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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 466FBC4332B for ; Sat, 21 Mar 2020 08:22:41 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 11BFB20658 for ; Sat, 21 Mar 2020 08:22:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 11BFB20658 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B3F596B0003; Sat, 21 Mar 2020 04:22:40 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AEFF26B0005; Sat, 21 Mar 2020 04:22:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A2D356B0007; Sat, 21 Mar 2020 04:22:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0062.hostedemail.com [216.40.44.62]) by kanga.kvack.org (Postfix) with ESMTP id 8BBC36B0003 for ; Sat, 21 Mar 2020 04:22:40 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 28D088248068 for ; Sat, 21 Mar 2020 08:22:40 +0000 (UTC) X-FDA: 76618678080.24.wing44_8ba5d456fca55 X-HE-Tag: wing44_8ba5d456fca55 X-Filterd-Recvd-Size: 2088 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Sat, 21 Mar 2020 08:22:39 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id D1BDB68AFE; Sat, 21 Mar 2020 09:22:36 +0100 (CET) Date: Sat, 21 Mar 2020 09:22:36 +0100 From: Christoph Hellwig To: Jason Gunthorpe Cc: Christoph Hellwig , Dan Williams , Bharata B Rao , Christian =?iso-8859-1?Q?K=F6nig?= , Ben Skeggs , Jerome Glisse , kvm-ppc@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-mm@kvack.org Subject: Re: [PATCH 4/4] mm: check the device private page owner in hmm_range_fault Message-ID: <20200321082236.GB28613@lst.de> References: <20200316193216.920734-1-hch@lst.de> <20200316193216.920734-5-hch@lst.de> <20200320134109.GA30230@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200320134109.GA30230@ziepe.ca> User-Agent: Mutt/1.5.17 (2007-11-01) 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: On Fri, Mar 20, 2020 at 10:41:09AM -0300, Jason Gunthorpe wrote: > Thinking about this some more, does the locking work out here? > > hmm_range_fault() runs with mmap_sem in read, and does not lock any of > the page table levels. > > So it relies on accessing stale pte data being safe, and here we > introduce for the first time a page pointer dereference and a pgmap > dereference without any locking/refcounting. > > The get_dev_pagemap() worked on the PFN and obtained a refcount, so it > created safety. > > Is there some tricky reason this is safe, eg a DEVICE_PRIVATE page > cannot be removed from the vma without holding mmap_sem in write or > something? I don't think there is any specific protection. Let me see if we can throw in a get_dev_pagemap here - note that current mainline doesn't even use it for this path..