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 2D41F41CB5A; Thu, 24 Sep 2026 08:19:44 +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=1790237985; cv=none; b=EiY+e9Sid0QaUhwz+cqpqlWDtoYLv3oP7yt+RdxIPi9KIzvOa6xm76q4pPC7VGrs0q9Bb/tP+yNsuO1CY4gxW8s6ZjzYr+6+gwO1tkJyaETlG9yevTnjBeNN3jkT3t+y0gR/P1beXLbG433uEIFrhn0txbKCjUsGQ1H+eu92myI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790237985; c=relaxed/simple; bh=WImGzSPhUQrfFfdTg4EMX+LlTIkR51MI4LJsWWS8GTE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MGVyUsuGBqZeBYUfM/jMCsS5ozon+jxMDrrXCbLSXAnmoLHgqXjkQqHNaNCLfe2ZqzMgeZyVai/iFfk5a64Mhi7UdTScJKQDfKKzEaVeOrQsnRpZRI7SsWrnzT6BLvoG8tUtWBp8t4czoPEYyUd1gaXcX0DSJGaP0bD+Rl22dpk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n+gQShgo; 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="n+gQShgo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0BEF1F000FF; Thu, 24 Sep 2026 08:19:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790237984; bh=j38sKxcUuo+v+Xf2oFDiECaiMijka26xvcA+axqRQxY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=n+gQShgouLNB4db+aIgFmU0669lvvGgyqD5kLZaf6uVg42XzHAnFT+lXpFJw9bJKb EO1Bjtpb6VPH/M/4BVZKIF8ezAVotbvVw8WTP+tW7F7BQrt3if0KdoQ6pQ47M1GMdH TXRFzeOPvpjVJbZM7hixJhvVnDv+asJOWGsjGrSOyCVwDX7k2TE0Iqih5KSeCNZ1n/ savoOMzeKelYBBa5rpykQ3V84ZCeIBG69Sj7aXKVzhDzOdo1rW4d1WvT8pPU+PZroG ppFv+Rwl1qgTNwaPNx/AA9iHYcGixy3TEbTwZAglGLRyta1LNgIqUlzPACmUYjrV0Y VrBK2DVCZG97g== Message-ID: Date: Thu, 24 Sep 2026 10:19:33 +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 Cc: Andrew Morton , Alexander Potapenko , Marco Elver , "Rafael J. Wysocki" , 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/23/26 17:49, Mike Rapoport wrote: > On Wed, Sep 23, 2026 at 12:31:26PM +0200, David Hildenbrand (Arm) wrote: >> 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. > > Naming is hard :-D > > I feel that _copy_page() is to vague and adding hibernation there is to > mouthful :( Yeah, I wouldn't mention hibernation. > > And these could be used outside of safe_copy_page() someday. > > How about > > kfence_set_page_present() > kfence_set_page_default() Maybe spell out "direct_map" ? kfence_set_direct_map_present() kfence_set_direct_map_default() But yeah, something along those lines is better. -- Cheers, David