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 8B6B2CA5FB3 for ; Thu, 1 Oct 2026 11:34:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A2D046B008C; Thu, 1 Oct 2026 07:34:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9DD306B0092; Thu, 1 Oct 2026 07:34:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8F3116B0093; Thu, 1 Oct 2026 07:34:41 -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 643EC6B008C for ; Thu, 1 Oct 2026 07:34:41 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 79C8E403BD for ; Thu, 1 Oct 2026 11:34:39 +0000 (UTC) X-FDA: 85273849878.30.83E5CF2 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf26.hostedemail.com (Postfix) with ESMTP id A5F15140009 for ; Thu, 1 Oct 2026 11:34:37 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="hU/U6Fzr"; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@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=1790854477; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=OFUfBJhfs43LK2uJ35trWg6Dxj/vYrf6yAbtRpo/I9Q=; b=4TsbcxY6uKRUCLS4H6ev4Nh1+8AryJYKhLCakP5Z28DKc8+G0Hmal95ycqyHr0K7rloHZ9 mhjHiRnW+dDEr98BRxG7oNYZfdzxTNSblFb0Udv+YCrWWJoHFowj6MI4F02xd6OsF1HRIj bGO6QSCkmQq8KjnP6CFbl+bMn65M0vQ= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="hU/U6Fzr"; spf=pass (imf26.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790854477; b=ECYfGzqM/VW1Y/JpTUheq+DAIjUN7oNTxgOGF63yfMjZClX31fXzM6YGTaLGNo5ybfiH1K 4F8mVrSywFJZwtGTSPhfVmPT6oIRGoNbppuZlcddfjcsf84NyNiZBYhNI6wro+7lj7Mph+ utk1j1z2zazlJYTFQebFqKzl2v/McLY= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id C98D941745; Thu, 1 Oct 2026 11:34:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7079C1F000FF; Thu, 1 Oct 2026 11:34:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790854476; bh=OFUfBJhfs43LK2uJ35trWg6Dxj/vYrf6yAbtRpo/I9Q=; h=Date:Subject:To:References:From:In-Reply-To; b=hU/U6FzrcmDrLuYwspEuImByZobXbfI3VhwI7ef+aDvD2f2HwXe2U0G2qGEHQJzu6 fgcV7rEMPAoLLQN1Q2c2AXy58ZQUD8hIexEoci4gM6Ih/uiXQxHxNonUVR69E6Z8gX ZTd2WblSoo4EGpHGIeFX6HXyLNzS/Cdpm+hpU9rUMMXmjb05OM36DMx4SfGLcf0gsY Xd5ro+jXBJIF3mVya4X9/ghB9UFUxuxmCPjf3cWIEx2a3tmZoAqGLQznV8tA3UPEsW K4ktT/2AdvhFaj3l0TnW65UsRSRYVUOIcQe3dCdHOI6V/iROn3Thy4HYnYpDvZky5p AYOKVxe1+r+vg== Message-ID: <10fd28a8-04e0-4e50-860b-ae094dd1e008@kernel.org> Date: Thu, 1 Oct 2026 13:34:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/7] maccess: Skip setup for zero-sized kernel nofault copies To: Muhammad Usama Anjum , 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" References: <20260824160523.3907021-1-usama.anjum@arm.com> <20260824160523.3907021-4-usama.anjum@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: <20260824160523.3907021-4-usama.anjum@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A5F15140009 X-Rspam-User: X-Stat-Signature: gqt8m5ebj5apt5xwxsk1gho5k6qdfojc X-HE-Tag: 1790854477-34976 X-HE-Meta: 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 TgmFzmHH 7auKgoi11Zw4N1NtzQewir+VpRZwNZ7m7ZCwD70raWfYc07HIyzOTa4sToNZlecK4qnQpLdTtkfMLkHweBI/uQHD8794QQ6Tpx2kSlaame3B+9EiB79WbIwfpf37S1a4BDUSjMkpl950At6yWpK9DnW9sPexSjQNZBn/o3Bw0eyOvXpTFp14JCZm21JnpXEo1MlOKLxV4gRCZCaCzq+myqctih9Btb9juz1YiFi7NCZEZUaGWrCV9T8J4Hzc+KiTdqn21s9YRAMpqhGIIFYzvRBd5ddKB5Vg6BY8oSggdPK0i4H4KrtFpOnecdqGUjNlTfV2m Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/24/26 18:04, Muhammad Usama Anjum wrote: > A zero-sized kernel nofault copy does not enter an access loop, but it > still disables and re-enables page faults. > > Zero sizes are valid. BPF probe-read helpers accept them, and KGDB memory > packets may carry a zero length. > > Return before changing page-fault state when there is nothing to copy. > For reads, keep architecture-specific address validation before the fast > path so its behavior is unchanged. > > Signed-off-by: Muhammad Usama Anjum > --- > mm/maccess.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/maccess.c b/mm/maccess.c > index 486559d688583..c59a0e092d24a 100644 > --- a/mm/maccess.c > +++ b/mm/maccess.c > @@ -35,6 +35,8 @@ long copy_from_kernel_nofault(void *dst, const void *src, size_t size) > > if (!copy_from_kernel_nofault_allowed(src, size)) > return -ERANGE; > + if (!size) > + return 0; > > pagefault_disable(); > if (!(align & 7)) > @@ -65,6 +67,9 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size) > { > unsigned long align = 0; > > + if (!size) > + return 0; > + Worth an unlikely() ? It's the corner case. -- Cheers, David