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 C1E3D488233; Wed, 23 Sep 2026 10:31:36 +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=1790159505; cv=none; b=GjEwyPsKS+PIzPhuUbUNiyw6rTOlFIR5LmKPLuVX3BNdgYwe0AW2OZ2OQoLRcVjq4KuNcc5rO/StXjBBDyQDkWu1G5O0ttELvj5PuTRp3u9zLLt91PEvzzKzBYifYCCdlLPayBuR+MYnbH7UXdriHDoEQly08Q4e6Tln8HC9aGA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790159505; c=relaxed/simple; bh=puhRv8cvCWPdt+898drsZ6gAREbajbbq2Kz8e2guv0Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PfBJy+kdeLLd3ysuLeXQHa5RrADUKQ89Tn7ZiXOS/cD1FJik8ABUBWKBGCTR1doVSYKRNYRqF1o+zvlgyCogloPTqkVicCnHS6LO1pG1CX07GGHToed7umcVMG72cYuTkKqWTQIWmaVKhHX7vLKtmuepfJH3ShHjJnQvNDYWxq4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=j35rH4u7; 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="j35rH4u7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8271A1F000FF; Wed, 23 Sep 2026 10:31:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790159493; bh=aF1MzpU61XRmUHcDP/fvbQ0mXhibmF/LWQ0namfOZ8U=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=j35rH4u7WV13DsI7KZ4JrOlt1/NTCQO5zUuJnhXsK3azEtUNgmnX59lKPmMfjDbqL Fwqe8wTPPPEo4297dLRg9aCSd9xpep8/RXoK1N1AHdEpiamQgo7zuQO/WC+8VWA9sy u6XdogA3R/SrEmjk3/ffko7jtDTgCzSBCpRQ9ruCfYu2ycm4tOrU8gqh4q6sD2pvaK RZX2znjko45SxPIZ9lGTG4v+DXBdne6J5DWcUpX/3H254Ur4VgR/UbBlo8nnzwPnl0 Wmh2/efj9MGLgcFXE5euNPTX6V1vm8LLCaCO+xMIJxghSoX6v/6h57QTv/ffZNdzRH +DgjaGBeBMM9Q== Message-ID: Date: Wed, 23 Sep 2026 12:31:26 +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 4/5] hibernation, KFENCE: explicitly map/unmap KFENCE pages To: "Mike Rapoport (Microsoft)" , Andrew Morton , Alexander Potapenko , Marco Elver , "Rafael J. Wysocki" Cc: Dmitry Vyukov , Len Brown , Pavel Machek , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org References: <20260917-hibernation-v1-0-7f7dfae3dbe0@kernel.org> <20260917-hibernation-v1-4-7f7dfae3dbe0@kernel.org> 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: <20260917-hibernation-v1-4-7f7dfae3dbe0@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/17/26 08:07, Mike Rapoport (Microsoft) wrote: > The pages protected by KFENCE are removed from the direct map. > > safe_copy_page() temporarily maps and unmaps them using set_direct_map > APIs, or, when the stars align, even using debug_pagealloc_map_pages(). > > Neither of these APIs cares whether it is a KFENCE page and both blindly > perform the update of the kernel page table for any non-present page. Agreed, we should route this through the actual mechanism that modified the directmap in the first place. > > Ability to use debug_pagealloc_map_pages() to remap KFENCE pages when both > KFENCE and debug_pagealloc are enabled is an amusing coincidence. > > But with increasing appetite for using set_direct_map for hardening > purposes, it becomes too big of a hammer to enable saving any non-present > page in the hibernation image. > > Another gotcha is that loongarch that does not have a direct map at all > advertises ARCH_HAS_SET_DIRECT_MAP to allow coexistence of KFENCE and > hibernation. > > Extend KFENCE with a bitmap that tracks which pages are protected and > provide kfence_force_mapping() and kfence_restore_mapping() APIs that allow > forced mapping and unmapping of KFENCE pages. > > Use these APIs in hibernate_{map,unmap}_pages() for KFENCE pages. > > Signed-off-by: Mike Rapoport (Microsoft) > --- > include/linux/kfence.h | 29 +++++++++++++++++++++++++++ > kernel/power/snapshot.c | 7 +++++++ > mm/kfence/core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++-- > 3 files changed, 86 insertions(+), 2 deletions(-) > > diff --git a/include/linux/kfence.h b/include/linux/kfence.h > index e5822f6e7f279..33a126cb6d1b7 100644 > --- a/include/linux/kfence.h > +++ b/include/linux/kfence.h > @@ -222,6 +222,32 @@ struct kmem_obj_info; > bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab); > #endif > > +/** > + * kfence_force_mapping() - make sure a KFENCE page is mapped > + * @page: page to map > + * > + * Check whether @page is protected and map it if needed. > + * > + * Requires: is_kfence_address(page_address(page)) > + * > + * Return: > + * * false - failed to map @page > + * * true - @page is mapped > + */ > +bool kfence_force_mapping(struct page *page); > + > +/** > + * kfence_restore_mapping() - restore mapping of a KFENCE page The name is misleading. You are actually restoring that the page is unmapped/protected? kfence_force_mapping vs. kfence_restore_mapping is confusing. Can we find a better pair of function names that describe what is actually happening? Maybe something along the lines of kfence_prepare_copy_page kfence_finish_copy_page That rather expresses what the caller intends to do. -- Cheers, David