From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 E0D4635A398 for ; Thu, 1 Oct 2026 12:32:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790857977; cv=none; b=IPj+DbX4BdS16B/ZMJHEXMEQXJnH0t4s8wznIIhzOpAHOVIxC5k9LafaEp04qFFOVG0USWr0uFpqg+hnIFvex4IbxycqaFlYXzTKmHtpjekpiYMZyI2rZbkImLgK8tTtmB3gvGfU3wDY/oZ9fnTA+std6vV0O9cqPObEERi9Y8Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790857977; c=relaxed/simple; bh=k3JA2v41OnZ7UfxKKtnSfTR/W9JbMqA8ZaWuRot9ZAA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OJWP0EnJ4o0vyMl4CP4uvdcjrZhgXKJGTyg41Lr76/2h/ewTNAJwmGXpAHtJzFkZ2CcxXvt9yIrn/qq17IPbhl7H9EqggEyXsn5Ihs3CmXpKfavEziHkwXy6oLhU92hHmuqwDPPBTljpwUOPPyqdmz/mZ9i8U+jX+ccYfMOBWgw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=PL2OYIR7; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=c0JgCYmh; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PL2OYIR7"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="c0JgCYmh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1790857973; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gMYtf80P5oX4IkVB/3A4AGGwzt6DCWZzJjMZ+oV75Lw=; b=PL2OYIR7qszlw8p5iaW6Ddl11UDYi4Pf792PkKrqBeitjAQzxL0zOBucLuLgipBV4lVTqu ubC+8SAI9ng9VkFRTNn89BTslOlm1zAWxxc3TWOUUthNh4EGr7Pxbhtmn82euJScpWc2oC azRg/YpXB4oahyfH/LvnOM83Jg2WXOg= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-509-JQhyqWOwPpe4yrvkOHRUnA-1; Thu, 01 Oct 2026 08:32:52 -0400 X-MC-Unique: JQhyqWOwPpe4yrvkOHRUnA-1 X-Mimecast-MFC-AGG-ID: JQhyqWOwPpe4yrvkOHRUnA_1790857971 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-48b027578a4so1611838f8f.3 for ; Thu, 01 Oct 2026 05:32:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1790857971; x=1791462771; darn=vger.kernel.org; h=content-transfer-encoding:content-type:in-reply-to:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:from:to:cc:subject:date:message-id:reply-to:content-type; bh=gMYtf80P5oX4IkVB/3A4AGGwzt6DCWZzJjMZ+oV75Lw=; b=c0JgCYmhlu+QLKm+uCK++ues4PWTYV2OQEJ1L/r62kEcm4Bu7eOmmidsjBvAlTGx5a /PWM0BDFiD6CDTT/3qdGfBwtMNvBJ1jUv9S/pB59cUwfilHFYM82WZ3XfAm8a/p92606 yT3ce8N5LHQle/RHsGaVHj36r0so3jZ3CSQcSdmuWh07+2VbvVnamzvdgaT2UfDn2wkn ir32+dtt38zfwsLZnZQlxHutbm0Htn4yT9Uv9VzSMco8ouojq6Y64lL36WVO8bG0QSGt 8GpbNNxAVvPPOn3b5nrpLg5q7E6zIbYwCnA8bEkjtrkGolBEJyiYDbf4XY8e9V0YRyc6 i4gQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790857971; x=1791462771; h=content-transfer-encoding:content-type:in-reply-to:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=gMYtf80P5oX4IkVB/3A4AGGwzt6DCWZzJjMZ+oV75Lw=; b=uRt00sCZF6Gy3dpyjGt4EuEaAuIOUqYmha+FGrebwdyQTMYqh5oEjCVHGYfYt71m/u he3OS/ER+rKbZ304ctQIrrmy/UYGo7Sbgt6ID6SS12Jn+S5KvaG2cLe7Cly3hKJOAf31 JXadMih3m3ewD36EjvelE0+89FzxauxdKS+BLQKziGbncrAEg18pc92nHq0ODTvARDgt 3Qz5jh5cwFNPuQTLeyVJ5i0dXy/65lyK5cQB5x3ua5PSXph7KWWfz+IizOuOEhJhlGok wGQjSVNYJr2sU2B0DCWuPXWi17XLd2blYtHpBDKSQ7ZQF7+X8IB4c70F0B1mHfLTYGDB xc5Q== X-Forwarded-Encrypted: i=1; AKwUvBw3o3Pzqc9xtEfcG+8D98qXiBbBfpDbULIgDiIJNDC1hA/wnLGvnGOQHm0FfayQmWFB9bg=@vger.kernel.org X-Gm-Message-State: AFq9FYJH3ykkNpnfXKOw85fm0crwt6YtXwNYOxRIBX8cj8WJoEA5qavu bXan/Yoc2XNH7KSZ1K01bhbVic9V+g/sGM9lyJHzuHlyG8wje0guYIktOupXixjq2OdZawaiCTx xsK7S+maVxCtq1RrJ8Dfe1POXt8W+2PV9Vbaz7HzUX0jee6F5RuHr X-Gm-Gg: AYBFou1++LsTi+uFTgV/AoFIpTuSzBta5cGgfYdrI53zlJMyIsVriNDklzWdn3SioOa W7RCzXlaeR9C2Ij7l3mJWIIugiLGGDotWp9FiSwrx/fXTE9V5znykIl0d9NmYVD/rZXRMQcHUix SInOUS4SNcPXZ4OWL7MlBVRocPuAy5QtjvL4/2jZsZHSZwCH+sLE5uvoovo/5T6k7zH74kHJRxw hVLNYwvKQOfdza8cR/g1QOyC8iOrWfFOOXirCn3mCJooZE08xl7+K+455u83Z/cKC9q6NvDlauW HXxwM9r5PHQjrzjQOSc2T/O4wb1bz6UjVlzWyRYGLkE9hUlylUXBR2AOjj8X7EFI18T8O0YFP5C b9k8NzENkKjhUqHkC3cVRMvH94V5cJhctMQ== X-Received: by 2002:a05:6000:4107:b0:485:ac35:5c5d with SMTP id ffacd0b85a97d-48b05870bd4mr4665279f8f.15.1790857970828; Thu, 01 Oct 2026 05:32:50 -0700 (PDT) X-Received: by 2002:a05:6000:4107:b0:485:ac35:5c5d with SMTP id ffacd0b85a97d-48b05870bd4mr4665181f8f.15.1790857969830; Thu, 01 Oct 2026 05:32:49 -0700 (PDT) Received: from [192.168.0.101] (185-219-167-205-static.vivo.cz. [185.219.167.205]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48b0691d681sm5371173f8f.23.2026.10.01.05.32.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Oct 2026 05:32:49 -0700 (PDT) Message-ID: <5e183c24-4acd-4b79-b601-bd1aa2f53dce@redhat.com> Date: Thu, 1 Oct 2026 14:32:46 +0200 Precedence: bulk X-Mailing-List: bpf@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: "David Hildenbrand (Arm)" , 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" 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> <7454d7a3-57c6-4883-a66b-26129e633c6e@kernel.org> From: Viktor Malik Content-Language: en-US In-Reply-To: <7454d7a3-57c6-4883-a66b-26129e633c6e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/1/26 13:33, David Hildenbrand (Arm) wrote: > 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. You're right, looking at it back, it's a really unfortunate name. Renaming to nofault or disable_pagefault is certainly better. Thanks for pointing this out. Viktor > > 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) >