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Thu, 10 Jul 2025 14:24:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id IfK7BSzNb2g0MwAAD6G6ig (envelope-from ); Thu, 10 Jul 2025 14:24:44 +0000 Message-ID: <478a6003-7dc8-444c-b8a6-a29c521abe72@suse.cz> Date: Thu, 10 Jul 2025 16:24:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 05/10] mm/mremap: use an explicit uffd failure path for mremap Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: Peter Xu , Alexander Viro , Christian Brauner , Jan Kara , "Liam R . Howlett" , Jann Horn , Pedro Falcato , Rik van Riel , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: EFD1D16000C X-Stat-Signature: 7iigcpuue1u1orspqr1u9f5td8at1thd X-Rspam-User: X-HE-Tag: 1752157485-637054 X-HE-Meta: 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 2hTjzVbd hYtF2L8aydOxt+Cd1rbo3jVcScBv7+9cWhXeHOBD6voV0ESa0lsDDOLJjQpO7G7AwfH4u474w+D0WdgNmvM+EA+UFo3qEtWCU0yl5BrGDX8yqTZEEsmCf3wuHKVqEQRe7IVdwMNQmYdoPPxjx4mp44OE9LnLVCCNSSmN6zX/ZC/5CJqYS4uNoB3puE+obswDufF0vutzUW65MieimUv2UFsW3Jj6fT08YgrRlMfF73Du4BuycweOqA8zHuCC5IYbqYtrykB3wZre1VGC0nu06UxzmpE+dTTbYUFsGfXUrEWjmXNTyDunLSblvRCDagS7OWF6115SX7Q/69lO9tI5vOHH3Wcn4SjH2ljGF1/qwki7r3QQ= 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 7/7/25 07:27, Lorenzo Stoakes wrote: > Right now it appears that the code is relying upon the returned destination > address having bits outside PAGE_MASK to indicate whether an error value is > specified, and decrementing the increased refcount on the uffd ctx if so. > > This is not a safe means of determining an error value, so instead, be > specific. It makes far more sense to do so in a dedicated error path, so > add mremap_userfaultfd_fail() for this purpose and use this when an error > arises. > > A vm_userfaultfd_ctx is not established until we are at the point where > mremap_userfaultfd_prep() is invoked in copy_vma_and_data(), so this is a > no-op until this happens. > > That is - uffd remap notification only occurs if the VMA is actually moved > - at which point a UFFD_EVENT_REMAP event is raised. > > No errors can occur after this point currently, though it's certainly not > guaranteed this will always remain the case, and we mustn't rely on this. > > However, the reason for needing to handle this case is that, when an error > arises on a VMA move at the point of adjusting page tables, we revert this > operation, and propagate the error. > > At this point, it is not correct to raise a uffd remap event, and we must > handle it. > > This refactoring makes it abundantly clear what we are doing. > > We assume vrm->new_addr is always valid, which a prior change made the case > even for mremap() invocations which don't move the VMA, however given no > uffd context would be set up in this case it's immaterial to this change > anyway. > > No functional change intended. > > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka Guess that renders my previous nit unimportant.