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 8382933689D; Thu, 1 Oct 2026 11:33:14 +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=1790854398; cv=none; b=mgf/5KrwamAPN6X6uPLE1mriwwIaZlNb3QvzI191cx5urFwVMsS0rinr91dOo5ONguCfuitcxBRHgHNTqlHvdirFJdRPCbHxLQRQsI9XT43Jb27TYQPEoO3T1zzTgyQlKFgKkffyVTFZdUSAfUHRFjEXHNdRIYqfAHZOU9v36mI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790854398; c=relaxed/simple; bh=Ju4zJ/F1idepavt5dJkVNJFsVLb+meNtjLKbBCIo1/A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AAN6mqxdZNy194YbJprqAhCDjnfxR8t+K/ik1T06cWY0K9WmI1bb3x4pIm72EUN1kZzKhlBK3RNiA5L/Lly/q5Cwd9z5ojfh4Zc4Kn1nT+9Ay3f3ApCblP5K54okY6FKyVZsU1ZQK95nYD+G3ZYy10TZIDOVpStAmsz4lIMH/go= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iD53Oifp; 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="iD53Oifp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3039A1F000FF; Thu, 1 Oct 2026 11:33:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790854392; bh=b2hY2Lwa9e4ug6tiGWzP7cLmTEKbjt1EVVbwD8WgJqc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iD53Oifp/0W8HMOSNW9RLwVbugDqNyDtJoq4TPv4O2H+BOf7+CcJKqPB1nG0G9tg4 Ou+C2O2JlfDb7vpzb7HfDkraQyJ++Upwa8X8TTgcD6F+Ze956QW97elz7kK4l/gbzY SWdxBw6KMHjiH6PnnGJhkq1Sjz751s1sMCP4N/GD1rEBqE5j4tjvdsDniB+5d5JStZ ygajxJTAvJFlo/QWoLABdpjnQ0OIGs1pIeksWHX1R8jWoMvp1fKOpKwMd24oe1/GeU MfPXizuEjQRxBTnxQy6GWVhaO3YwSTyWDkV6mriRPMOVVa1Xc9P2kVv7Wefp7PZRR7 /qs2Z/i1dQ5zA== Message-ID: <7454d7a3-57c6-4883-a66b-26129e633c6e@kernel.org> Date: Thu, 1 Oct 2026 13:33:02 +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 4/7] maccess: Use a scoped guard for page faults To: Muhammad Usama Anjum Cc: Catalin Marinas , Will Deacon , Mark Rutland , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" , open list , "open list:BPF [GENERAL] (Safe Dynamic Programs and Tools)" , "open list:MEMORY MANAGEMENT - CORE" , Viktor Malik References: <20260824160523.3907021-1-usama.anjum@arm.com> <20260824160523.3907021-5-usama.anjum@arm.com> <79daa73b-0d34-4e84-8450-56f90bc700d4@kernel.org> <98e9ac67-7df3-4c0a-8814-37e196d94020@arm.com> 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: <98e9ac67-7df3-4c0a-8814-37e196d94020@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/25/26 14:07, Muhammad Usama Anjum wrote: > On 25/08/2026 11:36 am, David Hildenbrand (Arm) wrote: >> On 8/24/26 18:04, Muhammad Usama Anjum wrote: >>> Kernel nofault copy and string paths open-code page-fault disable and >>> enable around label-based loops, duplicating cleanup on success and >>> failure. >>> >>> Use a page-fault scope guard instead. Leaving the scope now re-enables >>> page faults on both paths without separate cleanup at the fault label. >>> >>> No functional change. >>> >>> Signed-off-by: Muhammad Usama Anjum >>> --- >>> mm/maccess.c | 53 +++++++++++++++++++++++++--------------------------- >>> 1 file changed, 25 insertions(+), 28 deletions(-) >>> >>> diff --git a/mm/maccess.c b/mm/maccess.c >>> index c59a0e092d24a..f695ceefe6fcc 100644 >>> --- a/mm/maccess.c >>> +++ b/mm/maccess.c >>> @@ -38,18 +38,17 @@ long copy_from_kernel_nofault(void *dst, const void *src, size_t size) >>> if (!size) >>> return 0; >>> >>> - pagefault_disable(); >>> - if (!(align & 7)) >>> - copy_from_kernel_nofault_loop(dst, src, size, u64, Efault); >>> - if (!(align & 3)) >>> - copy_from_kernel_nofault_loop(dst, src, size, u32, Efault); >>> - if (!(align & 1)) >>> - copy_from_kernel_nofault_loop(dst, src, size, u16, Efault); >>> - copy_from_kernel_nofault_loop(dst, src, size, u8, Efault); >>> - pagefault_enable(); >>> + scoped_guard(pagefault) { >>> + if (!(align & 7)) >>> + copy_from_kernel_nofault_loop(dst, src, size, u64, Efault); >>> + if (!(align & 3)) >>> + copy_from_kernel_nofault_loop(dst, src, size, u32, Efault); >>> + if (!(align & 1)) >>> + copy_from_kernel_nofault_loop(dst, src, size, u16, Efault); >>> + copy_from_kernel_nofault_loop(dst, src, size, u8, Efault); >>> + } >> >> While I understand what pagefault_disable+pagefault_enable does, it is >> completely unclear what scoped_guard(pagefault) does. >> >> Should this be scoped_guard(disabled_pagefaults) or sth like that? >> > > The `pagefault` guard is already defined in `include/linux/uaccess.h`: Ah, sorry, I thought this was added in this series. It's completely confusing. guard(pagefault)(); meaning "disable pagefault", what?! :) CCin Viktor: I see that the patch that introduced that has no acks from MM. I don't blame you, because the file is not actually listed under the MM section. I think this really needs to be cleaned up to clarify that we *disable* pagefaults. Usama, can you throw in a patch to clean that up? (calling it nofault, disable_pagefaults or whatever) -- Cheers, David