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=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 6DC98C2BBC7 for ; Tue, 14 Apr 2020 00:14:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 553CE20768 for ; Tue, 14 Apr 2020 00:14:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390381AbgDNANy (ORCPT ); Mon, 13 Apr 2020 20:13:54 -0400 Received: from mga04.intel.com ([192.55.52.120]:64690 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390372AbgDNANx (ORCPT ); Mon, 13 Apr 2020 20:13:53 -0400 IronPort-SDR: Tcx1HYoDFFG/1ecGXpMr1zxOB2GVLzRwBS/5G4vwoQVPIV4Z2qNJ9d4jejWxd2UPkM0dMhnXlI 6Q6Hejcy44YQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Apr 2020 17:13:53 -0700 IronPort-SDR: WwSP/bjwzVqCvzpfDJVQx7mHVD9DqAVfA90u9u6YJ0BE3eg8B7Aus6XqC75wdrzGtPX0vlI9oI I6IjfgU71shQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,380,1580803200"; d="scan'208";a="277078198" Received: from joy-optiplex-7040.sh.intel.com (HELO joy-OptiPlex-7040) ([10.239.13.16]) by fmsmga004.fm.intel.com with ESMTP; 13 Apr 2020 17:13:48 -0700 Date: Mon, 13 Apr 2020 20:04:10 -0400 From: Yan Zhao To: Christoph Hellwig Cc: Jens Axboe , Felipe Balbi , "Michael S. Tsirkin" , Jason Wang , intel-gvt-dev@lists.freedesktop.org, Felix Kuehling , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, io-uring@vger.kernel.org, linux-mm@kvack.org, Zhenyu Wang , intel-gfx@lists.freedesktop.org, linux-fsdevel@vger.kernel.org, Alex Deucher , Andrew Morton , virtualization@lists.linux-foundation.org, Linus Torvalds , Zhi Wang , Al Viro Subject: Re: [PATCH 2/6] i915/gvt/kvm: a NULL ->mm does not mean a thread is a kthread Message-ID: <20200414000410.GE10586@joy-OptiPlex-7040> Reply-To: Yan Zhao References: <20200404094101.672954-1-hch@lst.de> <20200404094101.672954-3-hch@lst.de> <20200407030845.GA10586@joy-OptiPlex-7040> <20200413132730.GB14455@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200413132730.GB14455@lst.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Apr 13, 2020 at 03:27:30PM +0200, Christoph Hellwig wrote: > On Mon, Apr 06, 2020 at 11:08:46PM -0400, Yan Zhao wrote: > > hi > > we were removing this code. see > > https://lore.kernel.org/kvm/20200313031109.7989-1-yan.y.zhao@intel.com/ > > This didn't make 5.7-rc1. > > > The implementation of vfio_dma_rw() has been in vfio next tree. > > https://github.com/awilliam/linux-vfio/commit/8d46c0cca5f4dc0538173d62cd36b1119b5105bc > > > This made 5.7-rc1, so I'll update the series to take it into account. > > T > > in vfio_dma_rw(), we still use > > bool kthread = current->mm == NULL. > > because if current->mm != NULL and current->flags & PF_KTHREAD, instead > > of calling use_mm(), we first check if (current->mm == mm) and allow copy_to_user() if it's true. > > > > Do you think it's all right? > > I can't think of another way for a kernel thread to have a mm indeed. for example, before calling to vfio_dma_rw(), a kernel thread has already called use_mm(), then its current->mm is not null, and it has flag PF_KTHREAD. in this case, we just want to allow the copy_to_user() directly if current->mm == mm, rather than call another use_mm() again. do you think it makes sense? Thanks Yan > _______________________________________________ > intel-gvt-dev mailing list > intel-gvt-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev