From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7DCE3C7EE2A for ; Fri, 27 Jun 2025 15:49:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1E3A16B00A8; Fri, 27 Jun 2025 11:49:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 16D076B00BB; Fri, 27 Jun 2025 11:49:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 00DB36B00BD; Fri, 27 Jun 2025 11:49:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id DD5486B00A8 for ; Fri, 27 Jun 2025 11:49:36 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id AB3C71CE042 for ; Fri, 27 Jun 2025 15:49:36 +0000 (UTC) X-FDA: 83601615552.09.48E96B9 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf13.hostedemail.com (Postfix) with ESMTP id 24B5520013 for ; Fri, 27 Jun 2025 15:49:33 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VwimZiQo; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1751039374; a=rsa-sha256; cv=none; b=0BDkQ9JhNyRYO3c/eizmC6xNqjgZgY6pTgc5Fv7BoA+uKQwTqwzgGZlOU178nznXfAIjKF I4MgRrOAlgNCxMex2Jz3u3RANh33E8NZY9gPGvbwDcPMKuRCvnX38EfD8yhHeuhanqlJqo Vdh25TGGGd8tnmEOlJGFYvEnvMbE2nw= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VwimZiQo; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1751039374; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=MWpQhfcMYiannUA+rJ5gOh1mNCZnzLMoO5gh2F8JmmM=; b=aa+sl0Z4kyQJHKEUGK8FfrbwDsflKeN2KFbb7SyHyX3ap0AAYlyy79QWFhgcYsrl6Uhpxc QxtVaSvZLSDJBoi/IPbbIIv4MFJjIqJMQdy6POchOSzVU559fluQQrvMKFX/CXgcZ7Eivb ChDP6wJOADfV189jKiqWekyz9N3Fsa4= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1751039373; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=MWpQhfcMYiannUA+rJ5gOh1mNCZnzLMoO5gh2F8JmmM=; b=VwimZiQo0Kp19uGnL33rMp1lfWE4Tvk+S7VOTmuFkUyBMxgiTFjNzjEbMKYPWfrHi6/RcN IDNUNPrCmnMLwJeMlvbtySFiJmZ/qYjiRXsbqvzpMYEz0TCLTbdgLoZbHBXgAQnnxOl08o DXC99YD8ii3ihqIpQR3AcDKdEDuxco8= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-400-PFNOo70JOeCnNUQ7z8Q73g-1; Fri, 27 Jun 2025 11:49:31 -0400 X-MC-Unique: PFNOo70JOeCnNUQ7z8Q73g-1 X-Mimecast-MFC-AGG-ID: PFNOo70JOeCnNUQ7z8Q73g_1751039370 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-4530c186394so173995e9.0 for ; Fri, 27 Jun 2025 08:49:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1751039370; x=1751644170; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=MWpQhfcMYiannUA+rJ5gOh1mNCZnzLMoO5gh2F8JmmM=; b=DpqjUP5Z85M+BHK3OtwVVUTPU7kZXJG3YgChveyplaJ/BnueM/vsPyEjwBHSOKi2Qj 9x1XDh45i/k7rhNcGl/Zdu3lnnBvXbhYw2gge4N112cERpVhGutnTbk91IeKsUffED9E +pUOGdLfUdZ+DhOaTYH7cQY7Jh5cP+g2D9zG18yjzhQCtb+rkB6BYgsHf/wkeYvznBMh piwLY1GSLKaV6Akxpklm/EX5HBwM0SUe0jwsUrsSS/FT9WL7I6VymDdAOcWA4L2QAuLc xVJQNqPTaYEP38oNjPvgCenK69V94wVMZFnIbnSAQKYQuuW4tgyqXzK/Jm7JnUzXze12 KUjA== X-Forwarded-Encrypted: i=1; AJvYcCVWqYgmZiBRGGiEhfz8VjgZ92UMbfu9D6vmAlBtXOVInzBCIiD4thPlQgJsTexQ2YS6Q10FUGTktA==@kvack.org X-Gm-Message-State: AOJu0YzTSuaXgL1yMNU9lZDJ6WQoI8s0yhhfpkTkJXdk/vjURtM7gL6z Bh970loGDEJpeXXTcFwevku87Zz9q6Yke86E4znSUUVibf/F0FiA+fHcQKzlPOMbz3ZiQ2pbFZI RmAhxv8/ioy2W3tGQjWZOkW+LstGu8Yxj5TIJr3cJ6pRbPWB/WbQMtkjIhy/RzfA= X-Gm-Gg: ASbGncu+poACaaLxZTJ1z9eIW2EKUNDasD+LGuLckw7r0AuTqYQFzu/qBjH30GOUP7c VYAtek7rJMjVc1DdhJ8ofohZBEQiNSKCObpAU9vTfByPaO6sHd4nXsPUxRBWPUNLl7XNzPXOpaC fWM/8XV0hKW55TlyUdoYABnqf0h+vjBQuQ4nAYe7IyUmW+RCKtNiVarqrMb0toe7XTpexwauVhZ mDizHrfk8exJPEtj2yXr/MSvJPnLQnsPR7aRg9LxGO6Y4z2u4XlKB8+VX2iFUJRG37CK0TNzzcl bwxtxI2F59dqvruKqPpgp7ri3sEwru7LptMEKLEEJQlkfvI2ntHZKs+bQtzsWLI1PPf8Lz7EwjI JssK4iYGZ7oTfgIWkMtbvfkvgOm3v1URCSY8cEasybdFSncevcQ== X-Received: by 2002:a05:600c:4e8b:b0:453:8a63:b484 with SMTP id 5b1f17b1804b1-4538ee75d5emr46069305e9.30.1751039369718; Fri, 27 Jun 2025 08:49:29 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFf34PqbJ8qzLhvpscXunFC56wXeCg2MQwLGMyj61jFGMywYScq+JOuap9GUf8ACPcIqst2ow== X-Received: by 2002:a05:600c:4e8b:b0:453:8a63:b484 with SMTP id 5b1f17b1804b1-4538ee75d5emr46068935e9.30.1751039369204; Fri, 27 Jun 2025 08:49:29 -0700 (PDT) Received: from ?IPV6:2003:d8:2f2d:5d00:f1a3:2f30:6575:9425? (p200300d82f2d5d00f1a32f3065759425.dip0.t-ipconnect.de. [2003:d8:2f2d:5d00:f1a3:2f30:6575:9425]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453923a22fbsm13811675e9.34.2025.06.27.08.49.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Jun 2025 08:49:28 -0700 (PDT) Message-ID: <790e550f-3d6e-4eb2-be3c-a5feaaac1ce0@redhat.com> Date: Fri, 27 Jun 2025 17:49:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] mm/rmap: fix potential out-of-bounds page table access during batched unmap To: Lance Yang , Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, huang.ying.caritas@gmail.com, zhengtangquan@oppo.com, riel@surriel.com, Liam.Howlett@oracle.com, vbabka@suse.cz, harry.yoo@oracle.com, mingzhe.yang@ly.com, stable@vger.kernel.org, Lance Yang References: <20250627062319.84936-1-lance.yang@linux.dev> <1d39b66e-4009-4143-a8fa-5d876bc1f7e7@linux.dev> <609409c7-91a8-4898-ab29-fa00eb36df02@redhat.com> <530101b3-34d2-49bb-9a12-c7036b0c0a69@linux.dev> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <530101b3-34d2-49bb-9a12-c7036b0c0a69@linux.dev> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: h0Kuo0G7V9us-NYH5rKCyj60vQlTWMKQEp1q8V7jCzA_1751039370 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: etnsneafaqja49oeboh463ztem7xkoje X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 24B5520013 X-Rspam-User: X-HE-Tag: 1751039373-761438 X-HE-Meta: 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 gMBDQJQF 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27.06.25 17:29, Lance Yang wrote: > > > On 2025/6/27 18:13, David Hildenbrand wrote: >> On 27.06.25 09:36, Barry Song wrote: >>> On Fri, Jun 27, 2025 at 7:15 PM Lance Yang wrote: >>>> >>>> >>>> >>>> On 2025/6/27 14:55, Barry Song wrote: >>>>> On Fri, Jun 27, 2025 at 6:52 PM Barry Song <21cnbao@gmail.com> wrote: >>>>>> >>>>>> On Fri, Jun 27, 2025 at 6:23 PM Lance Yang >>>>>> wrote: >>>>>>> >>>>>>> From: Lance Yang >>>>>>> >>>>>>> As pointed out by David[1], the batched unmap logic in >>>>>>> try_to_unmap_one() >>>>>>> can read past the end of a PTE table if a large folio is mapped >>>>>>> starting at >>>>>>> the last entry of that table. It would be quite rare in practice, as >>>>>>> MADV_FREE typically splits the large folio ;) >>>>>>> >>>>>>> So let's fix the potential out-of-bounds read by refactoring the >>>>>>> logic into >>>>>>> a new helper, folio_unmap_pte_batch(). >>>>>>> >>>>>>> The new helper now correctly calculates the safe number of pages >>>>>>> to scan by >>>>>>> limiting the operation to the boundaries of the current VMA and >>>>>>> the PTE >>>>>>> table. >>>>>>> >>>>>>> In addition, the "all-or-nothing" batching restriction is removed to >>>>>>> support partial batches. The reference counting is also cleaned up >>>>>>> to use >>>>>>> folio_put_refs(). >>>>>>> >>>>>>> [1] https://lore.kernel.org/linux-mm/ >>>>>>> a694398c-9f03-4737-81b9-7e49c857fcbe@redhat.com >>>>>>> >>>>>> >>>>>> What about ? >>>>>> >>>>>> As pointed out by David[1], the batched unmap logic in >>>>>> try_to_unmap_one() >>>>>> may read past the end of a PTE table when a large folio spans >>>>>> across two PMDs, >>>>>> particularly after being remapped with mremap(). This patch fixes the >>>>>> potential out-of-bounds access by capping the batch at vm_end and >>>>>> the PMD >>>>>> boundary. >>>>>> >>>>>> It also refactors the logic into a new helper, >>>>>> folio_unmap_pte_batch(), >>>>>> which supports batching between 1 and folio_nr_pages. This improves >>>>>> code >>>>>> clarity. Note that such cases are rare in practice, as MADV_FREE >>>>>> typically >>>>>> splits large folios. >>>>> >>>>> Sorry, I meant that MADV_FREE typically splits large folios if the >>>>> specified >>>>> range doesn't cover the entire folio. >>>> >>>> Hmm... I got it wrong as well :( It's the partial coverage that triggers >>>> the split. >>>> >>>> how about this revised version: >>>> >>>> As pointed out by David[1], the batched unmap logic in >>>> try_to_unmap_one() >>>> may read past the end of a PTE table when a large folio spans across two >>>> PMDs, particularly after being remapped with mremap(). This patch fixes >>>> the potential out-of-bounds access by capping the batch at vm_end and >>>> the >>>> PMD boundary. >>>> >>>> It also refactors the logic into a new helper, folio_unmap_pte_batch(), >>>> which supports batching between 1 and folio_nr_pages. This improves code >>>> clarity. Note that such boundary-straddling cases are rare in >>>> practice, as >>>> MADV_FREE will typically split a large folio if the advice range does >>>> not >>>> cover the entire folio. >>> >>> I assume the out-of-bounds access must be fixed, even though it is very >>> unlikely. It might occur after a large folio is marked with MADV_FREE and >>> then remapped to an unaligned address, potentially crossing two PTE >>> tables. >> >> Right. If it can be triggered from userspace, it doesn't matter how >> likely/common/whatever it is. It must be fixed. > > Agreed. It must be fixed regardless of how rare the scenario is ;) > >> >>> >>> A batch size between 2 and nr_pages - 1 is practically rare, as we >>> typically >>> split large folios when MADV_FREE does not cover the entire folio range. >>> Cases where a batch of size 2 or nr_pages - 1 occurs may only happen if a >>> large folio is partially unmapped after being marked MADV_FREE, which is >>> quite an unusual pattern in userspace. >> >> I think the point is rather "Simplify the code by not special-casing for >> completely mapped folios, there is no real reason why we cannot batch >> ranges that don't cover the complete folio.". > > Yeah. That makes the code cleaner and more generic, as there is no > strong reason to special-case for fully mapped folios ;) > > Based on that, I think we're on the same page now. I'd like to post > the following commit message for the next version: > > ``` > As pointed out by David[1], the batched unmap logic in try_to_unmap_one() > may read past the end of a PTE table when a large folio's PTE mappings > are not fully contained within a single page table. > > While this scenario might be rare, an issue triggerable from userspace must > be fixed regardless of its likelihood. This patch fixes the out-of-bounds > access by refactoring the logic into a new helper, folio_unmap_pte_batch(). > > The new helper correctly calculates the safe batch size by capping the > scan at both the VMA and PMD boundaries. To simplify the code, it also > supports partial batching (i.e., any number of pages from 1 up to the > calculated safe maximum), as there is no strong reason to special-case > for fully mapped folios. > ``` > > So, wdyt? Sounds good to me. -- Cheers, David / dhildenb