From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=xzJI=55=vger.kernel.org=io-uring-owner@kernel.org>
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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,
	USER_AGENT_SANE_1 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 B2508C2BBC7
	for <io-uring@archiver.kernel.org>; Mon, 13 Apr 2020 13:27:35 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id 9C03E2075E
	for <io-uring@archiver.kernel.org>; Mon, 13 Apr 2020 13:27:35 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1729848AbgDMN1f (ORCPT <rfc822;io-uring@archiver.kernel.org>);
        Mon, 13 Apr 2020 09:27:35 -0400
Received: from verein.lst.de ([213.95.11.211]:34773 "EHLO verein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1728649AbgDMN1e (ORCPT <rfc822;io-uring@vger.kernel.org>);
        Mon, 13 Apr 2020 09:27:34 -0400
Received: by verein.lst.de (Postfix, from userid 2407)
        id AEBD868BEB; Mon, 13 Apr 2020 15:27:30 +0200 (CEST)
Date:   Mon, 13 Apr 2020 15:27:30 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Yan Zhao <yan.y.zhao@intel.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>, Felipe Balbi <balbi@kernel.org>,
        amd-gfx@lists.freedesktop.org,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        linux-usb@vger.kernel.org, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        virtualization@lists.linux-foundation.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
        intel-gfx@lists.freedesktop.org,
        Alex Deucher <alexander.deucher@amd.com>,
        intel-gvt-dev@lists.freedesktop.org,
        Jason Wang <jasowang@redhat.com>,
        Zhi Wang <zhi.a.wang@intel.com>
Subject: Re: [PATCH 2/6] i915/gvt/kvm: a NULL ->mm does not mean a thread
 is a kthread
Message-ID: <20200413132730.GB14455@lst.de>
References: <20200404094101.672954-1-hch@lst.de> <20200404094101.672954-3-hch@lst.de> <20200407030845.GA10586@joy-OptiPlex-7040>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200407030845.GA10586@joy-OptiPlex-7040>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: io-uring-owner@vger.kernel.org
Precedence: bulk
List-ID: <io-uring.vger.kernel.org>
X-Mailing-List: io-uring@vger.kernel.org

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.