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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 4FE5AC4742C for ; Wed, 4 Nov 2020 15:56:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E802322280 for ; Wed, 4 Nov 2020 15:56:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="AUuOlw0K" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731081AbgKDPxF (ORCPT ); Wed, 4 Nov 2020 10:53:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731049AbgKDPw6 (ORCPT ); Wed, 4 Nov 2020 10:52:58 -0500 Received: from mail-qv1-xf41.google.com (mail-qv1-xf41.google.com [IPv6:2607:f8b0:4864:20::f41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7819DC0613D4 for ; Wed, 4 Nov 2020 07:52:57 -0800 (PST) Received: by mail-qv1-xf41.google.com with SMTP id da2so7909799qvb.0 for ; Wed, 04 Nov 2020 07:52:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Ep7j19TFsqDMxPD3eWS2/2sPns1mbbjfPZKNVE69Xzw=; b=AUuOlw0KLAwiVQOesE52nchcwhD+3eTZAOQ2AgXJOWJ3XMaOIef+M5UvRSDII07R0g LA67cShD36nAgQV8XflNylXVuiA9sN1sxapH5hcvQBg8BMC7oJSDqlj0n+QWuYrsrnUO eYTDqWcZiNmGe8ZSYPR7o+mtkhMR+Am5r4Q5ogWcrniQAQcqWctDeHsw4sQs+XVqbj9W uy62bb+5tgNsFxaIO8R99eExOitp2+auF/LVKl/FJMf9gQLPgmbI+98DbDFpME61i+zO jScwkquASavS/MyIkGqJ+gnyoRkmEoldBWapXzelMv/l/RVZ2eoDAumCUlXO8B4T2AnK N0wg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Ep7j19TFsqDMxPD3eWS2/2sPns1mbbjfPZKNVE69Xzw=; b=DFKQ7Isc93GVzLURhkUemcU6oUScJr6aiA6AcBRaACTX4xBy+Vm5Qk8GYy2SUasDYW isPEtRpLwBIG3tsmXxFiiHZJPbbOeo+Bs+AXKfb5v7p0v8I2D8UKdCYv5MqpVUofxqxp EvBRXJBzQp+rFQcYr1lUcbiUP1hhwS35bumFM6FE9FSHsyGZnRyjdlmNyIeAajlSxQ8A wVMa35qztdAouQjQRSUoWX5meRKQ9iLMhUZAzRV4TlDiS0kEQqW5fJXrDQ/mC9KAGsnI /oTUIznR0tQ61YEdRbzgtznvktcHnlPSWQGwFjmeHbHO7IqztbkCiwL1IS3hu9hQEu8e YfLA== X-Gm-Message-State: AOAM531XjRvEY1MuuaCUJrDS9RkynC5Sk8LN9Sv4PwugGtxrhhZW+D2F jIsoDr20V6x/6hySB3NLkTSL3w== X-Google-Smtp-Source: ABdhPJzi13d279sLLPCgu3bz4PAOPkGt+vfZ6Vorvp9mdCFZYQThEQ6fs7tjNSin4TOsVJDc3qddIA== X-Received: by 2002:a0c:d68d:: with SMTP id k13mr444150qvi.62.1604505176734; Wed, 04 Nov 2020 07:52:56 -0800 (PST) Received: from ziepe.ca (hlfxns017vw-156-34-48-30.dhcp-dynamic.fibreop.ns.bellaliant.net. [156.34.48.30]) by smtp.gmail.com with ESMTPSA id w25sm2821725qkj.85.2020.11.04.07.52.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2020 07:52:55 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kaL5j-00GY3P-95; Wed, 04 Nov 2020 11:52:55 -0400 Date: Wed, 4 Nov 2020 11:52:55 -0400 From: Jason Gunthorpe To: Christoph Hellwig Cc: 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: <20201104155255.GR36674@ziepe.ca> References: <20201104095052.1222754-1-hch@lst.de> <20201104095052.1222754-3-hch@lst.de> <20201104134241.GP36674@ziepe.ca> <20201104140108.GA5674@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201104140108.GA5674@lst.de> Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Wed, Nov 04, 2020 at 03:01:08PM +0100, Christoph Hellwig wrote: > > 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; > }; Gah, right, this is all about local_dma_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. It could work, I think a resonable ULP API would be to have some rdma_fill_ib_sge_from_sgl() rdma_map_sge_single() etc etc ie instead of wrappering the DMA API as-is we have a new API that directly builds the ib_sge. It always fills the local_dma_lkey from the pd, so it knows it is doing DMA from local kernel memory. Logically SW devices then have a local_dma_lkey MR that has an IOVA of the CPU physical address space, not the DMA address space as HW devices have. The ib_sge builders can know this detail and fill in addr from either a cpu phyical or a dma map. The SW device has to translate the addr/length in CPU space to something else. It actually makes reasonable sense architecturally. This is actually much less horrible than I thought.. Convert all ULPs to one of these new APIs, searching for local_dma_lkey will find all places. This will replace a whole lot of calls to ib DMA API wrapper functions. Searching for local_dma_lkey will find all users. Drivers already work with sge.addr == CPU address, so no driver change Then to kill the dma_ops wrappers the remaining users should all be connected to map_mr_sg. In this case we want a no-op dma map and fix the three map_mr_sg's to use the page side of the sgl, not the DMA side Not as horrible as I imagined at first, actually.. Jason