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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 43A46C5CFC1 for ; Sun, 17 Jun 2018 22:20:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EBC53208A6 for ; Sun, 17 Jun 2018 22:20:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EBC53208A6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754147AbeFQWUP (ORCPT ); Sun, 17 Jun 2018 18:20:15 -0400 Received: from hqemgate14.nvidia.com ([216.228.121.143]:19307 "EHLO hqemgate14.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751659AbeFQWUN (ORCPT ); Sun, 17 Jun 2018 18:20:13 -0400 Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1, AES128-SHA) id ; Sun, 17 Jun 2018 15:20:19 -0700 Received: from HQMAIL107.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Sun, 17 Jun 2018 15:20:13 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Sun, 17 Jun 2018 15:20:13 -0700 Received: from [10.2.175.123] (10.2.175.123) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Sun, 17 Jun 2018 22:20:12 +0000 Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*() To: Dan Williams , CC: Matthew Wilcox , Michal Hocko , Christopher Lameter , Jason Gunthorpe , Jan Kara , Linux MM , LKML , linux-rdma , Christoph Hellwig References: <20180617012510.20139-1-jhubbard@nvidia.com> <20180617012510.20139-3-jhubbard@nvidia.com> X-Nvconfidentiality: public From: John Hubbard Message-ID: <817a7466-2abb-bc95-e7de-269420841c9b@nvidia.com> Date: Sun, 17 Jun 2018 15:19:51 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.2.175.123] X-ClientProxiedBy: HQMAIL104.nvidia.com (172.18.146.11) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/17/2018 12:53 PM, Dan Williams wrote: > [..] >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 6db729dc4c50..37576f0a4645 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1360,6 +1360,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, >> flags & TTU_SPLIT_FREEZE, page); >> } >> >> + if (PageDmaPinned(page)) >> + return false; >> /* >> * We have to assume the worse case ie pmd for invalidation. Note that >> * the page can not be free in this function as call of try_to_unmap() > > We have a similiar problem with DAX and the conclusion we came to is > that it is not acceptable for userspace to arbitrarily block kernel > actions. The conclusion there was: 'wait' if the DMA is transient, and > 'revoke' if the DMA is long lived, or otherwise 'block' long-lived DMA > if a revocation mechanism is not available. > Dan, thanks...can you please say a few words (or point to the code) about the "revoke" part of this design? And whether you think it could be applied here (instead of the unconditional appproach I have above)?