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Fri, 21 Apr 2023 09:01:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id EjYjG+dQQmQrQQAAMHmgww (envelope-from ); Fri, 21 Apr 2023 09:01:27 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id CD5DAA0729; Fri, 21 Apr 2023 11:01:26 +0200 (CEST) Date: Fri, 21 Apr 2023 11:01:26 +0200 From: Jan Kara To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Andy Lutomirski Subject: Re: [RFC PATCH 0/3] permit write-sealed memfd read-only shared mappings Message-ID: <20230421090126.tmem27kfqamkdaxo@quack3> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: D4FBD1C002C X-Rspamd-Server: rspam01 X-Stat-Signature: xo94pyeyyeuhyj85pbmzdfmrazomxqt6 X-HE-Tag: 1682067688-528526 X-HE-Meta: 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 8t8dEDOj lqesFC+Yi2AuYPL/OW3j762Fa+OWTdNaW4mXt0f02yu1F7mxkRI0dInLqPzOiRxbfAD1gn7d3TrWsaYdgkJrOr1f+PgWA/KCeAiOAuaLOZ67VLHutmeK97w763xz1BqrcqzlGvjv5CF9LERnK+OkP/4dEVKWO1DWh+wHIP/zo7RQ2KWhe7VFbo4QB42RjN2Pv3D0tGNvkQOwrABR8sdOHJweysJxmnxn+gNkNr0wToaLA9bDH57BS8O0wNg== 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: Hi! On Mon 03-04-23 23:28:29, Lorenzo Stoakes wrote: > This patch series is in two parts:- > > 1. Currently there are a number of places in the kernel where we assume > VM_SHARED implies that a mapping is writable. Let's be slightly less > strict and relax this restriction in the case that VM_MAYWRITE is not > set. > > This should have no noticeable impact as the lack of VM_MAYWRITE implies > that the mapping can not be made writable via mprotect() or any other > means. > > 2. Align the behaviour of F_SEAL_WRITE and F_SEAL_FUTURE_WRITE on mmap(). > The latter already clears the VM_MAYWRITE flag for a sealed read-only > mapping, we simply extend this to F_SEAL_WRITE too. > > For this to have effect, we must also invoke call_mmap() before > mapping_map_writable(). > > As this is quite a fundamental change on the assumptions around VM_SHARED > and since this causes a visible change to userland (in permitting read-only > shared mappings on F_SEAL_WRITE mappings), I am putting forward as an RFC > to see if there is anything terribly wrong with it. So what I miss in this series is what the motivation is. Is it that you need to map F_SEAL_WRITE read-only? Why? Honza -- Jan Kara SUSE Labs, CR