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 X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1457C47080 for ; Tue, 1 Jun 2021 00:12:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8EF366102A for ; Tue, 1 Jun 2021 00:12:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232382AbhFAANp (ORCPT ); Mon, 31 May 2021 20:13:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232081AbhFAANo (ORCPT ); Mon, 31 May 2021 20:13:44 -0400 Received: from mail-pg1-x531.google.com (mail-pg1-x531.google.com [IPv6:2607:f8b0:4864:20::531]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 347DBC061574 for ; Mon, 31 May 2021 17:12:04 -0700 (PDT) Received: by mail-pg1-x531.google.com with SMTP id 29so9370840pgu.11 for ; Mon, 31 May 2021 17:12:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=McnlVW7m2tmbVr3AUvGvJWCMB+Kt1knxYWYaULI0/HQ=; b=KhY2ylKyto9r4/tMQRwmFBO2W7/XbtsevDmzDpJjYRpcYwNoP26vppfyCevbFVXlSl YHX0iHcBbz2yTCWXNf4SHE4c9Gi0phQDTs++ugOYgBp8CLk+Bj2ZO0lgPqoYXAy87MJe tsN7sEW8iJ3Mtvdr4rr9Dfycx/X1uig6DAxn1dTa8jynazagUF5GO2AjMZgY2t4crt1P 9o0gL0Kf7ssuhRXRLdY6GVquNpQHcSqCBqQCus+pOkdvA8KeMQAe6QPypM416sBarDA8 NNZ1+pjWrtauQmsZXOtv0PCQRKM9C+7/1/mAVbo0cu+EX1PuKtoFMxyW3u6a5wzT6csP z4zA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=McnlVW7m2tmbVr3AUvGvJWCMB+Kt1knxYWYaULI0/HQ=; b=LPyaT7vw81cMDNEpyry1zInKAuGOGf11A3hpqSydAphnLdMTXYQUHruPG0J2bGM/3w VvCrNrJZwumHD6KUukC9rrEBR1ugNmaZa+XAPYnyYGpd/2VHWihZLaAFMDgm/jYM/Yrp xngpobUXRwRzMXbYdMKcZsoX5nT2t7twwD2bcwH4m4BaozUQ5hXqfzqFF31Z4h8ScSka yz4BArNuiA2KsnvfIkE3XUvQCXYI5uhGCliqmICH9vqMtuVOGLw1MAfh3DLYveRaIZta YheJoY4VfCLOMunGmpacE9O33WK84r64QJRbgtC0rnR0fUTkA3flNoegr9EH5JPnRU+5 IYtA== X-Gm-Message-State: AOAM532lU7JU5aM1jlQbu7OmB13b//sxJJSBGZdRQqtc7cvLPZWuQ5jk O4EyjqJf3WflQyxhukkdBarhimBrySgMtcbLP0sPxQ== X-Google-Smtp-Source: ABdhPJzFTiOJtlNDWM8JNsJwDrcRnsvRch/y7IbVpjlDEsZVTg10xklircp6yFA+QzuAAyWgnY2hdDRiR+XbX114QMo= X-Received: by 2002:aa7:920d:0:b029:2d9:2ead:70dd with SMTP id 13-20020aa7920d0000b02902d92ead70ddmr18810656pfo.67.1622506323295; Mon, 31 May 2021 17:12:03 -0700 (PDT) MIME-Version: 1.0 References: <20210528005029.88088-1-almasrymina@google.com> <20210531162527.caeae9545ea2843c5f62bc9c@linux-foundation.org> In-Reply-To: <20210531162527.caeae9545ea2843c5f62bc9c@linux-foundation.org> From: Mina Almasry Date: Mon, 31 May 2021 17:11:52 -0700 Message-ID: Subject: Re: [PATCH v4] mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY To: Andrew Morton Cc: Axel Rasmussen , Peter Xu , Linux-MM , Mike Kravetz , open list Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 31, 2021 at 4:25 PM Andrew Morton wrote: > > On Thu, 27 May 2021 17:50:29 -0700 Mina Almasry wrote: > > > On UFFDIO_COPY, if we fail to copy the page contents while holding the > > hugetlb_fault_mutex, we will drop the mutex and return to the caller > > after allocating a page that consumed a reservation. In this case there > > may be a fault that double consumes the reservation. To handle this, we > > free the allocated page, fix the reservations, and allocate a temporary > > hugetlb page and return that to the caller. When the caller does the > > copy outside of the lock, we again check the cache, and allocate a page > > consuming the reservation, and copy over the contents. > > > > Test: > > Hacked the code locally such that resv_huge_pages underflows produce > > a warning and the copy_huge_page_from_user() always fails, then: > > > > ./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10 > > 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success > > ./tools/testing/selftests/vm/userfaultfd hugetlb 10 > > 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success > > > > Both tests succeed and produce no warnings. After the > > test runs number of free/resv hugepages is correct. > > Many conflicts here with material that is queued for 5.14-rc1. > > How serious is this problem? Is a -stable backport warranted? > I've sent 2 similar patches to the list: 1. "[PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY" This one is sent to -stable and linux-mm and is a fairly simple fix. 2. "[PATCH v4] mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY" Which is this patch. It's a more complicated and not critical fix, so not targeted for -stable. It's only sent to linux-mm. > If we decide to get this into 5.13 (and perhaps -stable) then I can > take a look at reworking all the 5.14 material on top. If not very > serious then we could rework this on top of the already queued > material. > I assume given the above we want to rework this on top of the already queued material. I can upload a v5 that is rebased on top of your branch. Note that you have an earlier version of this fix in your branch, so really this patch will turn into a fix for that patch if I rebase it (I assume that's fine).