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Mon, 21 Dec 2020 16:00:26 -0800 (PST) Received: from google.com ([2620:15c:183:200:7220:84ff:fe09:2d90]) by smtp.gmail.com with ESMTPSA id h1sm13807012ilj.8.2020.12.21.16.00.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Dec 2020 16:00:26 -0800 (PST) Date: Mon, 21 Dec 2020 17:00:22 -0700 From: Yu Zhao To: Linus Torvalds Cc: Peter Xu , Nadav Amit , Andrea Arcangeli , linux-mm , lkml , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , stable , Minchan Kim , Andy Lutomirski , Will Deacon , Peter Zijlstra Subject: Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect Message-ID: References: <76B4F49B-ED61-47EA-9BE4-7F17A26B610D@gmail.com> <9E301C7C-882A-4E0F-8D6D-1170E792065A@gmail.com> <1FCC8F93-FF29-44D3-A73A-DF943D056680@gmail.com> <20201221223041.GL6640@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: On Mon, Dec 21, 2020 at 03:33:30PM -0800, Linus Torvalds wrote: > On Mon, Dec 21, 2020 at 3:12 PM Yu Zhao wrote: > > > > I can't say I disagree with you but the man has made the call and I > > think we should just move on. > > "The man" can always be convinced by numbers. > > So if somebody comes up with an alternate patch, and explains it, and > shows that it is better - go for it. > > I just think that if mprotect() can take the mmap lock for writing, > then userfaultfd sure as hell can. What odd load does people have > where userfaultfd is more important than mprotect? > > So as far as the man is concerned, I think "just fix userfaultfd" is > simply the default obvious operation. > > Not necessarily a final endpoint. > > Linus My first instinct is to be conservative and revert 09854ba94c6a ("mm: do_wp_page() simplification") so people are less likely to come back and complain about performance issues from holding mmap lock for write when clearing pte_write. That being said, I do like the simplicity of 09854ba94c6a as well as having one simple rule that dictates what we should do when clearing pte_write(). And "userfaultfd is not the most important part of the system" is a fair point.