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(p200300d82f38ca00ca3a83da653e0234.dip0.t-ipconnect.de. [2003:d8:2f38:ca00:ca3a:83da:653e:234]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8bd1890sm12680696f8f.3.2025.07.14.08.52.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Jul 2025 08:52:57 -0700 (PDT) Message-ID: <60b0b01b-d397-4e47-8e85-295241ea3230@redhat.com> Date: Mon, 14 Jul 2025 17:52:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] mm/mseal: move madvise() logic to mm/madvise.c To: Lorenzo Stoakes Cc: Pedro Falcato , 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> <184d7f4b-6ffd-4047-b245-aec32ebda9d6@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: N0reTW3HIAv47ttbs_NnLcmoe8HBHoTqG4YPx8IwaDg_1752508379 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 47ECB1A0005 X-Stat-Signature: w5rq8c5sbcd6ufwbgaaw9jfo5s8de5gh X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1752508382-851381 X-HE-Meta: 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 xRQhq4jm uLAf5UTbIf0JH1y5p7f5tK/v5DDibiunfXtfk+ZB/JNexVqOO98ZQ1/gIiAkq6two2/yyyP8wcUwii/+HXxLjJp4jhRa5LZ+ezElPxxCCuOI6hn6mSfnIj5JrLDSk+oQdIuaIDLawyy14bbOf+ZzQlLeovRouUxjnreLglWRfrKnaasyp77iYmzssUo/euXCmxovT3KhyJSNC4pOeXE0Bkf8Lq2NGTjXnhVPRzKE3YGoMzF01NDpzHNYJt8di6f/Pp4Cu3gLORsz3SwxrvRF0RSuc3lh0BwPpJdQeLjSixR4/04tubqMU8QHOzZh4EfgK3h/mpngKxw9kpDpPGh/sEtMY87X4t/u4qhi2nlPPrGCrWoizUdYoDhqepehdt9eJl8jRLFyeeJAY4dxLVDNTKRdLAaTmwdamdo4WtJE1HoL/G5ikp/1IGfOUnm7cS2A13TAoPTqCarsPtD1Vbfnv+xRuBg== 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 17:45, Lorenzo Stoakes wrote: > On Mon, Jul 14, 2025 at 05:41:45PM +0200, David Hildenbrand wrote: >> 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. > > Well, you can mprotect() writable it again :) Isn't that what sealing ... prohibits? -- Cheers, David / dhildenb