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 9D05BCC6B01 for ; Thu, 2 Apr 2026 04:12:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 05ECB6B009E; Thu, 2 Apr 2026 00:12:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 036C26B009F; Thu, 2 Apr 2026 00:12:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EB55C6B00A0; Thu, 2 Apr 2026 00:12:56 -0400 (EDT) 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 DD3136B009E for ; Thu, 2 Apr 2026 00:12:56 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 99697589BA for ; Thu, 2 Apr 2026 04:12:56 +0000 (UTC) X-FDA: 84612295152.27.144F36E Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf13.hostedemail.com (Postfix) with ESMTP id 1C0B220008 for ; Thu, 2 Apr 2026 04:12:54 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=TdSj8YsX; spf=pass (imf13.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=1775103175; 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=Kkfv24X+ztWChD7WQDcL92+RM8gh0RWTpJeeZqBKkIU=; b=US7Ql0kqvYjZ0J63L0J8RcyoQLiuIUnhevBn1WvsdBcAN0bIoGgucBlvfbFk5BmcGw5xKD 7+ixmZIXPw3H1qDAoak5H+rtaEA8SAYIVlarE17ZAVQp0Jov13SSbP/mPuBugSzonEGNG7 lnzoc+UbermY5Ce1CYV6Z8NpLiHedH4= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1775103175; a=rsa-sha256; cv=none; b=nN/Uou3LGRVZtuaNqa9rEmpCDc4m5eCQ7aAvzUnKP/3Be6w1l0lVXiG26prG7gB13HeJF5 pAglZuucuvS+l5/YghtkXfJdyTH7WtY/cUl3nJPOvjAwizmYxV1/ilcAad3jIBD3cX1v0i ap1C23NxC4Hbjz6mXTktk3Ha+itdh1k= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=TdSj8YsX; spf=pass (imf13.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 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 81EC16186C; Thu, 2 Apr 2026 04:12:54 +0000 (UTC) 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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 1C0B220008 X-Stat-Signature: aqssyj8pr8mhathgdp43nyphk73ooeg7 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1775103174-160051 X-HE-Meta: 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 FOcnORj7 ccw5Rh8yy2CMPzWJzhN4mnGPXE9u+Cc/ulPfsF33eRCQswYCUQi/7gMBJng1O7QpEGQK8I39MekHnAYV+C6qjGtg0v9JtyXx2mUOti0KFmZWp9iCPIePDogndL7k9GqGTzx5fXNMdzpzC36YtGAPZ2CZ7ea6uJJ0SAB/Tl0rnkjIQ9aIks6yTnC1sV3XmSlR2Vu6IgLoBb6+RrbR54z85qf2Jf8JOYz+he83NOUPRsvcUBeYxvx8Xa19tO7G0F/BFX+pEvo5Ux0KLi/I4ZB+pMwiYQw== 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 | 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 { */ }; +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 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_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 d51e080e9216..e3024a39c19d 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) { @@ -2021,34 +2040,33 @@ 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) - return false; - - if ((vm_flags & VM_UFFD_MINOR) && - (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma))) - return false; + vm_flags &= __VM_UFFD_FLAGS; /* - * 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 == VM_UFFD_WP)) return true; + /* 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; - /* 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, -- 2.53.0