From nobody Sat Apr 4 03:19:49 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 89AF535F193; Thu, 2 Apr 2026 04:12:54 +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=1775103174; cv=none; b=Lrd0bzCls7bG9Uo2SkKSEy58yd9kof2BhvSQh+JDZY8k+zN0VddIFN8pBZMCFXW3ZUmmuq4ZsT+zY6/dBEq5MFLWzuHVtmvXy0ugUUX+fPMAAt0OxryL0GAXk148FKvvgxOmjvEFqc64ww/cm/+or0dTMSmrIojH4eoIru7TQ04= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775103174; c=relaxed/simple; bh=u+ZOOG8J/28GYuaj/GsT8WwOacoYSYHh4DClfNVux6U=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lDOQJ+QLEEi/EuW+tKI4pXkG6/D17MmYgvYApeS0veZf2hbZPFETgTDyYFREqJwTT/UCgKBth5hiiUTravpLXtIDxl74kYQrRM2glnV4MjVIKY34VRWML2aj6jTTOfySS6FiGaEDCijF3itdVWa2oeHAGb1Odtj5nXp0vj8qigA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TdSj8YsX; 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="TdSj8YsX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECC46C19424; Thu, 2 Apr 2026 04:12:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775103174; bh=u+ZOOG8J/28GYuaj/GsT8WwOacoYSYHh4DClfNVux6U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TdSj8YsXBms6JMAXx3iKSbSOLf55gYfGk7tRtNBmt2PPcCj1b72nOaSt/Gln8t2zP XjsJg346ucFFyRRuzQXzhxyks7T2lEdZ7ogc9gnOrdgaQ5QjP8V0VvOE9a5FBTY1Cw ORQqpoFHeKJ23FSOWzoATxDQaoQVb96FHm3eknirxT8Fkankpbs2lQ3wLr09EAukiX WXPsaCuhxUxonyH+iV5G/7Yob6GwVhzWX+FTATjT4GetWJyJYxwYXy5IDebYViHGgV Frk9QL5Uw5aOkd8BWjWdkNmuioCwS42Tt98HOL740axM7BFjNYNo/28E+iFJoKYRCz ppKu1Rx0OwaRQ== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Andrei Vagin , Axel Rasmussen , Baolin Wang , David Hildenbrand , Harry Yoo , Hugh Dickins , James Houghton , "Liam R. Howlett" , "Lorenzo Stoakes (Oracle)" , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v4 07/15] userfaultfd: introduce vm_uffd_ops Date: Thu, 2 Apr 2026 07:11:48 +0300 Message-ID: <20260402041156.1377214-8-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260402041156.1377214-1-rppt@kernel.org> References: <20260402041156.1377214-1-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)" Current userfaultfd implementation works only with memory managed by core MM: anonymous, shmem and hugetlb. First, there is no fundamental reason to limit userfaultfd support only to the core memory types and userfaults can be handled similarly to regular page faults provided a VMA owner implements appropriate callbacks. Second, historically various code paths were conditioned on vma_is_anonymous(), vma_is_shmem() and is_vm_hugetlb_page() and some of these conditions can be expressed as operations implemented by a particular memory type. Introduce vm_uffd_ops extension to vm_operations_struct that will delegate memory type specific operations to a VMA owner. Operations for anonymous memory are handled internally in userfaultfd using anon_uffd_ops that implicitly assigned to anonymous VMAs. Start with a single operation, ->can_userfault() that will verify that a VMA meets requirements for userfaultfd support at registration time. Implement that method for anonymous, shmem and hugetlb and move relevant parts of vma_can_userfault() into the new callbacks. Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm.h | 5 ++++ include/linux/userfaultfd_k.h | 6 +++++ mm/hugetlb.c | 15 ++++++++++++ mm/shmem.c | 15 ++++++++++++ mm/userfaultfd.c | 44 ++++++++++++++++++++++++----------- 5 files changed, 72 insertions(+), 13 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index abb4963c1f06..0fbeb8012983 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -741,6 +741,8 @@ struct vm_fault { */ }; =20 +struct vm_uffd_ops; + /* * These are the virtual MM functions - opening of an area, closing and * unmapping it (needed to keep files on disk up-to-date etc), pointer @@ -826,6 +828,9 @@ 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 + const struct vm_uffd_ops *uffd_ops; +#endif }; =20 #ifdef CONFIG_NUMA_BALANCING diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index a49cf750e803..56e85ab166c7 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -80,6 +80,12 @@ struct userfaultfd_ctx { =20 extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long rea= son); =20 +/* VMA userfaultfd operations */ +struct vm_uffd_ops { + /* Checks if a VMA can support userfaultfd */ + bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags); +}; + /* A combined operation mode + behavior flags. */ typedef unsigned int __bitwise uffd_flags_t; =20 diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 327eaa4074d3..530bc4337be6 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4818,6 +4818,18 @@ static vm_fault_t hugetlb_vm_op_fault(struct vm_faul= t *vmf) return 0; } =20 +#ifdef CONFIG_USERFAULTFD +static bool hugetlb_can_userfault(struct vm_area_struct *vma, + vm_flags_t vm_flags) +{ + return true; +} + +static const struct vm_uffd_ops hugetlb_uffd_ops =3D { + .can_userfault =3D hugetlb_can_userfault, +}; +#endif + /* * When a new function is introduced to vm_operations_struct and added * to hugetlb_vm_ops, please consider adding the function to shm_vm_ops. @@ -4831,6 +4843,9 @@ const struct vm_operations_struct hugetlb_vm_ops =3D { .close =3D hugetlb_vm_op_close, .may_split =3D hugetlb_vm_op_split, .pagesize =3D hugetlb_vm_op_pagesize, +#ifdef CONFIG_USERFAULTFD + .uffd_ops =3D &hugetlb_uffd_ops, +#endif }; =20 static pte_t make_huge_pte(struct vm_area_struct *vma, struct folio *folio, diff --git a/mm/shmem.c b/mm/shmem.c index b40f3cd48961..f2a25805b9bf 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3294,6 +3294,15 @@ int shmem_mfill_atomic_pte(pmd_t *dst_pmd, shmem_inode_unacct_blocks(inode, 1); return ret; } + +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 =3D { + .can_userfault =3D shmem_can_userfault, +}; #endif /* CONFIG_USERFAULTFD */ =20 #ifdef CONFIG_TMPFS @@ -5313,6 +5322,9 @@ 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 + .uffd_ops =3D &shmem_uffd_ops, +#endif }; =20 static const struct vm_operations_struct shmem_anon_vm_ops =3D { @@ -5322,6 +5334,9 @@ 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 + .uffd_ops =3D &shmem_uffd_ops, +#endif }; =20 int shmem_init_fs_context(struct fs_context *fc) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index d51e080e9216..e3024a39c19d 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -34,6 +34,25 @@ struct mfill_state { pmd_t *pmd; }; =20 +static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_f= lags) +{ + /* anonymous memory does not support MINOR mode */ + if (vm_flags & VM_UFFD_MINOR) + return false; + return true; +} + +static const struct vm_uffd_ops anon_uffd_ops =3D { + .can_userfault =3D anon_can_userfault, +}; + +static const struct vm_uffd_ops *vma_uffd_ops(struct vm_area_struct *vma) +{ + if (vma_is_anonymous(vma)) + return &anon_uffd_ops; + return vma->vm_ops ? vma->vm_ops->uffd_ops : NULL; +} + static __always_inline bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_en= d) { @@ -2021,34 +2040,33 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, uns= igned long dst_start, bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, bool wp_async) { - vm_flags &=3D __VM_UFFD_FLAGS; + const struct vm_uffd_ops *ops =3D vma_uffd_ops(vma); =20 - if (vma->vm_flags & VM_DROPPABLE) - return false; - - if ((vm_flags & VM_UFFD_MINOR) && - (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma))) - return false; + vm_flags &=3D __VM_UFFD_FLAGS; =20 /* - * If wp async enabled, and WP is the only mode enabled, allow any + * If WP is the only mode enabled and context is wp async, allow any * memory type. */ if (wp_async && (vm_flags =3D=3D VM_UFFD_WP)) return true; =20 + /* For any other mode reject VMAs that don't implement vm_uffd_ops */ + if (!ops) + return false; + + if (vma->vm_flags & VM_DROPPABLE) + return false; + /* * If user requested uffd-wp but not enabled pte markers for - * uffd-wp, then shmem & hugetlbfs are not supported but only - * anonymous. + * uffd-wp, then only anonymous memory is supported */ if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) && !vma_is_anonymous(vma)) return false; =20 - /* By default, allow any of anon|shmem|hugetlb */ - return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) || - vma_is_shmem(vma); + return ops->can_userfault(vma, vm_flags); } =20 static void userfaultfd_set_vm_flags(struct vm_area_struct *vma, --=20 2.53.0