From patchwork Mon Nov 25 04:19:57 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Hubbard X-Patchwork-Id: 11259601 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5AC4A138C for ; Mon, 25 Nov 2019 04:20:50 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1BC6F20815 for ; Mon, 25 Nov 2019 04:20:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="PuFsLnuG" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1BC6F20815 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2521E6B0590; Sun, 24 Nov 2019 23:20:24 -0500 (EST) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id 2045B6B0591; Sun, 24 Nov 2019 23:20:24 -0500 (EST) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 11A4E6B0592; Sun, 24 Nov 2019 23:20:24 -0500 (EST) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0196.hostedemail.com [216.40.44.196]) by kanga.kvack.org (Postfix) with ESMTP id F04DE6B0590 for ; Sun, 24 Nov 2019 23:20:23 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 92038180AD81F for ; Mon, 25 Nov 2019 04:20:23 +0000 (UTC) X-FDA: 76193497926.02.fight36_5aa2835e24427 X-Spam-Summary: 1,0,0,,d41d8cd98f00b204,jhubbard@nvidia.com,:akpm@linux-foundation.org:viro@zeniv.linux.org.uk:alex.williamson@redhat.com:benh@kernel.crashing.org:bjorn.topel@intel.com:hch@infradead.org:dan.j.williams@intel.com:daniel@ffwll.ch:david@fromorbit.com:airlied@linux.ie:davem@davemloft.net:ira.weiny@intel.com:jack@suse.cz:jgg@ziepe.ca:axboe@kernel.dk:corbet@lwn.net:jglisse@redhat.com:magnus.karlsson@intel.com:mchehab@kernel.org:mpe@ellerman.id.au:mhocko@suse.com:mike.kravetz@oracle.com:paulus@samba.org:shuah@kernel.org:vbabka@suse.cz: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-kernel@vger.kernel.org:jhubbard@nvidia.com:jgg@mellanox.com,RULES_HIT:30012:30054:30064:30070:30079:30090,0,RBL:216.228.121.64:@nvidia.co m:.lbl8. 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Miller" , Ira Weiny , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?utf-8?b?SsOpcsO0bWUgR2xpc3Nl?= , Magnus Karlsson , "Mauro Carvalho Chehab" , Michael Ellerman , Michal Hocko , Mike Kravetz , "Paul Mackerras" , Shuah Khan , Vlastimil Babka , , , , , , , , , , , , , LKML , John Hubbard , "Jason Gunthorpe" Subject: [PATCH 05/19] mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM Date: Sun, 24 Nov 2019 20:19:57 -0800 Message-ID: <20191125042011.3002372-6-jhubbard@nvidia.com> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191125042011.3002372-1-jhubbard@nvidia.com> References: <20191125042011.3002372-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1574655612; bh=l4ZzqtVW71Fwvoz1qyCbd1xWWEz8EY4C2cUJdAbaFHs=; h=X-PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:X-NVConfidentiality: Content-Transfer-Encoding:Content-Type; b=PuFsLnuGu1KfB/ZC9izxEq0bMZSKw8FTNCw9beyt6bkUSDvoRbbiuS99SR7As24lu RGbHmieWvPTXU5e+mq74L8miXctdPbS0ioC326V6mLcvZoRfydtyo4rIwM2R6Jm6Y6 23VRYgCcNYQIW4DAuRBJaAfOxnfr8ibm/Si4ea/2FO0GHPZEt26wKzvbdKSJFb3SoI OQDgSp3ubf0/3+PrrJl2Ax3wUIMAX6Tzpjfxed19Rt0JuaQHyvhUbCzkCSmjSgb7lq 2blCTd3N7xpKdUogXl+J6b4iDitiVq0ZaMwEly1saing+z2ZeMaF4JaRAtrZQeE9F4 nJz2PdoULdpQA== 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: 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 to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy 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(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Tested-by: Alex Williamson Acked-by: Alex Williamson Reviewed-by: Jason Gunthorpe Reviewed-by: Ira Weiny Suggested-by: Jason Gunthorpe Cc: Dan Williams Cc: Jerome Glisse Signed-off-by: John Hubbard --- mm/gup.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 3ecce297a47f..c0c56888e7cc 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -29,6 +29,13 @@ struct follow_page_context { unsigned int page_mask; }; +static __always_inline long __gup_longterm_locked(struct task_struct *tsk, + struct mm_struct *mm, + unsigned long start, + unsigned long nr_pages, + struct page **pages, + struct vm_area_struct **vmas, + unsigned int flags); /* * Return the compound head page with ref appropriately incremented, * or NULL if that failed. @@ -1179,13 +1186,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, struct vm_area_struct **vmas, int *locked) { /* - * FIXME: Current FOLL_LONGTERM behavior is incompatible with + * Parts of FOLL_LONGTERM behavior are incompatible with * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on - * vmas. As there are no users of this flag in this call we simply - * disallow this option for now. + * vmas. However, this only comes up if locked is set, and there are + * callers that do request FOLL_LONGTERM, but do not set locked. So, + * allow what we can. */ - if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM)) - return -EINVAL; + if (gup_flags & FOLL_LONGTERM) { + if (WARN_ON_ONCE(locked)) + return -EINVAL; + /* + * This will check the vmas (even if our vmas arg is NULL) + * and return -ENOTSUPP if DAX isn't allowed in this case: + */ + return __gup_longterm_locked(tsk, mm, start, nr_pages, pages, + vmas, gup_flags | FOLL_TOUCH | + FOLL_REMOTE); + } return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, locked,