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(p200300cbc70dfb00d3ed5f441b2d12af.dip0.t-ipconnect.de. [2003:cb:c70d:fb00:d3ed:5f44:1b2d:12af]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43995391824sm21752235e9.23.2025.02.18.09.25.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Feb 2025 09:25:36 -0800 (PST) Message-ID: Date: Tue, 18 Feb 2025 18:25:35 +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 Cc: Vlastimil Babka , 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> <37b606be-f1ef-4abf-83ff-c1f34567568e@redhat.com> <0db666da-10d3-4b2c-9b33-781fb265343f@redhat.com> <62c0ba1c-7724-4033-b1de-d62a59751ca5@lucifer.local> <6eb33b5d-3040-4637-b627-48f8f78e4e28@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: <6eb33b5d-3040-4637-b627-48f8f78e4e28@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 1mqj7N15cFxl0OJVZxK37DmhEfffKczWou1CmJfec1A_1739899537 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: A92F016000D X-Stat-Signature: iyu8dmtm7affwab55pwcik51n1hs3db1 X-HE-Tag: 1739899540-314232 X-HE-Meta: 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 zWInaALc 3PIk1ee7ZgumbYZcaY74X7lyWUs2FdzTfw3yAQK6IXX80HggCCLbjGiqrh6b6HuAjMdz1Vb2PCXHruMdk/wO2tsLeNe5ngD6Ob6RjI8D2w4sgmmHPMY2/masaNZa3BXQebv7lr5pUE2aYfAJ7sncV7tnTTlVhzMDbCrb3PtwmU6ned71VQFB/hWTIEoiXPLHtA4PULYd8ezaxLMtlA6mAChhWfLfXGTj3Y6ju/7WkFsofx2QUuX2INsSc6bvH+5G9cSRQB1OIgYyZmRFuvmil3xtT8Y9ZhPJFSfWbDO9MJ4LivF3xtBBYBCyr1ibaOpiXd1gVKKqjiG7Kj+er2UA4RHVYW510oR80UIJh2NQoVSnCvpU1m7pAdd8Ad87vT41+i2+Sr2fZKCVGrknys85bjhawifd/T6IboADIb7CTkAh2wlzwka/SAHQmxy+n+bH8VYROBoPL8ro86ejInLMDjp4zEjauyGzGmaXKIRaqMFxAfNM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000128, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> >> QEMU, for example, will issue an mlockall(MCL_CURRENT | MCL_FUTURE); when >> requested to then exit(); if it fails. > > Hm under what circumstances? I use qemu extensively to test this stuff with > no issues. Unless you mean it's using it in the 'host' code somehow. -overcommit mem-lock=on or (legacy) -realtime mlock=on I think. [...] >>> >>> It fails because it tries to 'touch' the memory, but 'touching' guard >>> region memory causes a segfault. This kind of breaks the idea of >>> mlock()'ing guard regions. >>> >>> I think adding workarounds to make this possible in any way is not really >>> worth it (and would probably be pretty gross). >>> >>> We already document that 'mlock()ing lightweight guard regions will fail' >>> as per man page so this is all in line with that. >> >> Right, and I claim that supporting VM_LOCKONFAULT might likely be as easy as >> allowing install/remove of guard regions when that flag is set. > > We already allow this flag! VM_LOCKED and VM_HUGETLB are the only flags we > disallow. See mlock2(); SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags) { vm_flags_t vm_flags = VM_LOCKED; if (flags & ~MLOCK_ONFAULT) return -EINVAL; if (flags & MLOCK_ONFAULT) vm_flags |= VM_LOCKONFAULT; return do_mlock(start, len, vm_flags); } VM_LOCKONFAULT always as VM_LOCKED set as well. -- Cheers, David / dhildenb