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b=JooeV2AhyukQcKllXv3qlcIRIL/p8bVgh/uB0cuwFguDijyU3xwg6iKIygYOTss3a XjQbTLK5F3zbOFSiUEZ4L/9KpJWI380qKf5HL3Le4VEwxBsvNDyk3UQzx043e8JnLW WRrNmP6Y5sRm0d13vAt60HR3WHZODKU4pBzGmxrk9wvAzpOLmhA9hnwXUExJ38eIjK vCjk0qnuH0xJXnQqsTcF5+uxWOaX2bRO63+GkV7xTE5DC67XOgr42T67fg8cEsQ8yw PsATXEjzNxR51yYUsGzaK6nl8C4ntRTKH5NBFCjUbSU7EzGkU7gKDkdoBy9vEEenos R4kaN5fSKKRrQ== Message-ID: Date: Wed, 8 Jul 2026 10:43:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: avoid overflowing migrate_vma collection arrays To: Zi Yan , Andrew Morton , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Balbir Singh , Kefeng Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko References: <20260707-fix-array-overflow-in-migrate_vma_collect_pmd-v1-1-ce3ff4627653@nvidia.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: <20260707-fix-array-overflow-in-migrate_vma_collect_pmd-v1-1-ce3ff4627653@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BC7C680004 X-Stat-Signature: zx4ge3gj9u7qxero5k9bhjkd9uua5ggd X-HE-Tag: 1783500216-34767 X-HE-Meta: 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 Iq+A8Imq 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/8/26 03:50, Zi Yan wrote: > migrate_vma_collect_pmd() can drop pte lock to split a large folio and > restart. But the code does not handle restart properly when pmd becomes > huge or cleared. It can overflow migrate->dst and migrate->src arrays > during the hole or skip collection. Fix it by: > 1. avoiding migrate_vma_collect_huge_pmd() if some collection is done, > 2. skipping the rest of the range if pmd no longer points to a pte page > table. > > Fixes: a30b48bf1b244 ("mm/migrate_device: implement THP migration of zone device pages") > Reported-by: Sashiko > Closes: https://sashiko.dev/#/patchset/20260706111958.3649651-1-wangkefeng.wang@huawei.com > Assisted-by: Claude:claude-opus-4-8 > Signed-off-by: Zi Yan > --- > The issue is spot by Sashiko during a patch[1] review as a pre-existing one. > This patch has the minimal change. An alternative is to reset > migrate->cpages and migrate->npages and restart the whole range from the > beginning, but that also requires a restoration of no-longer-present PTEs. > > Link: https://lore.kernel.org/all/20260706111958.3649651-1-wangkefeng.wang@huawei.com/ [1] > --- > mm/migrate_device.c | 19 +++++++++++++++++-- > 1 file changed, 17 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 2fffeb1f99694..6ceb47ec1da24 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -257,7 +257,12 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > pte_t *ptep; > > again: > - if (pmd_trans_huge(*pmdp) || !pmd_present(*pmdp)) { > + /* > + * Only check pmd when addr is at start, namely no pte is collected. > + * It avoids collecting the same address range [start, addr) twice > + * and overflowing the collection arrays. > + */ > + if (addr == start && (pmd_trans_huge(*pmdp) || !pmd_present(*pmdp))) { > int ret = migrate_vma_collect_huge_pmd(pmdp, start, end, walk, fault_folio); > > if (ret == -EAGAIN) > @@ -267,8 +272,18 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > } > > ptep = pte_offset_map_lock(mm, pmdp, start, &ptl); > - if (!ptep) > + if (!ptep) { > + /* > + * Skip the rest if pmd becomes huge or cleared. Flush if any > + * pte is modified > + */ > + if (addr != start) { > + if (unmapped) > + flush_tlb_range(walk->vma, start, end); > + return migrate_vma_collect_skip(addr, end, walk); > + } > goto again; > + } > lazy_mmu_mode_enable(); > ptep += (addr - start) / PAGE_SIZE; It's hard to express which feelings reading migrate_vma_collect_pmd() gives me, haha :) In case we split ... couldn't we just undo what we already did, before doing the "goto again" ? -- Cheers, David