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 491703C3F7B for ; Fri, 17 Jul 2026 12:03:45 +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=1784289826; cv=none; b=lueMzCiivb8KPN4OlknPvc0xshi2lwgPir3ZKnvb+rvSuDAEEC4UskAKqE/d+kzwdsP+2mQC5gK9cDn7CNZV+k3Jz46S69W/qPnZo6KkgKJoScRu0nDG8XDZjyh0sr2xaPl0cFvvgg7xAZ1NK3op7xRZyKNH67j+HoeWSxSA26o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784289826; c=relaxed/simple; bh=qETsZFQ32d2NXuRMT2Tp4dBli40ycz4D6nxLHEVSVyA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KlDmajmFK5Kpk2PBoVvSwRdTVRrYLynr112jsqw61iwKQM8BzBMlfeJt5JcP6Daf/EZMQtAK+CpZBqCqCjd4VFTiAkQYQwuNIRo3aGWwHQ5msLrRaS6zuV3ziRei5+QwcEutgTPdIMqX7YGdsvjC0KXRwfLFWuQ6qI3/LEFmGgk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V4IK9Mop; 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="V4IK9Mop" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 085841F000E9; Fri, 17 Jul 2026 12:03:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784289824; bh=TAhO/JwnH73LXabfUU1JdQwZNZ4DmWXSeWOANj6WeWs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=V4IK9Mop8Z4A0lyJTyb4dTEk4OhMUvfuBrlVPQWj6tx8btUT40V5yJPPBIACO9s/J /qPwtJSTdmC38bpneJYSjSIq8XlgYNXg0XQtjBYoYYL+aS3YDElWEGxNL1XkTe10Tf dWihIGS8wDQZJWvcfNvwLYr6ug3TPTLSiLsYDarxOcV3TSV9jsvXXnw//SA47GFOyo zbN4J/t3KoYav2KYSUcwmwNQiJBZqzhLa36C5n7RjszOp6O2RNRkdrzXCTJbrp9uKh OrKB/Qx6sGYEcI294f9cZESghydSqQobDQJtvjllAkHa+noVz769bpDC3j8s9vHdmy jPqrmYrszcWlA== Message-ID: Date: Fri, 17 Jul 2026 13:03:41 +0100 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 v2] mm/secretmem: don't allow highmem folios To: Brendan Jackman , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, brendan.jackman@linux.dev References: <20260717-secretmem-highmem-v2-1-1f1a961ca91e@google.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: <20260717-secretmem-highmem-v2-1-1f1a961ca91e@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/17/26 11:48, Brendan Jackman wrote: > secretmem_fault() allocates a folio with GFP_HIGHUSER and then calls > set_direct_map_invalid_noflush() without checking folio_test_highmem(). > This causes a warning and process crash (vibe-coded reproducer in Link > below): > > Su[ 30.071284] ------------[ cut here ]------------ > ccessfully allocated and mapped 2097152000 bytes at 0x3a449000 > Populating memor[ 30.074614] CPA: called for zero pte. vaddr = 0 cpa->vaddr = 0 > y... > [ 30.078636] WARNING: arch/x86/mm/pat/set_memory.c:1840 at __cpa_process_fault+0x34d/0x360, CPU#5: allocate_secret/570 > [ 30.084789] CPU: 5 UID: 0 PID: 570 Comm: allocate_secret Not tainted 7.1.0-14063-g4edcdefd4083-dirty #10 PREEMPTLAZY > [ 30.090937] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 > [ 30.097543] EIP: __cpa_process_fault+0x34d/0x360 > [ 30.100514] Code: ff ff 85 c0 0f 89 7d fe ff ff e9 3d fe ff ff 8b 03 8b 00 c7 04 24 c8 ff 64 c1 89 44 24 08 8b 45 e8 89 44 24 04 e8 53 7 > a 00 00 <0f> 0b c7 45 f0 f2 ff ff ff e9 fc fc ff ff 90 8d 74 26 00 55 25 00 > [ 30.110829] EAX: 00000000 EBX: f64afe98 ECX: 00000000 EDX: 00000000 > [ 30.114799] ESI: 00000000 EDI: f64afe98 EBP: f64afe04 ESP: f64afdcc > [ 30.118785] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 EFLAGS: 00010246 > [ 30.123020] CR0: 80050033 CR2: 46c48ffc CR3: 038c8000 CR4: 00000690 > [ 30.127010] Call Trace: > [ 30.129078] __change_page_attr_set_clr+0x5e7/0x870 > [ 30.132275] ? console_unlock+0x99/0x130 > [ 30.135069] ? irq_work_queue+0x36/0x70 > [ 30.137853] ? page_address+0xd3/0xf0 > [ 30.140421] set_direct_map_invalid_noflush+0x52/0x60 > [ 30.143782] secretmem_fault+0x128/0x210 > [ 30.146560] __do_fault+0x25/0x90 > [ 30.149053] handle_mm_fault+0x6d1/0xcb0 > [ 30.151759] exc_page_fault+0x135/0x3b0 > [ 30.154487] ? doublefault_shim+0x150/0x150 > [ 30.157416] handle_exception+0x130/0x130 > [ 30.160137] EIP: 0x804d29f > [ 30.162307] Code: 89 54 08 e1 89 54 08 e5 89 54 08 e9 89 54 08 ed c3 0f b6 44 24 08 89 7c 24 0c 69 c0 01 01 01 01 8b 7c 24 04 f7 c7 0f 0 > 0 00 00 <89> 44 0f fc 75 0e c1 e9 02 f3 ab 8b 44 24 04 8b 7c 24 0c c3 31 d2 > [ 30.172936] EAX: 5a5a5a5a EBX: 00000000 ECX: 0c800000 EDX: 3a449000 > [ 30.176927] ESI: 00000000 EDI: 3a449000 EBP: bfbbae18 ESP: bfbbadac > [ 30.180897] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00010246 > [ 30.185161] ? doublefault_shim+0x150/0x150 > [ 30.187979] ---[ end trace 0000000000000000 ]--- > Bus error (core dumped) ./allocate_secret_i686 2000M > > The equivalent bug was pointed out by a local Sashiko instance on > https://lore.kernel.org/all/20260410151746.61150-3-kalyazin@amazon.com/ > > This hasn't been reproduced it on older kernel versions but from code > inspection the bug seems to go back to the original introduction in > commit 1507f51255c9f ("mm: introduce memfd_secret system call to create > "secret" memory areas"). If this configuration has always been broken, > there's no need to worry too much about feature regression here. > > Nonetheless, instead of just completely disabling secretmem under > !HIGHMEM, just drop __GFP_HIGHMEM. This means that now where you > previously got a crash, instead you'll just see the secretmem process > OOM. > > Could secretmem just support highmem by saying "this isn't in the direct > map anyway" and bailing out before the set_direct_map_invalid_noflush()? > Maybe. That depends on requirements that are not well-defined (e.g. is > it OK that kmap_local_page() is not a NOP for those pages?), and would > require some research and deep thinking. Let's "defer" that until > an actual usecase arises. > > Link: https://github.com/bjackman/limmat-kernel-nix/commit/7b2acba2d3a5ef01400d493a155beb1d135b6bb5 > Suggested-by: Andrew Morton > Link: https://lore.kernel.org/all/20260704192603.40aa80cf9242b77aa75e8d8d@linux-foundation.org/ > Fixes: 1507f51255c9f ("mm: introduce memfd_secret system call to create "secret" memory areas") > Signed-off-by: Brendan Jackman > --- > Based on mm-new with `[PATCH] mm/secretmem: disable under HIGHMEM` [1] > reverted. > > Note this was found by Sashiko but in a local instance, so I can't > provide a link to the report and I guess it's technically inaccurate to > mention sashiko-bot@kernel.org. We sometimes just used Reported-by: Sashiko ...without a link report. Acked-by: David Hildenbrand (Arm) -- Cheers, David