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 39AB230EF90 for ; Fri, 22 May 2026 16:00:23 +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=1779465625; cv=none; b=iuYTKDdRy2GVDSxLO5Wtu/pmB3/2vLgdKQRyHTYC67bURuy2eDMy5h4iqcomeuDroxAJps6khWoPD/K0M+op8hSNIBGteYWf+zo6QsAy65+ZX7wMU1EGouicigCJqXnOTKgTENydESVFADbkeEomEf2kGoW0Ehb27WRpBgUdoWQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779465625; c=relaxed/simple; bh=0MeNjHSMwHnl43ZnJr7lANquz7kQAjnacczqJ72j1rA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=P+8U4fVrGIJjLTh67cGFE9qu9nqSqX9QkP7uouU8DyfEOIhjOroQlbJb48enZ2MVMy2rha8A5F3144F2O0aP5/Gzcs12sn0F9vWNt4Cm1KLpXysufC5MmGnQFGHh2cuhQ/wip6HLQ1+aek19Fm2rr7yx3v4EMtzZ/7DvVWsoEqY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aHQW+4zp; 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="aHQW+4zp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4249D1F00A3D; Fri, 22 May 2026 16:00:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779465623; bh=316RJj3nC9oY2FUmt7SPv6BDYnUsOE3VTbuP2TV/Ess=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=aHQW+4zp4Ue8xoxOd05U7Jt/Y2i2slzBpf2CQ1ORoAad8i7w9ZQU29LvdVg7Mt4ym HlN43tUOzQxvRhXfBTuhVKnY6kMoZgR36LpiKoNT+Sc2MTFHQuUVm4wfoB7J7zAdKr 9wNTfKvz0gnfcKwuqecKaDhLKnq96mZS1xb/JJhCGECEcTTYnWjcEipnLd7jsC7ldz mhgsA+1oQI7sZnGQndk/YjfGgr1sKZ8/CHfnfaPFqgoteq55Udg1YtJjWQ0wuVNLMz myMa97/dN7g/i1JFfq35hneSFMuZnoDSuRSrEWkRRcS6bfNlEjdIvqN97fN52YtVtJ RWRDJAO4QQmPA== 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 3/3] mm/vma: eliminate mmap_action->error_hook, introduce error_filter Date: Fri, 22 May 2026 17:00:11 +0100 Message-ID: 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 Rather than providing a hook, simplify things by providing the ability to filter errors. This allows us to more carefully validate the value provided and thus ensure only a valid error code is specified, and simplifies the interface. This way, we eliminate all hooks but mmap_prepare and allow only mmap actions to be specified (which core mm controls). This significantly improves robustness and eliminates any unnecessary code duplication in driver mmap hooks. We also update the /dev/mem logic (the only user) to use mmap_action->error_filter instead. Signed-off-by: Lorenzo Stoakes --- drivers/char/mem.c | 8 +------- include/linux/mm_types.h | 9 +++------ mm/util.c | 29 +++++++++++++++++++++-------- tools/testing/vma/include/dup.h | 9 +++------ 4 files changed, 28 insertions(+), 27 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index a4297eb39887..11639d988e47 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -322,11 +322,6 @@ static const struct vm_operations_struct mmap_mem_ops = { #endif }; -static int mmap_filter_error(int err) -{ - return -EAGAIN; -} - static int mmap_mem_prepare(struct vm_area_desc *desc) { struct file *file = desc->file; @@ -362,8 +357,7 @@ static int mmap_mem_prepare(struct vm_area_desc *desc) /* Remap-pfn-range will mark the range with the I/O flag. */ mmap_action_remap_full(desc, desc->pgoff); - /* We filter remap errors to -EAGAIN. */ - desc->action.error_hook = mmap_filter_error; + desc->action.error_filter = -EAGAIN; return 0; } diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 945c0a5386d6..8d1fb85e7684 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -844,13 +844,10 @@ struct mmap_action { enum mmap_action_type type; /* - * If specified, this hook is invoked when an error occurred when - * attempting the selected action. - * - * The hook can return an error code in order to filter the error, but - * it is not valid to clear the error here. + * If non-zero, filter errors that arise from mmap actions such that we + * return error_filter instead. Only valid error codes may be specified. */ - int (*error_hook)(int err); + int error_filter; /* * This should be set in rare instances where the operation required diff --git a/mm/util.c b/mm/util.c index 4e172990afcd..9b4e5432d45a 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1414,16 +1414,22 @@ static int mmap_action_finish(struct vm_area_struct *vma, */ len = vma_pages(vma) << PAGE_SHIFT; do_munmap(current->mm, vma->vm_start, len, NULL); - if (action->error_hook) { - /* We may want to filter the error. */ - err = action->error_hook(err); - /* The caller should not clear the error. */ - VM_WARN_ON_ONCE(!err); - } - return err; + + return action->error_filter ?: err; } #ifdef CONFIG_MMU + +static int check_mmap_action(struct mmap_action *action) +{ + const unsigned long filter = action->error_filter; + + if (WARN_ON_ONCE(filter && !IS_ERR_VALUE(filter))) + return -EINVAL; + + return 0; +} + /** * mmap_action_prepare - Perform preparatory setup for an VMA descriptor * action which need to be performed. @@ -1433,7 +1439,14 @@ static int mmap_action_finish(struct vm_area_struct *vma, */ int mmap_action_prepare(struct vm_area_desc *desc) { - switch (desc->action.type) { + struct mmap_action *action = &desc->action; + int err; + + err = check_mmap_action(action); + if (err) + return err; + + switch (action->type) { case MMAP_NOTHING: return 0; case MMAP_REMAP_PFN: diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index fddfd1b57c09..bcd569a72087 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -483,13 +483,10 @@ struct mmap_action { enum mmap_action_type type; /* - * If specified, this hook is invoked when an error occurred when - * attempting the selection action. - * - * The hook can return an error code in order to filter the error, but - * it is not valid to clear the error here. + * If non-zero, filter errors that arise from mmap actions such that we + * return error_filter instead. Only valid error codes may be specified. */ - int (*error_hook)(int err); + int error_filter; /* * This should be set in rare instances where the operation required -- 2.54.0