From nobody Sun Feb 8 14:13:01 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90C09299922; Tue, 27 Jan 2026 19:30:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769542250; cv=none; b=lMTW+k4JbKJPC59gw7YttfLXK7aZsUbAVwBBuXGDFr4eaTyT6YXhW7PO3czYL9AeRSjpBJX8zs3KEsW55yqfK6XXcRl20l54x8+w0ZPyp1sMD1iL/BJbR/MMBlLaylGGg/QUMsdMM4V6p1futffBxDbqNKvC9BAE24XP/zSskoI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769542250; c=relaxed/simple; bh=Xb+xc8R1aRP1DZaVc1IOpEFUHCEmFeum4D1XaFDWybk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UVEqNyvn0sBbkOluGEVh2/I+u20ujF18xawwRVbofpMTLQkymLY5X09GZJz39na8WKqrxSrVd+Yx7+Wl4rgsDN8JR/f3iy4UxlZ4mBfpK9k9vA9Oujc7OTYl4a8AYpc6u4xDZN3BSXnVi4Vj/p/1Mb++3nIl/D9dUSG0fjCwuMs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UoCRp3/P; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UoCRp3/P" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 748E7C116C6; Tue, 27 Jan 2026 19:30:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769542250; bh=Xb+xc8R1aRP1DZaVc1IOpEFUHCEmFeum4D1XaFDWybk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UoCRp3/PvJtRL9uUKUMuSaU/ZNr6oeqV3RCuFhVjCgZd8x//VhYNUnnt5pcYsGuKT 5qhIL46SNavcTIZ8Jv5URb9fDi6KJcGK9SM+fLlgGQCVyP4ZUEm0hHP0yEw1xcLLRi FcQrnaLlXYSfgBnto6Nb3+N/k6lj4BlgUx8X1kyO8nCKkT/KSEvHP0lJrhaxo+VOUL MM5TwAybb4vkrOM3IqIcB1vfW1m4aUzGawv7JLMAGE+mYsZRdB3e5m7zH1ea6x6jcB 116+gB1VNxLP3DssltYW0BK53oQFU3I9kY0f6dGqyZ+NUzMS5G82qArY4QCT5jaT/K G2p6bpe8uuD6Q== From: Mike Rapoport To: linux-mm@kvack.org Cc: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH RFC 10/17] shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops Date: Tue, 27 Jan 2026 21:29:29 +0200 Message-ID: <20260127192936.1250096-11-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260127192936.1250096-1-rppt@kernel.org> References: <20260127192936.1250096-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Mike Rapoport (Microsoft)" 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. Signed-off-by: Mike Rapoport (Microsoft) fixup Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/shmem_fs.h | 14 ---- include/linux/userfaultfd_k.h | 20 +++-- mm/shmem.c | 148 ++++++++++++---------------------- mm/userfaultfd.c | 79 +++++++++--------- 4 files changed, 106 insertions(+), 155 deletions(-) diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index e2069b3179c4..754f17e5b53c 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -223,20 +223,6 @@ static inline pgoff_t shmem_fallocend(struct inode *in= ode, pgoff_t eof) =20 extern bool shmem_charge(struct inode *inode, long pages); =20 -#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 4d8b879eed91..75d5b09f2560 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -97,6 +97,21 @@ struct vm_uffd_ops { */ struct folio *(*alloc_folio)(struct vm_area_struct *vma, unsigned long addr); + /* + * Called during resolution of UFFDIO_COPY request. + * Should lock the folio and add it to VMA's page cache. + * Returns 0 on success, error code on failre. + */ + 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(). + * The folio should be unlocked, but the reference to it should not be + * dropped. + */ + void (*filemap_remove)(struct folio *folio, struct vm_area_struct *vma); }; =20 /* A combined operation mode + behavior flags. */ @@ -130,11 +145,6 @@ static inline uffd_flags_t uffd_flags_set_mode(uffd_fl= ags_t flags, enum mfill_at /* Flags controlling behavior. These behavior changes are mode-independent= . */ #define MFILL_ATOMIC_WP MFILL_ATOMIC_FLAG(0) =20 -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 lon= g dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags); diff --git a/mm/shmem.c b/mm/shmem.c index 87cd8d2fdb97..6f0485f76cb8 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3169,118 +3169,73 @@ static inline struct inode *shmem_get_inode(struct= mnt_idmap *idmap, #endif /* CONFIG_TMPFS_QUOTA */ =20 #ifdef CONFIG_USERFAULTFD -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) -{ - struct inode *inode =3D file_inode(dst_vma->vm_file); - struct shmem_inode_info *info =3D SHMEM_I(inode); +static struct folio *shmem_mfill_folio_alloc(struct vm_area_struct *vma, + unsigned long addr) +{ + struct inode *inode =3D file_inode(vma->vm_file); struct address_space *mapping =3D inode->i_mapping; + struct shmem_inode_info *info =3D SHMEM_I(inode); + pgoff_t pgoff =3D linear_page_index(vma, addr); gfp_t gfp =3D mapping_gfp_mask(mapping); - pgoff_t pgoff =3D linear_page_index(dst_vma, dst_addr); - void *page_kaddr; struct folio *folio; - int ret; - pgoff_t max_off; - - if (shmem_inode_acct_blocks(inode, 1)) { - /* - * We may have got a page, returned -ENOENT triggering a retry, - * and now we find ourselves with -ENOMEM. Release the page, to - * avoid a BUG_ON in our caller. - */ - if (unlikely(*foliop)) { - folio_put(*foliop); - *foliop =3D NULL; - } - return -ENOMEM; - } =20 - if (!*foliop) { - ret =3D -ENOMEM; - folio =3D shmem_alloc_folio(gfp, 0, info, pgoff); - if (!folio) - goto out_unacct_blocks; + if (unlikely(pgoff >=3D DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE))) + return NULL; =20 - if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) { - page_kaddr =3D kmap_local_folio(folio, 0); - /* - * The read mmap_lock is held here. Despite the - * mmap_lock being read recursive a deadlock is still - * possible if a writer has taken a lock. For example: - * - * process A thread 1 takes read lock on own mmap_lock - * process A thread 2 calls mmap, blocks taking write lock - * process B thread 1 takes page fault, read lock on own mmap lock - * process B thread 2 calls mmap, blocks taking write lock - * process A thread 1 blocks taking read lock on process B - * process B thread 1 blocks taking read lock on process A - * - * Disable page faults to prevent potential deadlock - * and retry the copy outside the mmap_lock. - */ - pagefault_disable(); - ret =3D copy_from_user(page_kaddr, - (const void __user *)src_addr, - PAGE_SIZE); - pagefault_enable(); - kunmap_local(page_kaddr); - - /* fallback to copy_from_user outside mmap_lock */ - if (unlikely(ret)) { - *foliop =3D folio; - ret =3D -ENOENT; - /* don't free the page */ - goto out_unacct_blocks; - } + folio =3D shmem_alloc_folio(gfp, 0, info, pgoff); + if (!folio) + return NULL; =20 - flush_dcache_folio(folio); - } else { /* ZEROPAGE */ - clear_user_highpage(&folio->page, dst_addr); - } - } else { - folio =3D *foliop; - VM_BUG_ON_FOLIO(folio_test_large(folio), folio); - *foliop =3D NULL; + if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) { + folio_put(folio); + return NULL; } =20 - VM_BUG_ON(folio_test_locked(folio)); - VM_BUG_ON(folio_test_swapbacked(folio)); + return folio; +} + +static int shmem_mfill_filemap_add(struct folio *folio, + struct vm_area_struct *vma, + unsigned long addr) +{ + struct inode *inode =3D file_inode(vma->vm_file); + struct address_space *mapping =3D inode->i_mapping; + pgoff_t pgoff =3D linear_page_index(vma, addr); + gfp_t gfp =3D mapping_gfp_mask(mapping); + int err; + __folio_set_locked(folio); __folio_set_swapbacked(folio); - __folio_mark_uptodate(folio); - - ret =3D -EFAULT; - max_off =3D DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); - if (unlikely(pgoff >=3D max_off)) - goto out_release; =20 - ret =3D mem_cgroup_charge(folio, dst_vma->vm_mm, gfp); - if (ret) - goto out_release; - ret =3D shmem_add_to_page_cache(folio, mapping, pgoff, NULL, gfp); - if (ret) - goto out_release; + err =3D shmem_add_to_page_cache(folio, mapping, pgoff, NULL, gfp); + if (err) + goto err_unlock; =20 - ret =3D mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, - &folio->page, true, flags); - if (ret) - goto out_delete_from_cache; + if (shmem_inode_acct_blocks(inode, 1)) { + err =3D -ENOMEM; + goto err_delete_from_cache; + } =20 + folio_add_lru(folio); shmem_recalc_inode(inode, 1, 0); - folio_unlock(folio); + return 0; -out_delete_from_cache: + +err_delete_from_cache: filemap_remove_folio(folio); -out_release: +err_unlock: + folio_unlock(folio); + return err; +} + +static void shmem_mfill_filemap_remove(struct folio *folio, + struct vm_area_struct *vma) +{ + struct inode *inode =3D file_inode(vma->vm_file); + + filemap_remove_folio(folio); + shmem_recalc_inode(inode, 0, 0); folio_unlock(folio); - folio_put(folio); -out_unacct_blocks: - shmem_inode_unacct_blocks(inode, 1); - return ret; } #endif /* CONFIG_USERFAULTFD */ =20 @@ -5317,6 +5272,9 @@ static bool shmem_can_userfault(struct vm_area_struct= *vma, vm_flags_t vm_flags) static const struct vm_uffd_ops shmem_uffd_ops =3D { .can_userfault =3D shmem_can_userfault, .get_folio_noalloc =3D shmem_get_folio_noalloc, + .alloc_folio =3D shmem_mfill_folio_alloc, + .filemap_add =3D shmem_mfill_filemap_add, + .filemap_remove =3D shmem_mfill_filemap_remove, }; #endif =20 diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index b3c12630769c..54aa195237ba 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -14,7 +14,6 @@ #include #include #include -#include #include #include #include "internal.h" @@ -337,10 +336,10 @@ static bool mfill_file_over_size(struct vm_area_struc= t *dst_vma, * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both s= hmem * and anon, and for both shared and private VMAs. */ -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) +static int mfill_atomic_install_pte(pmd_t *dst_pmd, + struct vm_area_struct *dst_vma, + unsigned long dst_addr, struct page *page, + uffd_flags_t flags) { int ret; struct mm_struct *dst_mm =3D dst_vma->vm_mm; @@ -384,9 +383,6 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, goto out_unlock; =20 if (page_in_cache) { - /* Usually, cache pages are already added to LRU */ - if (newly_allocated) - folio_add_lru(folio); folio_add_file_rmap_pte(folio, page, dst_vma); } else { folio_add_new_anon_rmap(folio, dst_vma, dst_addr, RMAP_EXCLUSIVE); @@ -401,6 +397,9 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, =20 set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); =20 + if (page_in_cache) + folio_unlock(folio); + /* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret =3D 0; @@ -507,13 +506,22 @@ static int __mfill_atomic_pte(struct mfill_state *sta= te, */ __folio_mark_uptodate(folio); =20 + if (ops->filemap_add) { + ret =3D ops->filemap_add(folio, state->vma, state->dst_addr); + if (ret) + goto err_folio_put; + } + ret =3D mfill_atomic_install_pte(state->pmd, state->vma, dst_addr, - &folio->page, true, flags); + &folio->page, flags); if (ret) - goto err_folio_put; + goto err_filemap_remove; =20 return 0; =20 +err_filemap_remove: + if (ops->filemap_remove) + ops->filemap_remove(folio, state->vma); err_folio_put: folio_put(folio); /* Don't return -ENOENT so that our caller won't retry */ @@ -526,6 +534,18 @@ static int mfill_atomic_pte_copy(struct mfill_state *s= tate) { const struct vm_uffd_ops *ops =3D vma_uffd_ops(state->vma); =20 + /* + * The normal page fault path for a MAP_PRIVATE mapping in a + * file-backed VMA will invoke the fault, fill the hole in the file and + * COW it right away. The result generates plain anonymous memory. + * So when we are asked to fill a hole in a MAP_PRIVATE mapping, we'll + * generate anonymous memory directly without actually filling the + * hole. For the MAP_PRIVATE case the robustness check only happens in + * the pagetable (to verify it's still none) and not in the page cache. + */ + if (!(state->vma->vm_flags & VM_SHARED)) + ops =3D &anon_uffd_ops; + return __mfill_atomic_pte(state, ops); } =20 @@ -545,7 +565,8 @@ static int mfill_atomic_pte_zeropage(struct mfill_state= *state) spinlock_t *ptl; int ret; =20 - if (mm_forbids_zeropage(dst_vma->vm_mm)) + if (mm_forbids_zeropage(dst_vma->vm_mm) || + (dst_vma->vm_flags & VM_SHARED)) return mfill_atomic_pte_zeroed_folio(state); =20 _dst_pte =3D pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr), @@ -600,11 +621,10 @@ static int mfill_atomic_pte_continue(struct mfill_sta= te *state) } =20 ret =3D mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, - page, false, flags); + page, flags); if (ret) goto out_release; =20 - folio_unlock(folio); return 0; =20 out_release: @@ -827,41 +847,18 @@ extern ssize_t mfill_atomic_hugetlb(struct userfaultf= d_ctx *ctx, =20 static __always_inline ssize_t mfill_atomic_pte(struct mfill_state *state) { - struct vm_area_struct *dst_vma =3D state->vma; - unsigned long src_addr =3D state->src_addr; - unsigned long dst_addr =3D state->dst_addr; - struct folio **foliop =3D &state->folio; uffd_flags_t flags =3D state->flags; - pmd_t *dst_pmd =3D state->pmd; - ssize_t err; =20 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) return mfill_atomic_pte_continue(state); if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) return mfill_atomic_pte_poison(state); + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) + return mfill_atomic_pte_copy(state); + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) + return mfill_atomic_pte_zeropage(state); =20 - /* - * The normal page fault path for a shmem will invoke the - * fault, fill the hole in the file and COW it right away. The - * result generates plain anonymous memory. So when we are - * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll - * generate anonymous memory directly without actually filling - * the hole. For the MAP_PRIVATE case the robustness check - * only happens in the pagetable (to verify it's still none) - * and not in the radix tree. - */ - if (!(dst_vma->vm_flags & VM_SHARED)) { - if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) - err =3D mfill_atomic_pte_copy(state); - else - err =3D mfill_atomic_pte_zeropage(state); - } else { - err =3D shmem_mfill_atomic_pte(dst_pmd, dst_vma, - dst_addr, src_addr, - flags, foliop); - } - - return err; + return -EOPNOTSUPP; } =20 static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, --=20 2.51.0