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 00EB5C021AA for ; Tue, 18 Feb 2025 14:35:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4911F280139; Tue, 18 Feb 2025 09:35:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 44063280138; Tue, 18 Feb 2025 09:35:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 292F7280139; Tue, 18 Feb 2025 09:35:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 07AD0280138 for ; Tue, 18 Feb 2025 09:35:36 -0500 (EST) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 11B411213F0 for ; Tue, 18 Feb 2025 14:35:32 +0000 (UTC) X-FDA: 83133313704.05.421BA8B Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf02.hostedemail.com (Postfix) with ESMTP id 40DFE80013 for ; Tue, 18 Feb 2025 14:35:28 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=a6cqrOY+; spf=pass (imf02.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1739889329; 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=2BBgcXRJrBgS4bqLk6IB+Bu0JRKwgATueMPPbzZjJrI=; b=3NCOGtl8ExuTQ8Nl187PU80BO8A98UJApu9bt1ka+TE+6ZNg8BlAo/EU1hEm3oRVb+NO+4 Hgfh1MMTh1/c5zjsIvBlIVmpsTVo5Ggy2b86qVXf46rz+f23HIsnnVBI93R+7JIpUVag0Z M4fdpgXMn8L8IWnf7Vr/HsQOJdM3i/o= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=a6cqrOY+; spf=pass (imf02.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1739889329; a=rsa-sha256; cv=none; b=AH/a0KLae2RpUQzfdWxGfSIvKgOCu2xkbZzFczNFbhys/IP3HW0UOLocdjZ7Ry8lzeYW0j NQ+NGF65h+OgSXtrkahqKh+6vV0ZAJj6cCe0BID1G0IztOQ0ztYOf9jbg1VKEl8GhVwBVR rzcgCNvt5vHj+rmKr1NUKOmw1UDvFQM= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739889328; 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=2BBgcXRJrBgS4bqLk6IB+Bu0JRKwgATueMPPbzZjJrI=; b=a6cqrOY+1sFxrdaTks7jqPdB/wPVWDm4tZtH8DabfKHa6ez3nkzZEHkIXcr10GLIMocVMN GeaFu0euNV1ZXHKUK6r0w8Xe42q/rEsxle6tDYxM0DiYzgPObS/DGScX36vUd1QDltwGWF tVOabhPqK7so8UMa8g1GF7+3ibWx7xQ= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-679-TtdLB-35PjOS0DJ1-gaDAg-1; Tue, 18 Feb 2025 09:35:24 -0500 X-MC-Unique: TtdLB-35PjOS0DJ1-gaDAg-1 X-Mimecast-MFC-AGG-ID: TtdLB-35PjOS0DJ1-gaDAg_1739889323 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-38f36fcf4b3so2044238f8f.1 for ; Tue, 18 Feb 2025 06:35:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739889323; x=1740494123; 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=2BBgcXRJrBgS4bqLk6IB+Bu0JRKwgATueMPPbzZjJrI=; b=HusglMrh8EtxLeWxTRUIZcchT/t8anUq6maLBAzi0YMyg3d8ew0sYQFRzFE5muoKnD cVY+NW/7GwLhzT7L2rB2/vh75XXd9RLT3+4nXNz2wbmF33Xkq/Hly1ozVqBylyr2C2g9 BUvwNQ+IO4AfR8Mz49ny62Gj3Rkp/YmU+y1pJ+ROSbw2BgkwyTnCPp1zBivLhnIwsTBq GeYC0TxKe4aJo3Pva+JpppQZnxDylIXdWRtMKF+GiYuECa4GcZwH49dwPNsbl2Aj23h7 njbLZm36zXIq5AkL2Sr2ejyxPoePy3h3owZVDDAWfdgSZxz5SjkFuE2ZU/2Vu7mxeLB6 57Uw== X-Forwarded-Encrypted: i=1; AJvYcCXyxXdArQKOcZ6VgdxDUvdEOh34vs+Z1hMZ/5UPcq8ufuOOeKe0Wo220Ju82SxQp0MZ7/1hG6YdrA==@kvack.org X-Gm-Message-State: AOJu0YywvEs6ubAoDnq+nziTgnaG/STROGDftXFK6cqms5fRV64AuXLH 3Y35GFivH8uQ+F9hkbh1TWmFDNZKDeOtN6VjGkuXtIfbmJawDOp6Ztcyc50srgqLfodkN2SbKvS 31BtixJyFb7wLBMbHFgn9BFKIPXQytc56pbrQ9zpR7Otr6UsgSseJBjoIyv8= X-Gm-Gg: ASbGncvWR1HiYRUDPDbf+/b2aTPy483RdN3kTGcT2V6dleRb/hDRaEcHPKm1xZem7ho c0g4VOz3hkDlNp1dKfnoRnmZJG4v5/bM3GjdJhTS1Qzz318fv0vHEstgbqNmD4Hog3YzqOqhysG RLxhD/joHLaHwwiEiOxeKJ2/iEMJPdAEzUtW+8EP91nINpZ+AgYT1mW9LglIYWKFE9Pmj6XKec7 aXIs5z1JnwHEeAx5NA9uDfU7LLNZ7+qgs527zCzL5D+fXTtxScwN0oLE1LPW00p83LHFOyx7MW3 ldfbUuYaLFnQWej8ozXjT7rX2nQfYefIWNweFHvD/9o4rGYR8DK0n5iX/mHzxlpoKtDe2qDr53h lijsTVESd4kB3Dl+qY3P7TDcf+OOk5Q7s X-Received: by 2002:a5d:64c2:0:b0:38f:452f:9f89 with SMTP id ffacd0b85a97d-38f452fa26cmr7672909f8f.50.1739889322680; Tue, 18 Feb 2025 06:35:22 -0800 (PST) X-Google-Smtp-Source: AGHT+IECohohAOqe4JhXJYwDCfx/E8JPPIGDkcaVLHfskcflyFiuSiy2JNsExexnSee00wptapNfFA== X-Received: by 2002:a5d:64c2:0:b0:38f:452f:9f89 with SMTP id ffacd0b85a97d-38f452fa26cmr7672875f8f.50.1739889322290; Tue, 18 Feb 2025 06:35:22 -0800 (PST) Received: from ?IPV6:2003:cb:c70d:fb00:d3ed:5f44:1b2d:12af? (p200300cbc70dfb00d3ed5f441b2d12af.dip0.t-ipconnect.de. [2003:cb:c70d:fb00:d3ed:5f44:1b2d:12af]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259d5655sm15145789f8f.77.2025.02.18.06.35.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Feb 2025 06:35:21 -0800 (PST) Message-ID: <37b606be-f1ef-4abf-83ff-c1f34567568e@redhat.com> Date: Tue, 18 Feb 2025 15:35:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/4] mm: permit guard regions for file-backed/shmem mappings To: Lorenzo Stoakes , Vlastimil Babka Cc: Andrew Morton , Suren Baghdasaryan , "Liam R . Howlett" , Matthew Wilcox , "Paul E . McKenney" , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shuah Khan , linux-kselftest@vger.kernel.org, linux-api@vger.kernel.org, John Hubbard , Juan Yescas , Kalesh Singh References: <8d643393-ddc0-490d-8fad-ad0b2720afb1@lucifer.local> 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: <8d643393-ddc0-490d-8fad-ad0b2720afb1@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: duYAt8qUxf1Rssrd6pYj_hLmiGJfcQNNAnfEUpKr5m8_1739889323 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 40DFE80013 X-Stat-Signature: uzfnqijm8r7ekxbhp5ybjw9bpzjfqakq X-Rspam-User: X-HE-Tag: 1739889328-982139 X-HE-Meta: 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 tKoXRnAs LzddxOSDc0oIeXIjkfA3uu4w+Gl/CcMz+EQOId2foGqN6V+Oij9W3ecVo8cdM4fZwNTvvBzZLWal6BD9xv2vOT8zTffaZBjb+W/wJa2aSZz9oWBOnuLkyuCELi5eJFjovqSRT5gxGA0g1J6l2HJ5BVVntcw5LRvjQhDZVH2w3DFqQH14M5/jifd5GvLmB2E/+yi16opnSXr48g1KjcVHUJzLgpen8xg3TjarxSuNYGClZu6Bjndv6a7tIbyfEhiuytbG5Z1IZr7zOQQWoUgcQGZTyl1002/hqhHslONplaq+o8T1byG9afaJ92AMpAs2wfLNM9JKMxD8mmM4ZpuRXCelqDGTFx2LCHAaTJ+iQBU+9bZqx+WlZCBnJYA3YLb3qZgWuJLJAKlRihvoYaateM5RNGVXqRXqKrcFiB1Rd0EkkKZl+HkuG/tQ/4PO9p1GG1b/nGI70a2YX5GU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000014, 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 18.02.25 14:05, Lorenzo Stoakes wrote: > On Tue, Feb 18, 2025 at 01:12:05PM +0100, Vlastimil Babka wrote: >> On 2/13/25 19:16, Lorenzo Stoakes wrote: >>> The guard regions feature was initially implemented to support anonymous >>> mappings only, excluding shmem. >>> >>> This was done such as to introduce the feature carefully and incrementally >>> and to be conservative when considering the various caveats and corner >>> cases that are applicable to file-backed mappings but not to anonymous >>> ones. >>> >>> Now this feature has landed in 6.13, it is time to revisit this and to >>> extend this functionality to file-backed and shmem mappings. >>> >>> In order to make this maximally useful, and since one may map file-backed >>> mappings read-only (for instance ELF images), we also remove the >>> restriction on read-only mappings and permit the establishment of guard >>> regions in any non-hugetlb, non-mlock()'d mapping. >> >> Do you plan to address mlock later too? I guess somebody might find use for >> those. Is there some fundamental issue or just that we need to define some >> good semantics for corner cases? (i.e. if pages are already populated in the >> mlocked area, discarding them by replacing with guard pte's goes against >> that, so do we allow it or not?). > > Yeah that's the fundamental issue with mlock, it does not interact with the > zapping part of MADV_GUARD_INSTALL, and that is why we disallow it (but not so > for MADV_GUARD_REMOVE, as if a VMA that contains guard regions is locked > _afterwards_ there will be no zapping). > > We could potentially expose an equivalent, as there are for other flags, a > _LOCKED variant of the madvise() flag, like MADV_GUARD_INSTALL_LOCKED to make > this explicit. > > That is probably the most sensible option, if there is a need for this! mlock is weird, because it assumes that memory will be faulted in in the whole VMA. You'd likely have to populate + mlock the page when removing the guard. Also not sure what happens if one does an mlock()/mlockall() after already installing PTE markers. __mm_populate() would skip whole VMAs in case populate_vma_page_range() fails. And I would assume populate_vma_page_range() fails on the first guard when it triggers a page fault. OTOH, supporting the mlock-on-fault thingy should be easy. That's precisely where MADV_DONTNEED_LOCKED originates from: commit 9457056ac426e5ed0671356509c8dcce69f8dee0 Author: Johannes Weiner Date: Thu Mar 24 18:14:12 2022 -0700 mm: madvise: MADV_DONTNEED_LOCKED MADV_DONTNEED historically rejects mlocked ranges, but with MLOCK_ONFAULT and MCL_ONFAULT allowing to mlock without populating, there are valid use cases for depopulating locked ranges as well. Adding support for that would be indeed nice. -- Cheers, David / dhildenb