From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 CBFBC324716 for ; Fri, 22 May 2026 16:00:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779465620; cv=none; b=tPTRosKw8hlrqubnCB2AQWpUr5pSmKKo2MdlogrsLv9a7lS/dOh5z2/D7E9v3JKzJR3ihLIYbv23zKQnLgJfrs6ZRz2Y6t2r+9u8BXl4vdEPmAzRtRvtB8LLBAQrL4Tp5/5WeDTWETKciELfIlKy8svjpxkT8pWYrz1pvM5UrGM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779465620; c=relaxed/simple; bh=gjTLxm0IhdUF+Cu6h4zY+Rk7QBKewHR4TjsBWZGAj8E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=sisAXF/kMHdv5F0icQGb4rFnZKODxdzxxVt0uaJga6lVzCb2buyQRICPchP23eBjv8UgI/UhRHLHgotEPjowpZB/8AEf7YcT2OtwDf3VXVd0cFxXtl3B6AkvRJjsgtB+LxP8MRtg42ln2tm8IGC9HT+lmsU3IjWZkwjzPi6aif4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RHdFvXgs; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RHdFvXgs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B653B1F000E9; Fri, 22 May 2026 16:00:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779465618; bh=8LOOvoPFc1mo7/HC1v7nzO3pf/LAnx00Q0CZDsLJWW4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=RHdFvXgsYN95BR9977HUHQQgTuhBtlxR8o+rQH02po4VcJ//Nh2tmhcBYlkvtVX9s kCULTY/FXdP2cjhP32hzVQG14Wxqy/JHiidi7bkTVckgN8VxTVXaN2pO/3GexjKY4O 9qz1T10MsuxxuMX6XEo0IwzY0TJbbg7GebhVqPD06vp0d0aql20oAETS5HY02gs09t 2mavmvbFhp+AW5ZpGCIz9uDOPS3a+aDeCN6bjOJWX6km0Z3BEZsBOFwig0W8GrX4xp WNv9HnqiUKRFuWiCeS3L+2Zavc2v9xE9xw8fnTIlff6X6FmJNcDBTpMn5wlQWgRZzR o7gjjUl998aAg== From: Lorenzo Stoakes To: Andrew Morton Cc: Arnd Bergmann , Greg Kroah-Hartman , David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 1/3] drivers/char/mem: eliminate unnecessary use of success_hook Date: Fri, 22 May 2026 17:00:09 +0100 Message-ID: <5d1e8bd29d6e070218ba7a03461df562e372b91e.1779462249.git.ljs@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit /dev/zero, uniquely, marks memory mapped there as anonymous. This is currently achieved using the mmap_action->success_hook. However this hook circumvents the abstraction of VMA initialisation so it's preferable to do things a different way. To achieve this, this patch firstly defaults the VMA descriptor's vm_ops field to the dummy VMA operations, which is what file-backed VMAs default this field to. That way, we can detect whether a driver sets this field to NULL in order to mark it anonymous. We then introduce vma_desc_set_anonymous() to do this explicitly, and invoke it in mmap_zero_prepare(). This way, any driver which does not explicitly set desc->vm_ops, retains the dummy vm_ops as they would previously. We also update set_vma_user_defined_fields() to make clear that we are either setting vma->vm_ops to what is provided by the driver (or defaulting to dummy_vm_ops if not set), or setting the VMA anonymous. This lays the groundwork for removing the success hook. Signed-off-by: Lorenzo Stoakes --- drivers/char/mem.c | 17 +++++------------ include/linux/mm.h | 5 +++++ mm/util.c | 1 + mm/vma.c | 3 +++ tools/testing/vma/include/dup.h | 1 + 5 files changed, 15 insertions(+), 12 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 5fd421e48c04..a4297eb39887 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -504,17 +504,6 @@ static ssize_t read_zero(struct file *file, char __user *buf, return cleared; } -static int mmap_zero_private_success(const struct vm_area_struct *vma) -{ - /* - * This is a highly unique situation where we mark a MAP_PRIVATE mapping - * of /dev/zero anonymous, despite it not being. - */ - vma_set_anonymous((struct vm_area_struct *)vma); - - return 0; -} - static int mmap_zero_prepare(struct vm_area_desc *desc) { #ifndef CONFIG_MMU @@ -523,7 +512,11 @@ static int mmap_zero_prepare(struct vm_area_desc *desc) if (vma_desc_test(desc, VMA_SHARED_BIT)) return shmem_zero_setup_desc(desc); - desc->action.success_hook = mmap_zero_private_success; + /* + * This is a highly unique situation where we mark a MAP_PRIVATE mapping + * of /dev/zero anonymous, despite it not being. + */ + vma_desc_set_anonymous(desc); return 0; } diff --git a/include/linux/mm.h b/include/linux/mm.h index 9cedc5e75aa9..2138c86403f5 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1489,6 +1489,11 @@ static inline void vma_set_anonymous(struct vm_area_struct *vma) vma->vm_ops = NULL; } +static inline void vma_desc_set_anonymous(struct vm_area_desc *desc) +{ + desc->vm_ops = NULL; +} + static inline bool vma_is_anonymous(struct vm_area_struct *vma) { return !vma->vm_ops; diff --git a/mm/util.c b/mm/util.c index 3cc949a0b7ed..2b2a9df689d7 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1192,6 +1192,7 @@ void compat_set_desc_from_vma(struct vm_area_desc *desc, desc->vm_file = vma->vm_file; desc->vma_flags = vma->flags; desc->page_prot = vma->vm_page_prot; + desc->vm_ops = vma->vm_ops; /* Default. */ desc->action.type = MMAP_NOTHING; diff --git a/mm/vma.c b/mm/vma.c index d90791b00a7b..9eea2850818a 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2697,6 +2697,8 @@ static void set_vma_user_defined_fields(struct vm_area_struct *vma, { if (map->vm_ops) vma->vm_ops = map->vm_ops; + else /* Only /dev/zero should do this. */ + vma_set_anonymous(vma); vma->vm_private_data = map->vm_private_data; } @@ -2744,6 +2746,7 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr, .action = { .type = MMAP_NOTHING, /* Default to no further action. */ }, + .vm_ops = &vma_dummy_vm_ops, }; bool allocated_new = false; int error; diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 9e0dfd3a85b0..306171d061e7 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -1303,6 +1303,7 @@ static inline void compat_set_desc_from_vma(struct vm_area_desc *desc, desc->vm_file = vma->vm_file; desc->vma_flags = vma->flags; desc->page_prot = vma->vm_page_prot; + desc->vm_ops = vma->vm_ops; /* Default. */ desc->action.type = MMAP_NOTHING; -- 2.54.0