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Mon, 10 Nov 2025 15:51:27 +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 MzPiFP8JEmnZYQAAD6G6ig (envelope-from ); Mon, 10 Nov 2025 15:51:27 +0000 Message-ID: <945fbe45-1ee7-4108-b01a-a8d2b0bb9cfe@suse.cz> Date: Mon, 10 Nov 2025 16:51:27 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/8] mm: add atomic VMA flags and set VM_MAYBE_GUARD as such Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: Jonathan Corbet , David Hildenbrand , "Liam R . Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jann Horn , Pedro Falcato , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrei Vagin 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-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[27]; FREEMAIL_CC(0.00)[lwn.net,redhat.com,oracle.com,kernel.org,google.com,suse.com,goodmis.org,efficios.com,suse.de,nvidia.com,linux.alibaba.com,arm.com,linux.dev,vger.kernel.org,kvack.org,gmail.com]; RCVD_TLS_ALL(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RL37wz1aou84on4nnr4peu14t5)]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[oracle.com:email,imap1.dmz-prg2.suse.org:helo,suse.cz:email,suse.cz:mid,suse.de:email] X-Spam-Flag: NO X-Spam-Score: -4.30 On 11/7/25 17:11, Lorenzo Stoakes wrote: > This patch adds the ability to atomically set VMA flags with only the mmap > read/VMA read lock held. > > As this could be hugely problematic for VMA flags in general given that all > other accesses are non-atomic and serialised by the mmap/VMA locks, we > implement this with a strict allow-list - that is, only designated flags > are allowed to do this. > > We make VM_MAYBE_GUARD one of these flags. > > Reviewed-by: Pedro Falcato > Reviewed-by: Vlastimil Babka > Signed-off-by: Lorenzo Stoakes > --- > include/linux/mm.h | 42 ++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 42 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 2a5516bff75a..699566c21ff7 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -518,6 +518,9 @@ extern unsigned int kobjsize(const void *objp); > /* This mask represents all the VMA flag bits used by mlock */ > #define VM_LOCKED_MASK (VM_LOCKED | VM_LOCKONFAULT) > > +/* These flags can be updated atomically via VMA/mmap read lock. */ > +#define VM_ATOMIC_SET_ALLOWED VM_MAYBE_GUARD > + > /* Arch-specific flags to clear when updating VM flags on protection change */ > #ifndef VM_ARCH_CLEAR > # define VM_ARCH_CLEAR VM_NONE > @@ -860,6 +863,45 @@ static inline void vm_flags_mod(struct vm_area_struct *vma, > __vm_flags_mod(vma, set, clear); > } > > +static inline bool __vma_flag_atomic_valid(struct vm_area_struct *vma, > + int bit) > +{ > + const vm_flags_t mask = BIT(bit); > + > + /* Only specific flags are permitted */ > + if (WARN_ON_ONCE(!(mask & VM_ATOMIC_SET_ALLOWED))) > + return false; > + > + return true; > +} > + > +/* > + * Set VMA flag atomically. Requires only VMA/mmap read lock. Only specific > + * valid flags are allowed to do this. > + */ > +static inline void vma_flag_set_atomic(struct vm_area_struct *vma, int bit) > +{ > + /* mmap read lock/VMA read lock must be held. */ > + if (!rwsem_is_locked(&vma->vm_mm->mmap_lock)) > + vma_assert_locked(vma); > + > + if (__vma_flag_atomic_valid(vma, bit)) > + set_bit(bit, &vma->__vm_flags); > +} > + > +/* > + * Test for VMA flag atomically. Requires no locks. Only specific valid flags > + * are allowed to do this. > + * > + * This is necessarily racey, so callers must ensure that serialisation is > + * achieved through some other means, or that races are permissible. > + */ > +static inline bool vma_flag_test_atomic(struct vm_area_struct *vma, int bit) > +{ > + if (__vma_flag_atomic_valid(vma, bit)) > + return test_bit(bit, &vma->__vm_flags); > +} Hm clang is unhappy here. ./include/linux/mm.h:932:1: error: non-void function does not return a value in all control paths [-Werror,-Wreturn-type] 932 | } | ^ 1 error generated. I don't have CONFIG_WERROR enabled though, so not sure why it's not just a warning, as the function is unused until patch 5/8 which adds a "return false" here. So it's just a potential bisection annoyance with clang. Andrew could you move that hunk from to this patch? Thanks. > + > static inline void vma_set_anonymous(struct vm_area_struct *vma) > { > vma->vm_ops = NULL;