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Mon, 21 Dec 2020 13:24:38 -0800 (PST) Received: from google.com ([2620:15c:183:200:7220:84ff:fe09:2d90]) by smtp.gmail.com with ESMTPSA id t2sm14659937ili.31.2020.12.21.13.24.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Dec 2020 13:24:38 -0800 (PST) Date: Mon, 21 Dec 2020 14:24:34 -0700 From: Yu Zhao To: Linus Torvalds Cc: Nadav Amit , Peter Xu , 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: <20201221172711.GE6640@xz-x1> <76B4F49B-ED61-47EA-9BE4-7F17A26B610D@gmail.com> <9E301C7C-882A-4E0F-8D6D-1170E792065A@gmail.com> 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 12:26:22PM -0800, Linus Torvalds wrote: > On Mon, Dec 21, 2020 at 12:23 PM Nadav Amit wrote: > > > > Using mmap_write_lock() was my initial fix and there was a strong pushback > > on this approach due to its potential impact on performance. > > From whom? > > Somebody who doesn't understand that correctness is more important > than performance? And that userfaultfd is not the most important part > of the system? > > The fact is, userfaultfd is CLEARLY BUGGY. > > Linus Fair enough. Nadav, for your patch (you might want to update the commit message). Reviewed-by: Yu Zhao While we are all here, there is also clear_soft_dirty() that could use a similar fix...