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 ECF013DBD63 for ; Mon, 1 Jun 2026 15:25:51 +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=1780327560; cv=none; b=egjLOxAYvD4RpIUG0iYLp4KS9HTbZ+RuZbApLuvpt0MxTTdVqOqbQ6oNkXNY9lnaQWZ0FbwSP1xMQf64QoKyXqOgqK8ENUJg8+SFv/I3LBk9797mhoxhyXBt+iUyBt61uvSC6OSYxkU1h/FU4SAxInJJpOzHOgFz2S6TG4eS20w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780327560; c=relaxed/simple; bh=bG7HMChbzz6nygmC5DTnEexwo5ssaWLuXZJVkB2a8eQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rIrdEuRZYQXLBdYP3NIS3C/0l4pAWjZaF4EEBjaVhuGjZlglYVwWlsUjvKLhEQgyl+2aVsYGzpdceSyKM0xmQeurQLufZ5SINxwfcU/ormhG4aQykUc4vmBFzHIo69kRwmnUKYGlkAb44d+xmPenPXaR8QvA66AGo92zCVhNBWM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Evw7um1L; 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="Evw7um1L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6E841F00893; Mon, 1 Jun 2026 15:25:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780327551; bh=5wt1AxhWkdz5vT4IX+aS+7S39jLcDgUB3QRpVfwNb0U=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Evw7um1L70qffU6mAIbK7qY2EAwv6itIIW7jvKm7LzRoN8ezL4Cls8zqSGfGFkaDw NGBS2bv03RJwJw6Hz7zmIpO758fpzurp1JEG/mIBf4AVRyapHhG8QeX7vWsOBNb1yt Sw1LRIzzn6KdAXWwug/OdfFMjcyn3cc0wTGAhDzIWyAaORBpGgZ6KLHVGCa/5kuj2e M1fzD+mw2heTkG6gCKTMj3ZlFxXSID+loWxeGaWXUwZI0RhtFn3ZUY+dSd55tP+tZI TtVnrplbUyLwlMKGqfGQD7g79zVTQpR1PdoHdXvDubNUR9kAB74ViLv5Q/iLG5MoTt bTRFlb7e3JDBQ== Message-ID: <88aa89e7-aa7e-4abf-babb-a2855bcb3fee@kernel.org> Date: Mon, 1 Jun 2026 17:25:46 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] mm/vma: eliminate mmap_action->error_hook, introduce error_filter To: Lorenzo Stoakes , Andrew Morton Cc: Arnd Bergmann , Greg Kroah-Hartman , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/22/26 18:00, Lorenzo Stoakes wrote: > 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. Is that really a filter or rather an "error conversion" / "error override". "Filter" to my German brain implies that we would ... filter selected error codes, not convert them to something else? > */ > - 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; > } Out of interest, why does dev/mem require this monstrosity? If it's really a dev/mem specialty, you could just make it less generic and call the property "bool eagain_on_error;" because surely, we don't want any more such monstrosity? -- Cheers, David