From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B26C4FCC046 for ; Fri, 6 Mar 2026 17:19:13 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 27FA46B00B2; Fri, 6 Mar 2026 12:19:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2615F6B00B4; Fri, 6 Mar 2026 12:19:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 156B46B00B5; Fri, 6 Mar 2026 12:19:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 01F6C6B00B2 for ; Fri, 6 Mar 2026 12:19:12 -0500 (EST) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id B94D61C76A for ; Fri, 6 Mar 2026 17:19:12 +0000 (UTC) X-FDA: 84516298944.01.47664FF Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf18.hostedemail.com (Postfix) with ESMTP id 346731C0014 for ; Fri, 6 Mar 2026 17:19:10 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="cC/nwaq8"; spf=pass (imf18.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772817551; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=PHNRmaeFkq7BdczmEdv/hsmSWLoNtmEs8tbnt7S4dis=; b=Jm27T9qj8db8zl42OaOzmLHl2ICP7Rs7bpFV3YjLa8iQbCACsOJBsF/ewI4k6U21gwlFUv vMuSoj2sNSfpb8ErX2IXm8Kq5gFikazoabMqoy93ZzXQ4yGY/dTH2u4yItix6Ebm+HQ7B0 c2hYVdGtEeQY8deWqlyAxfI7tIRJT/Q= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="cC/nwaq8"; spf=pass (imf18.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772817551; a=rsa-sha256; cv=none; b=GH+NXtsNj+Be8FvBCj1dLMuzBfqkNvvOZCZHfzk+yuCDh+mObXhYe0rBxAafYdcpIj3ipr AZw3SNPQmta3cYVSafK1pXr0LsKg+iCjbKwsMczoaWpMXoFR0GUI7FPQhg7T4UhtBlihX9 gsOkO1t8JcvF0C8Hfl15B3wGIGQBLe8= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 6DEEC60132; Fri, 6 Mar 2026 17:19:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19E47C4CEF7; Fri, 6 Mar 2026 17:19:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772817549; bh=Sv4+9KeoC3sTffZxTlVqK+mroHcnok9qkJN7lo9ppOs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cC/nwaq8MfXxeznsUWyMc4//fJyQY6Gy3lmbfX8nvg3tpTSws3+Top8otjCejjNcz +iWsx+MFM9OJXHtYj8yDDe0QsR5GgaNijUE+iH18yL/vd0qlWg0FF7YX9jHBrA75zI ooH8y83jzoFddEdNKA/XO6hzr3o/XxzkGcb1OZA18Pla4pR/Ylv+jxmLxEudTXNt51 J6t1gnpJLyayOzNYMTy7o21c7x2lFPQRgWKLocKom/dMGuiHYhOjKAVLJDJ3RRJfuq UOpxQs8qxizckrtpQY357vjvIl+aolRQ/CqSA0cSlaRNQ/UK+XYVR85D3sIBvnb5XH S2TL/AJF5gjCw== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , "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 v2 07/15] userfaultfd: introduce vm_uffd_ops Date: Fri, 6 Mar 2026 19:18:07 +0200 Message-ID: <20260306171815.3160826-8-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260306171815.3160826-1-rppt@kernel.org> References: <20260306171815.3160826-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 346731C0014 X-Rspamd-Server: rspam08 X-Stat-Signature: 8oyhu56naajtdh5mfakocj1zs7enoqec X-HE-Tag: 1772817550-726935 X-HE-Meta: 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 YRHuzuCH cAGoLxssYFYNwt5HWszLSoSrcRVKBggzb6eQRcMmEHrSYAF0Lf5RmXAdst//6T6JAYfEcLyocI8HeAZrWbeL/Ybl1ueqEvSLsniHDaPGiYeT3kCpmYyF3Fh8FOabDSplEiqLwgepWaxEfJenWybCjEYdN3dIW7M5U+VU6ruLW686yN+dNllmPZSX5VRyj+awGmmBT6kU2UuXPWhcRQ8isAsmXvrv5rQ8WvpBvkMASFFIsoO0bJjWNOav5/azEviP7dWglpC/zm0sRdNuwKCQuu2xvN1uL9ADUjSMb Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 | 36 ++++++++++++++++++++++++++--------- 5 files changed, 68 insertions(+), 9 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 5be3d8a8f806..b63b28c65676 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -741,6 +741,8 @@ struct vm_fault { */ }; +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 }; #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 { extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason); +/* 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; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 0beb6e22bc26..077968a8a69a 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4818,6 +4818,18 @@ static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf) return 0; } +#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 = { + .can_userfault = 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 = { .close = hugetlb_vm_op_close, .may_split = hugetlb_vm_op_split, .pagesize = hugetlb_vm_op_pagesize, +#ifdef CONFIG_USERFAULTFD + .uffd_ops = &hugetlb_uffd_ops, +#endif }; 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 = { + .can_userfault = shmem_can_userfault, +}; #endif /* CONFIG_USERFAULTFD */ #ifdef CONFIG_TMPFS @@ -5313,6 +5322,9 @@ static const struct vm_operations_struct shmem_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .uffd_ops = &shmem_uffd_ops, +#endif }; static const struct vm_operations_struct shmem_anon_vm_ops = { @@ -5322,6 +5334,9 @@ static const struct vm_operations_struct shmem_anon_vm_ops = { .set_policy = shmem_set_policy, .get_policy = shmem_get_policy, #endif +#ifdef CONFIG_USERFAULTFD + .uffd_ops = &shmem_uffd_ops, +#endif }; int shmem_init_fs_context(struct fs_context *fc) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index c5fd1e5c67b3..b55d4a8d88cc 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -34,6 +34,25 @@ struct mfill_state { pmd_t *pmd; }; +static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags) +{ + /* 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 = { + .can_userfault = 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_end) { @@ -2023,13 +2042,15 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, bool wp_async) { - vm_flags &= __VM_UFFD_FLAGS; + const struct vm_uffd_ops *ops = vma_uffd_ops(vma); - if (vma->vm_flags & VM_DROPPABLE) + /* only VMAs that implement vm_uffd_ops are supported */ + if (!ops) return false; - if ((vm_flags & VM_UFFD_MINOR) && - (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma))) + vm_flags &= __VM_UFFD_FLAGS; + + if (vma->vm_flags & VM_DROPPABLE) return false; /* @@ -2041,16 +2062,13 @@ bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, /* * 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; - /* 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); } static void userfaultfd_set_vm_flags(struct vm_area_struct *vma, -- 2.51.0