From nobody Mon Dec 1 22:36:21 2025 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 5EF9D27A10F; Sun, 30 Nov 2025 11:18:33 +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=1764501513; cv=none; b=AjWXmjILljlBFQZaCp4/XAZOuB2+z57/LGzWOOIEPvzrXs6N/e9USCfTcybTbRw7bQj3wZVjMIMd0OKtGatw7GLb+2pw4ZuXhZKunOLeTQT9GPe4dGBDQELckcHgnN2UmCJepTRwg1XHYXlepiOUNYgZXRBwx5MCpJNj/1VKGGI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764501513; c=relaxed/simple; bh=No4OV/v0jQLoJl8PKO7GG/i2wSSVo7iZmz3MRUSzNrc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ojiMLhQjOAG0Z4lnO/CpzAGEIdjWLGHvg+iLRJVecjeBk9121s3E1DvK8k37GO8WlXklYj3iplZ+JWgM3HNfECgMMrQGMBb9DdKVfw48v+Dm4MjyY/WyaUpLX3uablgwBI6nEvFTHO9ibfu9jB6NlglUMmaTcj0Wx0HB7TSskc4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YeR77mac; 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="YeR77mac" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 353A8C116D0; Sun, 30 Nov 2025 11:18:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764501512; bh=No4OV/v0jQLoJl8PKO7GG/i2wSSVo7iZmz3MRUSzNrc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YeR77mac03xw5SwBGRtzdZ/H+sOjspFJtYv8n6QV1GoUAtA5YBQtzB6KvA1McmoCj KG9n1DxTyB8f5KX+wIv7kufbSzy9gESul7fy+1PQlps2ZbpuCHnm//qNHYAl6rdb0g ppVz3ebKn5ThslvEpG/WIw0IQHAldkujMXFaHsjXgP69Fz5mFFnoaSO+M6Q/scZEFb zXrX8iNB+/84yNGOQcJwEYDy8DWE2tSsHnhfkHwtFBe/HSjUf9gGvwuYyXcHM6oz0c ORCVRYxO9icX1iVxjlcEPlwN8P+xjOcnQy4RUFOe38vEVO47X8Lwl16TMsJn4Sb/KE aPvK0vIq3++yA== 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 , Nikita Kalyazin , 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, "David Hildenbrand (Red Hat)" Subject: [PATCH v3 2/5] userfaultfd, shmem: use a VMA callback to handle UFFDIO_CONTINUE Date: Sun, 30 Nov 2025 13:18:09 +0200 Message-ID: <20251130111812.699259-3-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251130111812.699259-1-rppt@kernel.org> References: <20251130111812.699259-1-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)" 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_operations_struct' 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_atomic() and mfill_atomic_pte_continue() to support this new API. Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Liam R. Howlett Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm.h | 9 ++++++++ mm/shmem.c | 18 ++++++++++++++++ mm/userfaultfd.c | 52 +++++++++++++++++++++++++++++----------------- 3 files changed, 60 insertions(+), 19 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 7c79b3369b82..6351a9cde360 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -690,6 +690,15 @@ struct vm_operations_struct { struct page *(*find_normal_page)(struct vm_area_struct *vma, unsigned long addr); #endif /* CONFIG_FIND_NORMAL_PAGE */ +#ifdef CONFIG_USERFAULTFD + /* + * Called by userfault 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); +#endif }; =20 #ifdef CONFIG_NUMA_BALANCING diff --git a/mm/shmem.c b/mm/shmem.c index 5a3f0f754dc0..9f8c54ad0e32 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3262,6 +3262,18 @@ int shmem_mfill_atomic_pte(pmd_t *dst_pmd, shmem_inode_unacct_blocks(inode, 1); return ret; } + +static struct folio *shmem_get_folio_noalloc(struct inode *inode, pgoff_t = pgoff) +{ + struct folio *folio; + int err; + + err =3D shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + if (err) + return ERR_PTR(err); + + return folio; +} #endif /* CONFIG_USERFAULTFD */ =20 #ifdef CONFIG_TMPFS @@ -5294,6 +5306,9 @@ static const struct vm_operations_struct shmem_vm_ops= =3D { .set_policy =3D shmem_set_policy, .get_policy =3D shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .get_folio_noalloc =3D shmem_get_folio_noalloc, +#endif }; =20 static const struct vm_operations_struct shmem_anon_vm_ops =3D { @@ -5303,6 +5318,9 @@ static const struct vm_operations_struct shmem_anon_v= m_ops =3D { .set_policy =3D shmem_set_policy, .get_policy =3D shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .get_folio_noalloc =3D shmem_get_folio_noalloc, +#endif }; =20 int shmem_init_fs_context(struct fs_context *fc) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 8dc964389b0d..5610f29dac73 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -388,15 +388,12 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, struct page *page; int ret; =20 - ret =3D shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); + folio =3D dst_vma->vm_ops->get_folio_noalloc(inode, pgoff); /* Our caller expects us to return -EFAULT if we failed to find folio */ - if (ret =3D=3D -ENOENT) - ret =3D -EFAULT; - if (ret) - goto out; - if (!folio) { - ret =3D -EFAULT; - goto out; + if (IS_ERR_OR_NULL(folio)) { + if (PTR_ERR(folio) =3D=3D -ENOENT || !folio) + return -EFAULT; + return PTR_ERR(folio); } =20 page =3D folio_file_page(folio, pgoff); @@ -411,13 +408,12 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, goto out_release; =20 folio_unlock(folio); - ret =3D 0; -out: - return ret; + return 0; + out_release: folio_unlock(folio); folio_put(folio); - goto out; + return ret; } =20 /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */ @@ -694,6 +690,15 @@ static __always_inline ssize_t mfill_atomic_pte(pmd_t = *dst_pmd, return err; } =20 +static __always_inline bool vma_can_mfill_atomic(struct vm_area_struct *vm= a, + uffd_flags_t flags) +{ + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) + return vma->vm_ops && vma->vm_ops->get_folio_noalloc; + + return vma_is_anonymous(vma) || vma_is_shmem(vma); +} + static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, @@ -766,10 +771,7 @@ static __always_inline ssize_t mfill_atomic(struct use= rfaultfd_ctx *ctx, return mfill_atomic_hugetlb(ctx, dst_vma, dst_start, src_start, len, flags); =20 - if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) - goto out_unlock; - if (!vma_is_shmem(dst_vma) && - uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) + if (!vma_can_mfill_atomic(dst_vma, flags)) goto out_unlock; =20 while (src_addr < src_start + len) { @@ -1985,9 +1987,21 @@ bool vma_can_userfault(struct vm_area_struct *vma, v= m_flags_t vm_flags, if (vma->vm_flags & VM_DROPPABLE) return false; =20 - if ((vm_flags & VM_UFFD_MINOR) && - (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma))) - return false; + if (vm_flags & VM_UFFD_MINOR) { + /* + * If only MINOR mode is requested and we can request an + * existing folio from VMA's page cache, allow it + */ + if (vm_flags =3D=3D VM_UFFD_MINOR && vma->vm_ops && + vma->vm_ops->get_folio_noalloc) + return true; + /* + * Only hugetlb and shmem can support MINOR mode in combination + * with other modes + */ + if (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma)) + return false; + } =20 /* * If wp async enabled, and WP is the only mode enabled, allow any --=20 2.51.0