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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 A9675C43215 for ; Wed, 13 Nov 2019 19:17:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11F4D20679 for ; Wed, 13 Nov 2019 19:17:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726599AbfKMTRJ (ORCPT ); Wed, 13 Nov 2019 14:17:09 -0500 Received: from mga11.intel.com ([192.55.52.93]:15422 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbfKMTRJ (ORCPT ); Wed, 13 Nov 2019 14:17:09 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Nov 2019 11:17:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,301,1569308400"; d="scan'208";a="379324206" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga005.jf.intel.com with ESMTP; 13 Nov 2019 11:17:06 -0800 Date: Wed, 13 Nov 2019 11:17:06 -0800 From: Ira Weiny To: Jason Gunthorpe , John Hubbard Cc: John Hubbard , Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Jan Kara , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML Subject: Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM Message-ID: <20191113191705.GE12947@iweiny-DESK2.sc.intel.com> References: <20191113042710.3997854-1-jhubbard@nvidia.com> <20191113042710.3997854-9-jhubbard@nvidia.com> <20191113130202.GA26068@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191113130202.GA26068@ziepe.ca> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Wed, Nov 13, 2019 at 09:02:02AM -0400, Jason Gunthorpe wrote: > On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote: > > As it says in the updated comment in gup.c: current FOLL_LONGTERM > > behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the > > FS DAX check requirement on vmas. > > > > However, the corresponding restriction in get_user_pages_remote() was > > slightly stricter than is actually required: it forbade all > > FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers > > that do not set the "locked" arg. > > > > Update the code and comments accordingly, and update the VFIO caller > > to take advantage of this, fixing a bug as a result: the VFIO caller > > is logically a FOLL_LONGTERM user. > > > > Also, remove an unnessary pair of calls that were releasing and > > reacquiring the mmap_sem. There is no need to avoid holding mmap_sem > > just in order to call page_to_pfn(). > > > > Also, move the DAX check ("if a VMA is DAX, don't allow long term > > pinning") from the VFIO call site, all the way into the internals > > of get_user_pages_remote() and __gup_longterm_locked(). That is: > > get_user_pages_remote() calls __gup_longterm_locked(), which in turn > > calls check_dax_vmas(). It's lightly explained in the comments as well. > > > > Thanks to Jason Gunthorpe for pointing out a clean way to fix this, > > and to Dan Williams for helping clarify the DAX refactoring. > > > > Suggested-by: Jason Gunthorpe > > Cc: Dan Williams > > Cc: Jerome Glisse > > Cc: Ira Weiny > > Signed-off-by: John Hubbard > > drivers/vfio/vfio_iommu_type1.c | 25 ++----------------------- > > mm/gup.c | 27 ++++++++++++++++++++++----- > > 2 files changed, 24 insertions(+), 28 deletions(-) > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > > index d864277ea16f..7301b710c9a4 100644 > > +++ b/drivers/vfio/vfio_iommu_type1.c > > @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > > { > > struct page *page[1]; > > struct vm_area_struct *vma; > > - struct vm_area_struct *vmas[1]; > > unsigned int flags = 0; > > int ret; > > > > @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > > flags |= FOLL_WRITE; > > > > down_read(&mm->mmap_sem); > > - if (mm == current->mm) { > > - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, > > - vmas); > > - } else { > > - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, > > - vmas, NULL); > > - /* > > - * The lifetime of a vaddr_get_pfn() page pin is > > - * userspace-controlled. In the fs-dax case this could > > - * lead to indefinite stalls in filesystem operations. > > - * Disallow attempts to pin fs-dax pages via this > > - * interface. > > - */ > > - if (ret > 0 && vma_is_fsdax(vmas[0])) { > > - ret = -EOPNOTSUPP; > > - put_page(page[0]); > > - } > > - } > > - up_read(&mm->mmap_sem); > > - > > + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, > > + page, NULL, NULL); > > if (ret == 1) { > > *pfn = page_to_pfn(page[0]); > > return 0; > > Mind the return with the lock held this needs some goto unwind Ah yea... retract my reviewed by... :-( Ira