From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 606FEC0015E for ; Sat, 8 Jul 2023 19:12:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230257AbjGHTM0 (ORCPT ); Sat, 8 Jul 2023 15:12:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55334 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230210AbjGHTMX (ORCPT ); Sat, 8 Jul 2023 15:12:23 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D7726FF for ; Sat, 8 Jul 2023 12:12:21 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-573d70da2afso32392777b3.2 for ; Sat, 08 Jul 2023 12:12:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1688843541; x=1691435541; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=oTV0xihdJDZ3LmT5b0VvbfWVPo2l/pYZxiWhaA2z/Wc=; b=1k2h2Lzi2Y7Zso2QCXABxD6tKxYBi69Od4eg/BJzd/oZKr/yo1QC9zYTy+F7bkwUsr MJ4Cs8yuMwfbeH9sKlCNAwVo49wzFYe05nOmOIFdL12CZV8/kFSu5wJrvCOBni6b6XLW llu6z1SxXl9jUD2la6uHivLOfnp3yDTzL+wbIb/uZmz+uMYQ0KGYXgadTEUmWm9Uz2p8 OvPqWDoLPuHzUoISVlQIJ3HwqRiXh8i6S85Nr9mydxCOVHJ3byBf5nAejApz8KtI+7VG nVka+9EAa6kAPb4o2CIYQlx+qV3ecK270Nq5eVaYu0hTPSFmvNlGf9LGupgmu1sf8Ore 83wA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688843541; x=1691435541; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=oTV0xihdJDZ3LmT5b0VvbfWVPo2l/pYZxiWhaA2z/Wc=; b=lg1pjAVblzR8WDKyLqXxYKE20KEdJBFT2YDx9ERnXNvSkX0K7Xn6/ItPdeVDXuAQC8 cxMhmx9X+ZILHob7FfOF34X0PJai5Iri7o5tKE/+XZf389qepszt8ZP1i3TRiG6zHtJV cYaM/7XCdOihYqYtP05FMICniXSLcSVJmazhQi6J0rai/edh6tYi4Q/1roaBmu1Te+qb xc9rpJCp+DEIyUrezhqz1Cltb4YCkJymMW8KPbFHSO9P9Z8QTqlK7s3ydB1zMHKjExCN 0bPB62XY7qruO8ni+abhPMSf5kj+/C751PNunL8weZMRkxm2GMZLS3JE+6naoILrp107 oS1A== X-Gm-Message-State: ABy/qLZHMO0GXf+LIkd7q229mys2oZs/1cb66Zi5/mYOKhiiKuKlIMhL GlRHace3QdMRfWUlBE+/cKNBragYYOY= X-Google-Smtp-Source: APBJJlHVrRFpZyyO6dwy1Gjn4/30Rl1D+ek+P+dzMKAoVpdfL0WWnvznDWyGgdeVaC3RV2FWAanbuAUiF7I= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:6f0:5193:79db:25b3]) (user=surenb job=sendgmr) by 2002:a81:ac20:0:b0:565:b269:5ef7 with SMTP id k32-20020a81ac20000000b00565b2695ef7mr58334ywh.1.1688843541040; Sat, 08 Jul 2023 12:12:21 -0700 (PDT) Date: Sat, 8 Jul 2023 12:12:12 -0700 In-Reply-To: <20230708191212.4147700-1-surenb@google.com> Mime-Version: 1.0 References: <20230708191212.4147700-1-surenb@google.com> X-Mailer: git-send-email 2.41.0.390.g38632f3daf-goog Message-ID: <20230708191212.4147700-3-surenb@google.com> Subject: [PATCH v2 3/3] fork: lock VMAs of the parent process when forking From: Suren Baghdasaryan To: torvalds@linux-foundation.org Cc: akpm@linux-foundation.org, regressions@leemhuis.info, bagasdotme@gmail.com, jacobly.alt@gmail.com, willy@infradead.org, liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com, ldufour@linux.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, gregkh@linuxfoundation.org, regressions@lists.linux.dev, Suren Baghdasaryan , Jiri Slaby , "=?UTF-8?q?Holger=20Hoffst=C3=A4tte?=" , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 ~5% 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@ke= rnel.org/ Reported-by: Holger Hoffst=C3=A4tte Closes: https://lore.kernel.org/all/b198d649-f4bf-b971-31d0-e8433ec2a34c@ap= plied-asynchrony.com/ Reported-by: Jacob Young Closes: https://bugzilla.kernel.org/show_bug.cgi?id=3D217624 Fixes: 0bff0aaea03e ("x86/mm: try VMA lock-based page fault handling first"= ) Cc: stable@vger.kernel.org Signed-off-by: Suren Baghdasaryan --- kernel/fork.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/fork.c b/kernel/fork.c index b85814e614a5..d2e12b6d2b18 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -686,6 +686,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *= mm, for_each_vma(old_vmi, mpnt) { struct file *file; =20 + vma_start_write(mpnt); if (mpnt->vm_flags & VM_DONTCOPY) { vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt)); continue; --=20 2.41.0.390.g38632f3daf-goog