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b=HERcRnQJIVyzlX4GI8tM0lL03oWq6Sz2rY4lAo4NLLA6lhiufVUqyR/K6xYb4lWh+ KPX2LQsSl1L21PnwjtEVOdkxH5SAJuQkBC9VQNEjqGTffPWOcXNjdxxy1ammKXKoDO HedN1LPRIWc14gfv7Z6FeiLPBSpOdJBaY7T49JRGyvctiEJT9N+GK0JTU7MoK4QHTe qZG/GYKlq0bF4vwmnhkhTIQ/KYfc/F0IRSjLaJlkJNxBerb1GdFWNp00VYaRAkG4iE e1fptp4O3nI+9X1DfuD4bzLTeCHeslxUkd2jID6OK71TkeTB0XAQqjxJi48DnCZ6B7 DQqStQvtjhtqg== Message-ID: Date: Thu, 23 Apr 2026 15:04:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: honour FOLL_PIN in NOMMU __get_user_pages_locked() To: Greg Kroah-Hartman Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu References: <2026042334-acutely-unadorned-e05c@gregkh> <2026042314-traffic-riverbank-d9a1@gregkh> 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: <2026042314-traffic-riverbank-d9a1@gregkh> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: ABC44C0018 X-Rspamd-Server: rspam07 X-Stat-Signature: znrobe99n6qyy4wka4iqsj7xcujzqbbr X-Rspam-User: X-HE-Tag: 1776949501-602870 X-HE-Meta: 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 ZEUYQPvy cQzukmoy0rNmNW/cF2Qekan30/F688F3FhafuGvpulVcMBk2fLIlCmsMzasj2fISF608IpaM2BMG9aFrxXNyrWqch13pskl+kK3iqBaPRT8veTJCL1Daodl1QGpZRRPLPCtay4Y8H6JJ5ovFGdh65CcyXXkp9rsVgifyeHhKIH++UACJIdTGXZUS9AnB+JgfWjuvaNb6PA0Mvjla6bO+BNqvgHYC7rQLWjYOqBYVZXnPCEo25O8YcyTzMv4sE3RNpEntKtyYnoHzJwszCPa5ibIsHgKGUwrE/4bT7Mi071EHN8P96WiltWx7biEA5QwUhlq47qx221TqWyrUQjhPKEI38pQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> It just follows what we do everywhere else (e.g., follow_page_pte()). >> >> >>> + if (try_grab_folio(page_folio(pages[i]), 1, >>> + foll_flags)) { >>> + pages[i] = NULL; >>> + break; >>> + } >>> + } >> >> If it fails on the first iteration, we return -EFAULT instead of -ENOMEM. >> >> I know, I know, nobody cares. But if we touch it, we might just want to return >> the error we get from try_grab_folio(). > > So just abort here and return it? No, that will not work, there's a > lock we would jump around. How about something like this horrid thing, > adding back in the relevant unlikely() to match the other calls like > this: > > > diff --git a/mm/gup.c b/mm/gup.c > index ad9ded39609c..8fa5b37be8b7 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1983,6 +1983,7 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, > struct vm_area_struct *vma; > bool must_unlock = false; > vm_flags_t vm_flags; > + int ret; > long i; > > if (!nr_pages) > @@ -2019,8 +2020,15 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, > > if (pages) { > pages[i] = virt_to_page((void *)start); > - if (pages[i]) > - get_page(pages[i]); > + if (pages[i]) { > + ret = try_grab_folio(page_folio(pages[i]), 1, > + foll_flags); > + if (unlikely(ret)) { > + pages[i] = NULL; > + i = ret; > + break; So, we have to report the old i in case of an error. Assuming we want to also return -EFAULT on !pages[i] -- which i think we want, maybe the following (uncompiled and untested)? diff --git a/mm/gup.c b/mm/gup.c index ad9ded39609c..d00ff8d988fa 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1983,6 +1983,7 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, struct vm_area_struct *vma; bool must_unlock = false; vm_flags_t vm_flags; + int ret, err = -EFAULT; long i; if (!nr_pages) @@ -2019,8 +2020,14 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, if (pages) { pages[i] = virt_to_page((void *)start); - if (pages[i]) - get_page(pages[i]); + if (!pages[i]) + break; + ret = try_grab_folio(page_folio(pages[i]), 1, foll_flags); + if (ret) { + pages[i] = NULL; + err = ret; + break + } } start = (start + PAGE_SIZE) & PAGE_MASK; @@ -2031,7 +2038,7 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, *locked = 0; } - return i ? : -EFAULT; + return i ? : err; } #endif /* !CONFIG_MMU */ -- Cheers, David