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=-6.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS 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 07F1EC47082 for ; Mon, 31 May 2021 23:25:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E308F61287 for ; Mon, 31 May 2021 23:25:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232207AbhEaX1K (ORCPT ); Mon, 31 May 2021 19:27:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:46854 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231144AbhEaX1I (ORCPT ); Mon, 31 May 2021 19:27:08 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8DE676127C; Mon, 31 May 2021 23:25:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1622503527; bh=c7naDVv/eC6perkruWntIRarp9ADf3gqHd+mZMh5/1g=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=f86MkgRpXm8WajcJUugg9vDhDy2s4dJ8YWA2yzT+eXYvlf8iJzz/mb7VLpuXhVLMM r1mPJtC6+ZRiXaMzUzM1cAeBZ+ijw/qdvmiD6bG9iphl/kqf8+Ve/6RZRuEHm1X8Hj 3iGOJHRyHcWH/hbkvpVI1CnDrrKLpHbls90I/bII= Date: Mon, 31 May 2021 16:25:27 -0700 From: Andrew Morton To: Mina Almasry Cc: Axel Rasmussen , Peter Xu , linux-mm@kvack.org, Mike Kravetz , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY Message-Id: <20210531162527.caeae9545ea2843c5f62bc9c@linux-foundation.org> In-Reply-To: <20210528005029.88088-1-almasrymina@google.com> References: <20210528005029.88088-1-almasrymina@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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.