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b=Dg1fRSCg7k3Q2cK9Sat615Pj7Jh0PALjT32x9LczwQkRJEkfcOlRGlQvCq/OfhtyQ SU+aTqkoeOQMHGt6s/Oc6VC6xrwccygDUgzu9ii4MyuDMtNBqzDgwChPufMaqkCzgW uLHQuo0VgJ3QxnXTbIKkqcDWrcpBEy9VrmC46MD+elXPqK08UWyEego0mwNh+rYb/U S+LE3hsOmSqxwHWQdTfhsAZKOCUtomSxdHJr83Lo6JxATY49GUAn2ORLbpCLhZgnQh TkKAV3TTOwTwKGZmUrAHcmNEPdLEWUEV4ebP7hEtgoRnhX2bnpA2vQ14qhuC2nWPu2 EjcdY+vRMEt9w== Message-ID: <7da49940-e1a4-4018-9db1-208411598e77@kernel.org> Date: Wed, 25 Feb 2026 16:23:29 +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() From: "David Hildenbrand (Arm)" 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: <0b653dcd-842b-4360-bc1c-8fe779efbc23@kernel.org> 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: <0b653dcd-842b-4360-bc1c-8fe779efbc23@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam09 X-Stat-Signature: w7ckknamjqhg9whh9q1pj9aaa5h7cm6p X-Rspamd-Queue-Id: 058A1140002 X-Rspam-User: X-HE-Tag: 1772033013-701056 X-HE-Meta: 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 dGOXna/q J6fGoPbNyBt/NHw7BLS88+08O5heFTSro4JBEUuL6wube7CqLPNDqcyx25p775oNKHiP1VPHnMbAlIi1o1hMXIZlCMiorVQ7fr2jb0TVv7JKPggs9JlCXF2CIMZJ/3xTyOs7Lbue/4HANMib84Su+nayqvt9bHKApWxnvHtKf8RzYaBf4WkcqYqdx3WyOnU6qUxwRj2fio1eikEKcduYNxHWm7bI4kraPGdYWi+Wxx3qqQTKTb7VrAM5xeb6aiAOIaSCJ+/0FzPKDFSRa9dwbsKmTmEd4vtUU4+zw8MAFIbLwtgjVWV+XX7+tnT/PPxP0N8Po7vjBcJH3AJkcGSNAUkiBtWz9vn8FwZ8F Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/18/26 08:52, David Hildenbrand (Arm) wrote: > 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); > Chris, do you have time to follow up, or should I look into it? The issue looks quite bad, so we should tackle it ASAP. -- Cheers, David