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b=NAoHBUUC6iTOhnfEiRIL2ybzUIvjYJUlufJ6P2HXRugjhUvN0oxbF1Rz1J2+UVesd MSwhOvljnoikab8xv4GX4VgZJF3oY+jtQfYnKrlwYz/QhLJpTraFTE/LeyKhiHGpn9 xNzwctdLeHSap4lro0YBpoKyHLYc5FumKwa1e4HDWvhGykBEURMyMj6ySXwOEFY7wP idWqFcZgUE01OaMdEebblpkci77+WDc4G4qjLUh9nlqyebO5HzerVaHmIkBOd8NRK4 sKqJlmoX4ZelnHyyToErLTLBswdG823/SOgoLLThHRV8K4ZmOWwM3dUWWpOTewDYe4 sdSuyGymWGzVQ== Message-ID: <664b3576-05a9-4c49-99c6-ba0928b25300@kernel.org> Date: Fri, 11 Sep 2026 20:01:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: consolidate compound folio handling To: Hui Su , Andrew Morton Cc: Matthew Brost , Balbir Singh , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260911061348.2869524-1-sh_def@163.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: <20260911061348.2869524-1-sh_def@163.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: gnjan3r1dno3wa7qmnqcn1ia6rygxsh4 X-Rspam-User: X-Rspamd-Queue-Id: 2C39580004 X-Rspamd-Server: rspam03 X-HE-Tag: 1789149714-492088 X-HE-Meta: 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 NnrslZmy TU4t27fo1SsPgKeXZemndgSsDsH269xiiWl8PRYeed2JkC9wo6NXDBkiudppN9T0gD3uwM1F7tqAX8HQm49crQVLG6+Zsq3yF8P9WFNDxxW2OBGl0QVQjOgMfsq6JU9xMGqjJxfWntOhQTx2FAo9M2PeENjaXhDZvuUpCyVfT+aFdPjO55ohqFriCwipUhb9PzkZyUGMlMMGs7/Ms5iRDhnrMlRybhecer+F7q2MxafYe6KyBi9AT2eiTvgy/Xldi8WqtbIoy2z8PfFRnj8QvkPsTrQ46BgiDySg5xy4Gv7Dh3Gcdn+Cf+xCyNlegsoKBBVajhrXEQ5Sz0Opzs76poRRKiJvLRcqtnscW+vN9djra16Srgvr4vng9ErGu/azR2KBBcmIxD4Q5mIz/YEf2zZw9B0sKxV2IJcp4M8Bc8ux4bBs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/11/26 08:13, Hui Su wrote: > Commit dc41e961a269 ("mm/migrate_device: avoid out-of-bounds writes for > compound folios") added handling for compound folios that do not fit in > the remaining PFN array. > > migrate_device_range() and migrate_device_pfns() duplicate the logic for > locking device PFNs, encoding compound folios, and handling this boundary > condition. > > A compound folio cannot be represented partially for migration. Warn when > one does not fit in the remaining PFN array, while retaining the existing > defensive handling: release any lock and reference acquired for the > current folio, clear the remaining entries, and stop collecting. > > Move the shared collection and encoding logic into a helper so both > interfaces handle compound folios consistently. Also use memset() for > the compound-folio tail entries instead of open-coding the clearing loop. > > Document that an encountered compound folio must fit entirely in the > remaining range or PFN array. > > Link: https://lore.kernel.org/r/c99ca53a-73ef-4a0c-8738-eba1cc89bea2@kernel.org > Suggested-by: David Hildenbrand > Signed-off-by: Hui Su > --- > Tested on x86_64 with KASAN enabled: > > - Built mm/migrate_device.o and the kernel successfully. > - Ran the HMM migrate_anon_huge_zero selftest; the private-device case > passed. > - No KASAN report or truncated compound-folio WARN was observed. > > mm/migrate_device.c | 90 ++++++++++++++++++++++++--------------------- > 1 file changed, 49 insertions(+), 41 deletions(-) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 009bfa8b212d..c57eadea6565 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -1392,6 +1392,39 @@ static unsigned long migrate_device_pfn_lock(unsigned long pfn) > return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; > } > > +/* > + * Collect a device folio into the page-granular PFN array. > + * > + * Return the number of entries consumed, or 0 if the folio does not fit in > + * the remaining array. > + */ > +static unsigned int migrate_device_collect_folio(unsigned long *src_pfn, > + unsigned long pfn, > + unsigned long remaining) Two tab indent please. > +{ > + struct folio *folio = page_folio(pfn_to_page(pfn)); > + unsigned int nr; > + > + *src_pfn = migrate_device_pfn_lock(pfn); > + nr = folio_nr_pages(folio); > + > + if (WARN_ON_ONCE(nr > remaining)) { Just to be sure: there is no way we can currently validly trigger this, right? > + if (*src_pfn & MIGRATE_PFN_MIGRATE) { > + folio_unlock(folio); > + folio_put(folio); > + } > + memset(src_pfn, 0, remaining * sizeof(*src_pfn)); > + return 0; > + } > + > + if (nr > 1) { > + *src_pfn |= MIGRATE_PFN_COMPOUND; > + memset(src_pfn + 1, 0, (nr - 1) * sizeof(*src_pfn)); > + } > + > + return nr; > +} Looks much cleaner. -- Cheers, David