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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8974C433F5 for ; Tue, 29 Mar 2022 16:44:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E8F788D0002; Tue, 29 Mar 2022 12:44:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E19918D0001; Tue, 29 Mar 2022 12:44:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C440D8D0002; Tue, 29 Mar 2022 12:44:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id AEDD98D0001 for ; Tue, 29 Mar 2022 12:44:38 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 723BF182888A6 for ; Tue, 29 Mar 2022 16:44:38 +0000 (UTC) X-FDA: 79297997436.24.7AC6B7E Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf14.hostedemail.com (Postfix) with ESMTP id ECD8C100014 for ; Tue, 29 Mar 2022 16:44:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1648572277; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=RVY7rMpGFn52vdQ2M3hw/PWs92e8BoddZH/fcoM4f7g=; b=Ym5chToCNoVSymBxsBBrUXO7xCgGUIhLG8zvbK1aneFIdAIA6k+hojjhkjhvaGypzUBuo+ u+k9VOhw/J5IS8jvB33PAtTglha/Xgz0CfpqbgBm1ZZ1ZzgByCJLUEY3HPnuJicmCwv2pA OoZg4f6fN1rgLHIPz7WY8ghyhj8yuGM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-542-JHxNB2iVMtKGFGYz0rnuuA-1; Tue, 29 Mar 2022 12:44:35 -0400 X-MC-Unique: JHxNB2iVMtKGFGYz0rnuuA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9289C803524; Tue, 29 Mar 2022 16:44:33 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.134]) by smtp.corp.redhat.com (Postfix) with ESMTP id B31D6112132D; Tue, 29 Mar 2022 16:43:31 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Pedro Gomes , Oded Gabbay , Catalin Marinas , Will Deacon , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Gerald Schaefer , linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, David Hildenbrand Subject: [PATCH v2 0/8] mm: COW fixes part 3: reliable GUP R/W FOLL_GET of anonymous pages Date: Tue, 29 Mar 2022 18:43:21 +0200 Message-Id: <20220329164329.208407-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Stat-Signature: 33zrrnbio56euofjzrqg9zrqjfafeph6 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: ECD8C100014 Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Ym5chToC; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf14.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Rspam-User: X-HE-Tag: 1648572277-322052 Content-Transfer-Encoding: quoted-printable 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: More information on the general COW issues can be found at [2]. This seri= es is based on latest linus/master and [1]: [PATCH v3 00/16] mm: COW fixes part 2: reliable GUP pins of anonymous pages v2 is located at: https://github.com/davidhildenbrand/linux/tree/cow_fixes_part_3_v2 This series fixes memory corruptions when a GUP R/W reference (FOLL_WRITE | FOLL_GET) was taken on an anonymous page and COW logic fail= s to detect exclusivity of the page to then replacing the anonymous page by a copy in the page table: The GUP reference lost synchronicity with the pages mapped into the page tables. This series focuses on x86, arm64, s390x and ppc64/book3s -- other architectures are fairly easy to support by implementing __HAVE_ARCH_PTE_SWP_EXCLUSIVE. This primarily fixes the O_DIRECT memory corruptions that can happen on concurrent swapout, whereby we lose DMA reads to a page (modifying the us= er page by writing to it). O_DIRECT currently uses FOLL_GET for short-term (!FOLL_LONGTERM) DMA from/to a user page. In the long run, we want to convert it to proper= ly use FOLL_PIN, and John is working on it, but that might take a while and might not be easy to backport. In the meantime, let's restore what used t= o work before we started modifying our COW logic: make R/W FOLL_GET references reliable as long as there is no fork() after GUP involved. This is just the natural follow-up of part 2, that will also further reduce "wrong COW" on the swapin path, for example, when we cannot remove a page from the swapcache due to concurrent writeback, or if we have two threads faulting on the same swapped-out page. Fixing O_DIRECT is just a nice side-product This issue, including other related COW issues, has been summarized in [3= ] under 2): " 2. Intra Process Memory Corruptions due to Wrong COW (FOLL_GET) It was discovered that we can create a memory corruption by reading a file via O_DIRECT to a part (e.g., first 512 bytes) of a page, concurrently writing to an unrelated part (e.g., last byte) of the same page, and concurrently write-protecting the page via clear_refs SOFTDIRTY tracking [6]. For the reproducer, the issue is that O_DIRECT grabs a reference of the target page (via FOLL_GET) and clear_refs write-protects the relevant page table entry. On successive write access to the page from the process itself, we wrongly COW the page when resolving the write fault, resulting in a loss of synchronicity and consequently a memory corrupti= on. While some people might think that using clear_refs in this combination is a corner cases, it turns out to be a more generic problem unfortunat= ely. For example, it was just recently discovered that we can similarly create a memory corruption without clear_refs, simply by concurrently swapping out the buffer pages [7]. Note that we nowadays even use the swap infrastructure in Linux without an actual swap disk/partition: the prime example is zram which is enabled as default under Fedora [10]. The root issue is that a write-fault on a page that has additional references results in a COW and thereby a loss of synchronicity and consequently a memory corruption if two parties believe they are referencing the same page. " We don't particularly care about R/O FOLL_GET references: they were never reliable and O_DIRECT doesn't expect to observe modifications from a page after DMA was started. Note that: * this only fixes the issue on x86, arm64, s390x and ppc64/book3s ("enterprise architectures"). Other architectures have to implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE to achieve the same. * this does *not * consider any kind of fork() after taking the reference= : fork() after GUP never worked reliably with FOLL_GET. * Not losing PG_anon_exclusive during swapout was the last remaining piece. KSM already makes sure that there are no other references on a page before considering it for sharing. Page migration maintains PG_anon_exclusive and simply fails when there are additional references (freezing the refcount fails). Only swapout code dropped the PG_anon_exclusive flag because it requires more work to remember + restore it. With this series in place, most COW issues of [3] are fixed on said architectures. Other architectures can implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE fairly easily. [1] https://lkml.kernel.org/r/20220329160440.193848-1-david@redhat.com [2] https://lkml.kernel.org/r/20211217113049.23850-1-david@redhat.com [3] https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat= .com v2 -> v3: * Rebased and retested * "arm64/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE" -> Add RB and a comment to the patch description * "s390/pgtable: cleanup description of swp pte layout" -> Added * "s390/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE" -> Use new set_pte_bit()/clear_pte_bit() -> Fixups comments/patch description David Hildenbrand (8): mm/swap: remember PG_anon_exclusive via a swp pte bit mm/debug_vm_pgtable: add tests for __HAVE_ARCH_PTE_SWP_EXCLUSIVE x86/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE arm64/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE s390/pgtable: cleanup description of swp pte layout s390/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE powerpc/pgtable: remove _PAGE_BIT_SWAP_TYPE for book3s powerpc/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE for book3s arch/arm64/include/asm/pgtable-prot.h | 1 + arch/arm64/include/asm/pgtable.h | 23 ++++++-- arch/powerpc/include/asm/book3s/64/pgtable.h | 31 ++++++++--- arch/s390/include/asm/pgtable.h | 36 +++++++++---- arch/x86/include/asm/pgtable.h | 16 ++++++ arch/x86/include/asm/pgtable_64.h | 4 +- arch/x86/include/asm/pgtable_types.h | 5 ++ include/linux/pgtable.h | 29 +++++++++++ include/linux/swapops.h | 2 + mm/debug_vm_pgtable.c | 15 ++++++ mm/memory.c | 55 ++++++++++++++++++-- mm/rmap.c | 19 ++++--- mm/swapfile.c | 13 ++++- 13 files changed, 216 insertions(+), 33 deletions(-) --=20 2.35.1