
-				  uffd_flags_t flags,
-				  struct folio **foliop);
-#else /* !CONFIG_SHMEM */
-#define shmem_mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, \
-			       src_addr, flags, foliop) ({ BUG(); 0; })
-#endif /* CONFIG_SHMEM */
-#endif /* CONFIG_USERFAULTFD */
-
 /*
  * Used space is stored as unsigned 64-bit value in bytes but
  * quota core supports only signed 64-bit values so use that
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 0f508c752741..d2920f98ab86 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -100,6 +100,20 @@ struct vm_uffd_ops {
 	 */
 	struct folio *(*alloc_folio)(struct vm_area_struct *vma,
 				     unsigned long addr);
+	/*
+	 * Called during resolution of UFFDIO_COPY request.
+	 * Should only be called with a folio returned by alloc_folio() above.
+	 * The folio will be set to locked.
+	 * Returns 0 on success, error code on failure.
+	 */
+	int (*filemap_add)(struct folio *folio, struct vm_area_struct *vma,
+			 unsigned long addr);
+	/*
+	 * Called during resolution of UFFDIO_COPY request on the error
+	 * handling path.
+	 * Should revert the operation of ->filemap_add().
+	 */
+	void (*filemap_remove)(struct folio *folio, struct vm_area_struct *vma);
 };
 
 /* A combined operation mode + behavior flags. */
@@ -133,11 +147,6 @@ static inline uffd_flags_t uffd_flags_set_mode(uffd_flags_t flags, enum mfill_at
 /* Flags controlling behavior. These behavior changes are mode-independent. */
 #define MFILL_ATOMIC_WP MFILL_ATOMIC_FLAG(0)
 
-extern int mfill_atomic_install_pte(pmd_t *dst_pmd,
-				    struct vm_area_struct *dst_vma,
-				    unsigned long dst_addr, struct page *page,
-				    bool newly_allocated, uffd_flags_t flags);
-
 extern ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
 				 unsigned long src_start, unsigned long len,
 				 uffd_flags_t flags);