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(p200300d82f38ca00ca3a83da653e0234.dip0.t-ipconnect.de. [2003:d8:2f38:ca00:ca3a:83da:653e:234]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45617f18d99sm44212725e9.8.2025.07.14.08.41.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Jul 2025 08:41:46 -0700 (PDT) Message-ID: <184d7f4b-6ffd-4047-b245-aec32ebda9d6@redhat.com> Date: Mon, 14 Jul 2025 17:41:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] mm/mseal: move madvise() logic to mm/madvise.c To: Pedro Falcato Cc: Lorenzo Stoakes , Andrew Morton , "Liam R . Howlett" , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jeff Xu References: <5d932ec1f9d0ea115aac65067e4cb8241a06e791.1752497324.git.lorenzo.stoakes@oracle.com> <5e21df9f-7f75-412b-a173-fe6da49952e5@redhat.com> <0925c64b-c721-4dc5-913a-c43a94dc64a3@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: -jhS145hZORafPQcWd29Qk4HXmZSqQ6219IoUytjshM_1752507708 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: rspam05 X-Rspamd-Queue-Id: 278DE140012 X-Stat-Signature: yxwbkbqe4bhiw7nksx3f7whr1ey7bsaz X-HE-Tag: 1752507712-127735 X-HE-Meta: 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 lolaEIlW yUsEThgtHtUh6oIz7QnqVLmsg1dqtziuAwBwPX2WFLmf+t0OKBTo7b9D4Yvezy1QJCKdzERWgDIT8M2e3OV3km12C8QJou6NuSQdSY7aBf0gwomiY2B1f1RbcIGa/u76lqmNuA66lV0aChcQYCO6nwu1Q/jTCiRH6sEK3mtz5dTDYjcI8YQEIz1+06QIIsZtTmvCTpaA/In284DXDiX/WkLfMLYjfbOVFrylxN4nvmITea7kL5ed4l80ujaddc46DGZQEWoMFHNT86xvBJmZjtHaqScdfo0Y0USOtV78dmNOmdPsedhEgNby38Mswka/FNdRZUZ1HowXs3sEuhHM+2wDdoll8gIO0B3WPh81tcPc3EAePx9lQj2eSLW6neld6YQnD8uimx7jxaGosxo8S/sZ78Jt1pg20fZBDmCgaXIDRlv7sUnj5lsFtYR3vvtJDkN3nQJP1eubwvCfCUXtcf3pItA== 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 14.07.25 17:31, Pedro Falcato wrote: > On Mon, Jul 14, 2025 at 05:03:03PM +0200, David Hildenbrand wrote: >> [...] >> >> But now I wonder, why is it okay to discard anon pages in a MAP_PRIVATE file >> mapping? > > IIRC this was originally suggested by Linus, on one of the versions introducing > mseal. But the gist is that discarding pages is okay if you could already zero > them manually, using e.g memset. Hence the writeability checks. What you can do is a) mmap(PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, ...) b) modify content (write, whatever) c) mprotect(PROT_READ) d) mseal() But then still do madvise(MADV_DONTNEED) to discard. There is no writability anymore. (Just a note that, with hugetlb, it is fairly common to mmap(MAP_PRIVATE) empty files and only work with anonymous pages.) -- Cheers, David / dhildenb