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b=gfFYeeixWoJd27TA/6ftiHlaFWC+5rA0IiODzPvgUlHEmM9fXsLqfIHhhtS4mVFFY9 9+N1LedbsWMnsKwt2DtVdW+IG0vVrfQsesm06TB3aTonQutexje1wiH7BB8ZOi+W2+Er HqKlopj0VtZMr5Jeq1RpaTIdEN7lttUUhWm//pR6BfP2Tz1y2NMG8PeOy1EW/B0C0iZa gB+fZa66b9HRQBHUmGb1aiGeMAhMvaPQLusZQ3fmt1ZxIh6Lkg2FPkrA/DE+ROFsEmu5 Q6FdQQmrzpTdaW9Hprc8lpfNcQFYUWVlJcLcHBCXzmHERC9JFqiCtmcZEGtDX7sGuRyS j9kg== X-Gm-Message-State: ABy/qLaJSu6JTTsEmxki4FyjU9dKx6N0kLPFqgsmVukDcxa9Hb7Aff7x LFQ3a//qLiC9H++LC2j7fuO96M84vwI= X-Google-Smtp-Source: APBJJlHcrjVsSxUzFTFx4QaDgI6yh9N4fazbh93P07JImKRnjPmhjhwgjMJtlGesIKuFtSoRWtWbpywIl+c= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:946c:be30:90d9:9093]) (user=surenb job=sendgmr) by 2002:a81:e409:0:b0:56d:5d2:1bb1 with SMTP id r9-20020a81e409000000b0056d05d21bb1mr5654ywl.2.1688606046365; Wed, 05 Jul 2023 18:14:06 -0700 (PDT) Date: Wed, 5 Jul 2023 18:13:59 -0700 In-Reply-To: <20230706011400.2949242-1-surenb@google.com> Mime-Version: 1.0 References: <20230706011400.2949242-1-surenb@google.com> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog Message-ID: <20230706011400.2949242-2-surenb@google.com> Subject: [PATCH v4 1/2] fork: lock VMAs of the parent process when forking From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: jirislaby@kernel.org, jacobly.alt@gmail.com, holger@applied-asynchrony.com, hdegoede@redhat.com, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Suren Baghdasaryan X-Rspamd-Queue-Id: 833EA8000B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: aoqrgbgu76haetwjua74f3nm1dxrdx3i X-HE-Tag: 1688606047-3829 X-HE-Meta: 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 X2MRCaaQ 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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: When forking a child process, parent write-protects an anonymous page and COW-shares it with the child being forked using copy_present_pte(). Parent's TLB is flushed right before we drop the parent's mmap_lock in dup_mmap(). If we get a write-fault before that TLB flush in the parent, and we end up replacing that anonymous page in the parent process in do_wp_page() (because, COW-shared with the child), this might lead to some stale writable TLB entries targeting the wrong (old) page. Similar issue happened in the past with userfaultfd (see flush_tlb_page() call inside do_wp_page()). Lock VMAs of the parent process when forking a child, which prevents concurrent page faults during fork operation and avoids this issue. This fix can potentially regress some fork-heavy workloads. Kernel build time did not show noticeable regression on a 56-core machine while a stress test mapping 10000 VMAs and forking 5000 times in a tight loop shows ~7% regression. If such fork time regression is unacceptable, disabling CONFIG_PER_VMA_LOCK should restore its performance. Further optimizations are possible if this regression proves to be problematic. Suggested-by: David Hildenbrand Reported-by: Jiri Slaby Closes: https://lore.kernel.org/all/dbdef34c-3a07-5951-e1ae-e9c6e3cdf51b@kernel.org/ Reported-by: Holger Hoffstätte Closes: https://lore.kernel.org/all/b198d649-f4bf-b971-31d0-e8433ec2a34c@applied-asynchrony.com/ Reported-by: Jacob Young Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217624 Fixes: 0bff0aaea03e ("x86/mm: try VMA lock-based page fault handling first") Cc: stable@vger.kernel.org Signed-off-by: Suren Baghdasaryan Reviewed-by: Liam R. Howlett Acked-by: David Hildenbrand --- kernel/fork.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index b85814e614a5..2ba918f83bde 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -658,6 +658,12 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, retval = -EINTR; goto fail_uprobe_end; } +#ifdef CONFIG_PER_VMA_LOCK + /* Disallow any page faults before calling flush_cache_dup_mm */ + for_each_vma(old_vmi, mpnt) + vma_start_write(mpnt); + vma_iter_set(&old_vmi, 0); +#endif flush_cache_dup_mm(oldmm); uprobe_dup_mmap(oldmm, mm); /*