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b=SV6ZPi3QftK0oV2Gw/ZjShiSD8DhHQfnS0q9dpTb9QiYvt8knlldRIQdeORlYRrrH boZVHI4N5aKytFZV8uq7EqXnyyyfM95ebPJhxukUDkylzkw6ofLYO/juXjufbPpmYK brlsiftVFH0HhMWfGUfCbVyWKFZ0Exueq8QT4VFtakdynnCMjtY9TasLlk61qOeRKt O9iOCnUuHZKDOT8EbtECSIeqy3kKzr67nDf6LtjOFphMbAxMmRZ/jz4VbYk7UfVIup yuHDR0oVKXLXHfNPqjJPiDmEh8e+RJagNPHMT6Qu+HKWi2xHvU8lRcBTZj4cip1h5F VsHi7+XTlhBbg== Message-ID: <7fff15cd-5136-418c-a8a4-b9fe5f30ad81@kernel.org> Date: Mon, 14 Sep 2026 15:42:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/hugetlb: preserve mremap address delta when skipping page tables To: Jaewook You , Muchun Song , Oscar Salvador Cc: Andrew Morton , Johan Hovold , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260911182408.75821-1-jaewook376@gmail.com> <20260914132352.472-1-jaewook376@gmail.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: <20260914132352.472-1-jaewook376@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 0E8591C000B X-Stat-Signature: tioypxfc9cxu18moa8fwgfynqjayk1kh X-Rspamd-Server: rspam01 X-HE-Tag: 1789393366-897014 X-HE-Meta: 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 TZcxyeRw +bX/q65NOzfwcTPwke9+zIi8mf/nF/8LJbllWoYvHtzZzj0Ki6OZ65fV4ZFDEjNogBLWsN7sILMTKwyA5kIoehiMtZRjzBJYKtIT62zFMwuSLKoN5C0WMYJLC/jr6KTgqSDCeM8L6vgKl6OHcU/pQGXauVG35tnq4X4xlgJE6OdtbppjXCZ+TytFMwV6FQ1in+3x3GdSH3DPF81bU9uPll/E3txkzwUAjvfJu36jCXydiMjxkTXgWbmJN27aV79Trhppm8hLxcE9XGnM4+I0/mdoXbYnAyzAJON086L/GLhNbPa/xzKSo3woYKA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/14/26 15:23, Jaewook You wrote: > move_hugetlb_page_tables() optimizes mremap() by advancing to the last > entry in the page table when the source page table does not exist, either > initially or after unsharing a PMD table. The common loop increment then > steps to the first entry in the next page table. > > However, the code advances both the source and destination addresses to > the last entries in their respective page tables, which is wrong. The > destination address must be advanced only by the same amount as the source > address. > > If the source and destination offsets within their page tables differ, the > destination address can be advanced too far, causing follow-up issues. Fix > this by advancing the destination address by the source advance distance. > > With a reproducer, we were able to trigger a kernel panic on x86-64. With > this fix in place, we can no longer reproduce the issue. > > Fixes: e95a9851787b ("hugetlb: skip to end of PT page mapping when pte not present") > Fixes: 4ddb4d91b82f ("hugetlb: do not update address in huge_pmd_unshare") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Jaewook You > --- > Changes in v3: > - Clarify that the optimization advances to the last entry in the current > page table before the common loop increment steps to the next entry. > - Rename remaining_size to offset_to_last_entry as suggested by David. > > v2: https://lore.kernel.org/20260911182408.75821-1-jaewook376@gmail.com/ > v2 does not exist publicly ;) This would have been better send as a v1 upstream (I mentioned this in private but you might have missed it). > mm/hugetlb.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 4f6f58bf3db6c..5749f6270fb1f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5161,18 +5161,21 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, > hugetlb_vma_lock_write(vma); > i_mmap_lock_write(mapping); > for (; old_addr < old_end; old_addr += sz, new_addr += sz) { > + const unsigned long offset_to_last_entry = > + (old_addr | last_addr_mask) - old_addr; > + > src_pte = hugetlb_walk(vma, old_addr, sz); > if (!src_pte) { > - old_addr |= last_addr_mask; > - new_addr |= last_addr_mask; > + old_addr += offset_to_last_entry; > + new_addr += offset_to_last_entry; > continue; > } > if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) > continue; > > if (huge_pmd_unshare(&tlb, vma, old_addr, src_pte)) { > - old_addr |= last_addr_mask; > - new_addr |= last_addr_mask; > + old_addr += offset_to_last_entry; > + new_addr += offset_to_last_entry; > continue; As Oscar expressed, he might prefer some comment about the situation. But maybe that can be deferred to some proper cleanups here. Acked-by: David Hildenbrand (Arm) -- Cheers, David