From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1757532AbdKGP6Y (ORCPT <rfc822;w@1wt.eu>);
        Tue, 7 Nov 2017 10:58:24 -0500
Received: from bombadil.infradead.org ([65.50.211.133]:42401 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1752702AbdKGP6W (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 7 Nov 2017 10:58:22 -0500
Date: Tue, 7 Nov 2017 07:58:05 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Wei Hu (Xavier)" <xavier.huwei@huawei.com>,
        Robin Murphy <robin.murphy@arm.com>, Leon Romanovsky <leon@kernel.org>,
        shaobo.xu@intel.com, xavier.huwei@tom.com, lijun_nudt@163.com,
        oulijun@huawei.com, linux-rdma@vger.kernel.org,
        charles.chenxin@huawei.com, linuxarm@huawei.com,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, dledford@redhat.com, liuyixian@huawei.com,
        zhangxiping3@huawei.com, shaoboxu@tom.com
Subject: Re: [PATCH for-next 2/4] RDMA/hns: Add IOMMU enable support in hip08
Message-ID: <20171107155805.GA24082@infradead.org>
References: <1506763741-81429-1-git-send-email-xavier.huwei@huawei.com>
 <1506763741-81429-3-git-send-email-xavier.huwei@huawei.com>
 <20170930161023.GI2965@mtr-leonro.local>
 <59DF60A3.7080803@huawei.com>
 <5fe5f9b9-2c2b-ab3c-dafa-3e2add051bbb@arm.com>
 <59F97BBE.5070207@huawei.com>
 <fc7433af-4fa7-6b78-6bec-26941a427002@arm.com>
 <5A011E49.6060407@huawei.com>
 <20171107154838.GC21466@ziepe.ca>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171107154838.GC21466@ziepe.ca>
User-Agent: Mutt/1.8.3 (2017-05-23)
X-SRS-Rewrite: SMTP reverse-path rewritten from <hch@infradead.org> by bombadil.infradead.org. See http://www.infradead.org/rpr.html
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Nov 07, 2017 at 08:48:38AM -0700, Jason Gunthorpe wrote:
> Can't you just use vmalloc and dma_map that? Other drivers follow that
> approach..

You can't easily due to the flushing requirements.  We used to do that
in XFS and it led to problems.  You need the page allocator + vmap +
invalidate_kernel_vmap_range + flush_kernel_vmap_range to get the
cache flushing right.