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b=WCEWqKKRcUw+sjbMY4GB6hIhqhRig1T9LBpWmxd+nA8f2RNcGBllNRagKqI5FzPkN 26WsO52bPsw5CHqjgtS4Rb3u2xUKya8vRxfVeFNKd2KLSLATsgfDBq4hpeNNIGXjZ8 2PO/vCswnxE0EQxQfrGL6LXYvtSayT9AeTQQOonJB5Ru/dqN2pcozNQcOwxcSJKQf2 GNvCRoso9B+/d6WwdVo4BS3ASXlLDzKauJCdFBiNLDBYCqY52n0jXnZLa+JiGGt0TQ GkErbG4t1NjoO/5a6oA4L8mPV3eO5mJDGDKtOE4Ufpkawu0K1TjSQmla59Tw4OqsG9 jEniXbBkz1QTA== Message-ID: <9eea2afb-8c35-47eb-b1de-6a08503c9679@kernel.org> Date: Fri, 8 May 2026 14:27:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/khugepaged: fix spurious -EINVAL from sub-PMD MADV_COLLAPSE range To: Chen Wandun , akpm@linux-foundation.org, ljs@kernel.org, shuah@kernel.org, zokeefe@google.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20260507070558.3064142-1-chenwandun@lixiang.com> <20260507070558.3064142-2-chenwandun@lixiang.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: <20260507070558.3064142-2-chenwandun@lixiang.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B731B1C0008 X-Stat-Signature: ns8xj1zh4a9pzxhtnix6ekh1dn1rdocz X-Rspam-User: X-HE-Tag: 1778243262-803139 X-HE-Meta: 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 E9fynIDk eYgKF65OZPjjnnAVQW3gob+YB4wLclL8TgHjOqc4b5Hz0/+nyVm91GdvgMsZPW9uynMT8aqLUM41e4tRK85bYvR97ho2ofSYwXK5QK8esJY1ccLrwNgqtR3647/YaaXjTk6CW9rRZV98VvK8pkMFHNz948ijxPeJEcSnMgauStn2FRHAje+aqatKGq1qDtz0+ZZynRF/QINcQyQGCSzjElz7j7obvZ2LaoBcbByv7jSYfuOAds0J8PTK0kSDyUvL78WUsULoPkqnL/1nlpigFoTk9JnDToWhA8X0VmJOjMSXHslKBURYoPBtk2zlBYuMcsISo/YIu4X0p2H9vh5qDk5KuOea4B5ATa+iQoT0i6jPkIBE8drrj9p44WHqpyYWAar/w Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/7/26 09:05, Chen Wandun wrote: > madvise_collapse() computes the THP-aligned window: > > hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK /* round up */ > hend = end & HPAGE_PMD_MASK /* round down */ > > Previously this was done after kmalloc_obj(), so problem arose when > the range contained no complete PMD-aligned window (hstart >= hend). > > When hstart > hend, (hend - hstart) wraps unsigned to a huge value, the > final comparison fails and -EINVAL is returned instead of 0. Consider > two single-page calls on a 2 MiB-aligned address: > > /* hstart == hend == aligned -> 0 == 0 -> returns 0 */ > madvise(aligned, PAGE_SIZE, MADV_COLLAPSE); > > /* hstart = aligned + 2MiB, hend = aligned > * (hend - hstart) wraps unsigned -> returns -EINVAL */ > madvise(aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); > > Both calls cover less than one THP and collapse nothing; both should > return 0. Okay, so we talk about a "userspace is being stupid" scenario. > > In addition, kmalloc_obj(), mmgrab() and lru_add_drain_all() were all > called before discovering there was nothing to do, only for the code > to kfree() and return immediately after. Just a comment as you motivate here why this is suboptimal: we do not care about a "userspace is being stupid" scenario being fast. > > Fix both by computing hstart/hend after thp_vma_allowable_order() but > before kmalloc_obj(), and returning 0 early when hstart >= hend. > > Fixes: 7d8faaf15545 ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse") Fixes: is likely ok, but I don't think we want to treat this as a hotfix or CC stable. > Signed-off-by: Chen Wandun > --- > mm/khugepaged.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index b8452dbdb043..92473d93e837 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2836,6 +2836,12 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER)) > return -EINVAL; > > + hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; > + hend = end & HPAGE_PMD_MASK; > + > + if (hstart >= hend) > + return 0; > + > cc = kmalloc_obj(*cc); > if (!cc) > return -ENOMEM; > @@ -2845,9 +2851,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > mmgrab(mm); > lru_add_drain_all(); > > - hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; > - hend = end & HPAGE_PMD_MASK; > - > for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { > enum scan_result result = SCAN_FAIL; > In general, LGTM, but see for conflict: https://lore.kernel.org/all/20260409014323.2385982-1-ye.liu@linux.dev/ -- Cheers, David