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 9BBDCC47082 for ; Tue, 1 Jun 2021 00:36:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 78E3161364 for ; Tue, 1 Jun 2021 00:36:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232515AbhFAAif (ORCPT ); Mon, 31 May 2021 20:38:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:35194 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232446AbhFAAid (ORCPT ); Mon, 31 May 2021 20:38:33 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id D380F6124B; Tue, 1 Jun 2021 00:36:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1622507813; bh=vcDVecllsyG6dl5tUH0HL/qOl+Lovf/V3ktxDvPMV30=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=XWnGUr8lks1OLZCW9x42MeS9dKXPOt/EGofJqiMObT/X690JH+OGZ50ZygOhct5+R zUSqFswaRwzKU9OXbeRdDhLBYwFDByklCXy5/tOCELE/Sii8RoWvSEgNbGLe0qTTM7 Pol7ZvLKfSLkoOUX+VAf8mWh2wc1YfPL3TtqiI7w= Date: Mon, 31 May 2021 17:36:52 -0700 From: Andrew Morton To: Mina Almasry Cc: Axel Rasmussen , Peter Xu , Linux-MM , Mike Kravetz , open list Subject: Re: [PATCH v4] mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY Message-Id: <20210531173652.c21404a16a8f8542ce40afa8@linux-foundation.org> In-Reply-To: References: <20210528005029.88088-1-almasrymina@google.com> <20210531162527.caeae9545ea2843c5f62bc9c@linux-foundation.org> 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 Mon, 31 May 2021 17:11:52 -0700 Mina Almasry wrote: > 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" Ah, OK, the title of the first patch was changed, which threw me off. I'd skipped "[PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY" because Mike's comments appeared to require a v5. I applied it and made Mike's changelog suggestions. Queued for 5.13 and -stable. And I queued "[PATCH v4] mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY" for 5.14.