From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6629C26AA81 for ; Tue, 18 Feb 2025 14:35:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739889334; cv=none; b=ICZRL0OgQ0xi6lDWuvdqTCYT+u2FHmsBkrY69aSVsgM5pirA0N/XjI8PW+tszerm3TdZ4YxfF1YmYM1R0g1CiAmEgnprPjK4P4cOa90BDdJa6Pb/WJYJBNt5hXZRf+BUWZXYKWxUYnN5sJvZ5KBfFmh0UmVPe8jA4FpwUJunQaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739889334; c=relaxed/simple; bh=BZJVcic6DcAWJNzoMClc6kls9c2veIURLxuU379/2dA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GHl9D3+v3nWzthZiTwWFonv6SqL9/l7ehfg0nW0RAMs+kxPjKCRD/Nf+hunTnpnPg8IO4FwJ3B/XLoEZv1FZCcR9cXO7mKTG+Vm5tmDwRhX6R45HT55ik9v/619pGviUy1SDVxAI4xbe7c//hrhmEojt4NByxsrhgITEngcST/o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=UnJPg4RK; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UnJPg4RK" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739889331; 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=UnJPg4RKYEguAWeWuTq5XbhYuavWnLM8gCpjlAojSB/2+wCVFjPDyvbi/XzTopgSZ8mHlL aBhjTVJ8z348Zi9lxUluSskzgFCW0GVEQIrz33DM79P9HKJ2caQywRwdTv4RxcxC4eaMzO y/d0SlQ7tkOBry6WBYudVU9Kf96kbzc= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-682-xHT46FRcPauN0jRJd54MBA-1; Tue, 18 Feb 2025 09:35:29 -0500 X-MC-Unique: xHT46FRcPauN0jRJd54MBA-1 X-Mimecast-MFC-AGG-ID: xHT46FRcPauN0jRJd54MBA_1739889323 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-38f255d44acso1895938f8f.0 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=RbEakIIqkC841VdtntXLs3KRVP3wdSZJIMl0hYuOFJmRC/G2HChjDTulz8bojy2FP8 YkeCxjLJIocQnRROywBf5b2ldct6VYFX8yoPzgGreH1ZSEkMRgS6d+k/VXhnpZAVxRbR RvQt01m7+PUPp6ee5X+TLcdxyPlmXR1sr3czfJBtPbL6XxrCwCOll6bGg52iP9843zzp a0/rzZk9zLoaaTrYfnOPRJKqYuhnhB5m+G9XYq9e3WQQTida6o2vNAxb5lmNgor+Rk2X xRfOvvxHU4gK0QqFa89PN5FyctzFMUZvCqwn8SICxy0Zsltf8zp9noeqZ58eVWDL1mcJ /UjQ== X-Forwarded-Encrypted: i=1; AJvYcCVBr2lQj/YlMrSFy1I3yXL0cUVsrjhr2eQ02YaEuYSbeeipaavTVDOPjKQNOKWq6EhbIHb6hKRNEDhO0y/TnTY=@vger.kernel.org X-Gm-Message-State: AOJu0Yx8h4nKUF7Ov0fet1NNftT17V8qWnH2rmjX9UDkUpWApuxcrju1 sqSWJ9SYJDN4PRgSexjqxhd1PgASMynipJmVSfIapb6hHuiisX7YSTVsM1YFPHVG7ugij7YHLBz LJdF8AtREGr0OQ7YxQtqzJQMKoxBeENO0cP7x+bUcK0JB/6IcEM1CtAEfFoNpH+q8SA== X-Gm-Gg: ASbGnctvqYwHm4JFlyHsycFPJmx+VJptoSgnWSI5TPmI3wZjXA+aXnCMfx8Unkfxry1 IBq8y9W3Jxj0KoHt7mu2pcmJTB6nTdckHc+K95eFGnvnm3lvuVO89fsm3PTC6QeHBx5SsLcakLV T8KKr1V8pT90WrfVmIgFK3saIW2rq5z4zVv+tdDr7lt3QTMDSR7YoX0MuqTE+Fwdrxx+F3G6Jlx k4Af3Rydeo+ck0K0u2AWagX5Pww3Z5n5o0eiYsJ+D4kyne6BxG/xQUBpmclU0swkc5mYQzy8dda MTji2VZFgJhVhu3MjiuQuQ9X6JFvWFB78dl1Ti0VF+Xp3S2JaZVPEZf90Opja8eKseLBB6a8Lti uk/t4hp4x47d2h/l+HRqMz3aWzROi0CrM X-Received: by 2002:a5d:64c2:0:b0:38f:452f:9f89 with SMTP id ffacd0b85a97d-38f452fa26cmr7672911f8f.50.1739889322681; 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 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 Content-Language: en-US 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> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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