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b=mvqsq0kUH13XZgmV8wElxnONJYeKXRqcfRRtYItlQjBVZKxpIE/dc+ITxNhd6S1p3 T2AjMG/TXthk8J2aulk2q2MatA2xW+lUiBrhq/dJfzPp0Tvh1M45a6xqx+nCoimZB8 Pa2p1cUOqejG1LVB6MWXxv7ibGazvHkWUonN7OkkMkvDkN7+rPQj7hKLdKOjCbSJgJ Qs3pYm9sEqtL0C1RQDAZtPzelk+G+G4c8UXhxne2nTIChYjR15eVMDKR1l7R9/JRD3 WkhmvwuAcYqgQkKVomgYxqh5obrOaPBcUtP6Y0HGiJQzdwcykcopRA2JFm+oEdE2Gg 4xNbTcjO4nhSQ== Message-ID: <6147cf80-9d02-4c5c-ab81-8cb9b00044f0@kernel.org> Date: Thu, 26 Feb 2026 16:17:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm/huge_memory: Prevent huge zeropage refcount corruption in PMD move 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 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 91A2D100005 X-Stat-Signature: ff7hmkmjxgm1upjz35jkzywprg5w781y X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1772119057-361383 X-HE-Meta: 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 +qsPphPK SDVUY+kv1AVpqb0Ed4/dw8gJVDt1BQ0OpHwAcL6BKhWHfnquu+u7JTJlvIjw6pSYUtxummS0mRCJ0cOhATamYJukDRa/Bc+RCwK1foSY6NRfUAQ368S/fjexdL8nPdolNCmJZkK+gbi2K6slDvV45/suzjalKtlMRVtDeBvYH+H+Peceipcal3rcUyWuFP2lWJDFFDx1ZNC8Emu1xBVk5LN7Ptr6yjb+8fTahHadC+PxW+n5KtAfhgZqTjJkHfHwszxxl+RbC3TVZSMvDw0JKrBy3a+/06V8s7IxyDj8Itra0P1R/8xOABoodOX7jKfEdbHD1CE3OqDUXGDY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/26/26 15:16, Chris Down wrote: > After commit d82d09e48219 ("mm/huge_memory: mark PMD mappings of the > huge zero folio special"), moved huge zero PMDs must remain special so > vm_normal_page_pmd() continues to treat them as special mappings. > > move_pages_huge_pmd() currently reconstructs the destination PMD in the > huge zero page branch, which drops PMD state such as pmd_special() on > architectures with CONFIG_ARCH_HAS_PTE_SPECIAL. As a result, > vm_normal_page_pmd() can treat the moved huge zero PMD as a normal page > and corrupt its refcount. > > Instead of reconstructing the PMD from the folio, derive the destination > entry from src_pmdval after pmdp_huge_clear_flush(), then handle the PMD > metadata the same way move_huge_pmd() does for moved entries by marking > it soft-dirty and clearing uffd-wp. > > Fixes: d82d09e48219 ("mm/huge_memory: mark PMD mappings of the huge zero folio special") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Down > --- > mm/huge_memory.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index fed57951a7cd..8166b5e871ad 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2794,7 +2794,8 @@ 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(page_folio(src_page), dst_vma->vm_page_prot); > + _dst_pmd = move_soft_dirty_pmd(src_pmdval); > + _dst_pmd = clear_uffd_wp_pmd(_dst_pmd); Please squash that patch directly in #1. It doesn't make sense to leave something partially fixed in #1. It's been completely broken from the start. folio_mk_pmd() should never have been used. Apart from that, the end results LGTM, thanks -- Cheers, David