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imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="XBFwv/J0"; spf=pass (imf10.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771401158; a=rsa-sha256; cv=none; b=ldKr0J4AzqDVBjjLXT0htdkCeRvm9dEdt/JpAoWS84IFxW2TI0GHFE5ZZjJAD/866hbpBK bsdb5YHwZEBa3677PwS1Sdtm9DtuEzLWrupaOKxpL1sjXCLCpdsnNjw53qvBr6T88ZyHBt yTActf3F0SVH4bmqTS41YemAuCgGaoI= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 3047B600AE; Wed, 18 Feb 2026 07:52:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49BC7C19421; Wed, 18 Feb 2026 07:52:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771401157; bh=xHxjG4bDz4pgMox2OsAsfkgSSmmHF2eogXtvvKL0pkM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=XBFwv/J0DHxfil/5yD6SPFQuYpECUHR5ZkFwRRYUuYJigiix4wzFkNC0ctIpYoBzr +B033FA2rkhfJBYWqPcqOcPyi+uvOk3iTMIFgQwOScyB/0CPD3YFTxLJRUCUQ2fwiF lx1Z61wkbIIabzOlIbr6+HAJ3RdLhPJuOLL+Lzb7hxNEusLBuOETkfMOZgrRp8akR/ iiOUz7ij/AH7Lu4BDp0/PXkbshEP+BDDL0M+SFKHh+4BxJq9glypyjclCQasxxJDAk nW6P7XLVtdmDlnomvjPB9+HnqAAPIGYomS1z5G9i8fux+VWWPhtrgYO+ocIaj6qL/4 4F3uFGDQRXr8w== Message-ID: <0b653dcd-842b-4360-bc1c-8fe779efbc23@kernel.org> Date: Wed, 18 Feb 2026 08:52:33 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/huge_memory: Fix use of NULL folio in move_pages_huge_pmd() To: Chris Down , Andrew Morton Cc: Matthew Wilcox , kernel-team@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: 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; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 3bcextcdyb1hkhxmi8cphest14j5x7xt X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: E0A2BC0002 X-HE-Tag: 1771401158-709805 X-HE-Meta: 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 CvUBIGa1 xH8teBSXa2tME1hyaT8usj1mgpZUJBPBPq8Me3EZGJPBIVwyG3eesoAc1F8FMkfF0S5PdIXt1waUbd0wMCQ1lR6dZ9TkS3dQPCgLOuIPL6hUtO13tw0JzyvBqDohaeacOYQXL93yxTJgyr4tgkI0ZaCSwqBDqeytItcOnzN8sz91bwr1mVYyVi6IVxVII8H9f3o76vSgcldAUPhYMOzu4yZFAY64CjHjMKcvSqmFdWVCl3NQN0KoT4wQld11DQjoSKteBZgptMAH/iBzWfzjmdeg9hZJK/TvIkSydbYpFNuS4F/zNS1ybjBICzA8YRNyWhWJqCg8QAouSJWw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/18/26 04:45, Chris Down wrote: > move_pages_huge_pmd() handles UFFDIO_MOVE for both normal THPs and huge > zero pages. For the huge zero page path, src_folio is explicitly set to > NULL (used as a sentinel to skip folio operations like lock and rmap). > > In the huge zero page branch, src_folio is NULL, so folio_mk_pmd(NULL, > pgprot) passes NULL through folio_pfn() and page_to_pfn(). With > SPARSEMEM_VMEMMAP this silently produces a bogus PFN, installing a PMD > pointing to non-existent physical memory. On other memory models it > is a NULL dereference. > > Use page_folio(src_page) to obtain the valid huge zero folio from the > page, which was obtained from pmd_page() and remains valid throughout. > > Fixes: e3981db444a0 ("mm: add folio_mk_pmd()") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Down > --- > mm/huge_memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 44ff8a648afd..fed57951a7cd 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2794,7 +2794,7 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm > _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma); > } else { > src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd); > - _dst_pmd = folio_mk_pmd(src_folio, dst_vma->vm_page_prot); > + _dst_pmd = folio_mk_pmd(page_folio(src_page), dst_vma->vm_page_prot); > } > set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd); > God this code is horrible. Why can't we simply move the PMD like move_huge_pmd() would do and make this code less error prone? _dst_pmd = src_pmdval; According to validate_move_areas(), the permissions of both VMAs are equal. We might have to handle it just like move_huge_pmd(): _dst_pmd = move_soft_dirty_pmd(src_pmdval); To also set the softdirty bit. Then, we would want to just clear uffd. _dst_pmd = move_soft_dirty_pmd(src_pmdval); _dst_pmd = clear_uffd_wp_pmd(_dst_pmd); -- Cheers, David