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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 64DFAC388F7 for ; Wed, 4 Nov 2020 14:01:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 140DA205CB for ; Wed, 4 Nov 2020 14:01:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726843AbgKDOBO (ORCPT ); Wed, 4 Nov 2020 09:01:14 -0500 Received: from verein.lst.de ([213.95.11.211]:42740 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726874AbgKDOBN (ORCPT ); Wed, 4 Nov 2020 09:01:13 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 265B767373; Wed, 4 Nov 2020 15:01:09 +0100 (CET) Date: Wed, 4 Nov 2020 15:01:08 +0100 From: Christoph Hellwig To: Jason Gunthorpe Cc: Christoph Hellwig , Bjorn Helgaas , Logan Gunthorpe , linux-rdma@vger.kernel.org, linux-pci@vger.kernel.org, iommu@lists.linux-foundation.org Subject: Re: [PATCH 2/5] RDMA/core: remove use of dma_virt_ops Message-ID: <20201104140108.GA5674@lst.de> References: <20201104095052.1222754-1-hch@lst.de> <20201104095052.1222754-3-hch@lst.de> <20201104134241.GP36674@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201104134241.GP36674@ziepe.ca> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Wed, Nov 04, 2020 at 09:42:41AM -0400, Jason Gunthorpe wrote: > On Wed, Nov 04, 2020 at 10:50:49AM +0100, Christoph Hellwig wrote: > > > +int ib_dma_virt_map_sg(struct ib_device *dev, struct scatterlist *sg, int nents) > > +{ > > + struct scatterlist *s; > > + int i; > > + > > + for_each_sg(sg, s, nents, i) { > > + sg_dma_address(s) = (uintptr_t)sg_virt(s); > > + sg_dma_len(s) = s->length; > > Hmm.. There is nothing ensuring the page is mapped here for this > sg_virt(). Before maybe some of the kconfig stuff prevented highmem > systems indirectly, I wonder if we should add something more direct to > exclude highmem for these drivers? I had actually noticed this earlier as well and then completely forgot about it.. rdmavt depends on X86_64, so it can't be used with highmem, but for rxe and siw there weren't any such dependencies so I think we were just lucky. Let me send a fix to add explicit depencies and then respin this series on top of that.. > Sigh. I think the proper fix is to replace addr/length with a > scatterlist pointer in the struct ib_sge, then have SW drivers > directly use the page pointer properly. The proper fix is to move the DMA mapping into the RDMA core, yes. And as you said it will be hard. But I don't think scatterlists are the right interface. IMHO we can keep re-use the existing struct ib_sge: struct ib_ge { u64 addr; u32 length; u32 lkey; }; with the difference that if lkey is not a MR, addr is the physical address of the memory, not a dma_addr_t or virtual address.