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Fri, 9 Jan 2026 18:10:42 +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 BJ0nCqJEYWnxBwAAD6G6ig (envelope-from ); Fri, 09 Jan 2026 18:10:42 +0000 Message-ID: <0cca73ec-00bf-4ff3-8b6a-48c723d01c35@suse.cz> Date: Fri, 9 Jan 2026 19:10:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/4] mm/vma: enforce VMA fork limit on unfaulted,faulted mremap merge too Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: "Liam R . Howlett" , Jann Horn , Pedro Falcato , Yeoreum Yun , linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Jeongjun Park , Rik van Riel , Harry Yoo References: <6e2b9b3024ae1220961c8b81d74296d4720eaf2b.1767638272.git.lorenzo.stoakes@oracle.com> 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: <6e2b9b3024ae1220961c8b81d74296d4720eaf2b.1767638272.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1137C180005 X-Stat-Signature: agnwtu53pfzyf5kose3fd71ete5d14ry X-HE-Tag: 1767982243-534041 X-HE-Meta: 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 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 1/5/26 21:11, Lorenzo Stoakes wrote: > The is_mergeable_anon_vma() function uses vmg->middle as the source > VMA. However when merging a new VMA, this field is NULL. > > In all cases except mremap(), the new VMA will either be newly established > and thus lack an anon_vma, or will be an expansion of an existing VMA thus > we do not care about whether VMA is CoW'd or not. > > In the case of an mremap(), we can end up in a situation where we can > accidentally allow an unfaulted/faulted merge with a VMA that has been > forked, violating the general rule that we do not permit this for reasons > of anon_vma lock scalability. > > Now we have the ability to be aware of the fact we are copying a VMA and > also know which VMA that is, we can explicitly check for this, so do so. > > This is pertinent since commit 879bca0a2c4f ("mm/vma: fix incorrectly > disallowed anonymous VMA merges"), as this patch permits unfaulted/faulted > merges that were previously disallowed running afoul of this issue. > > While we are here, vma_had_uncowed_parents() is a confusing name, so make > it simple and rename it to vma_is_fork_child(). > > Signed-off-by: Lorenzo Stoakes > Fixes: 879bca0a2c4f ("mm/vma: fix incorrectly disallowed anonymous VMA merges") > Cc: stable@kernel.org Acked-by: Vlastimil Babka Thanks!