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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AB566C30653 for ; Thu, 4 Jul 2024 07:49:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=TOWEFNPLCPH2NjVWmElBI7VnpkJseOiXr3UYCCHK9eY=; b=V4VEKxgxt5B70N3b0yICdN2qXy uUFePjXdGHDr8dIjz4rjoC/qOmo59rBshqXCttJfJ2FILBTWK9OaG1twPVtY2KQLxR+yKHMHpC9uF zCXhncfkip2M9QJm1fOIVWaUWwAkYsxtFeVYvbxN3Put6Lepv3AZZBcI70KvmhB0/3XR6PrsxAysj L7lnDmvUafCohkmyVWM6Ii3wKuAZA6/UDKfMNBte4rp7prdBYdHWBQskb018Dh3mGYeCvaxxDsiw0 9itcMFe2BUQyQ54+7X4R3kUYIUZJXko5nEBZhFsY1Q1Qyl9Gmb7U8WxK0W6EMGtFsjmkfwUhUrsQG zxPhDnTw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sPHDJ-0000000CURM-0GyL; Thu, 04 Jul 2024 07:49:09 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sPHDF-0000000CUQN-1Lq0 for linux-nvme@lists.infradead.org; Thu, 04 Jul 2024 07:49:07 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 52B5468AA6; Thu, 4 Jul 2024 09:48:56 +0200 (CEST) Date: Thu, 4 Jul 2024 09:48:56 +0200 From: Christoph Hellwig To: Leon Romanovsky Cc: Christoph Hellwig , Jens Axboe , Jason Gunthorpe , Robin Murphy , Joerg Roedel , Will Deacon , Keith Busch , "Zeng, Oak" , Chaitanya Kulkarni , Sagi Grimberg , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , Marek Szyprowski , =?iso-8859-1?B?Suly9G1l?= Glisse , Andrew Morton , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v1 00/18] Provide a new two step DMA API mapping API Message-ID: <20240704074855.GA26913@lst.de> References: <20240703054238.GA25366@lst.de> <20240703105253.GA95824@unreal> <20240703143530.GA30857@lst.de> <20240703155114.GB95824@unreal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240703155114.GB95824@unreal> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240704_004905_530783_FB118410 X-CRM114-Status: GOOD ( 20.72 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Wed, Jul 03, 2024 at 06:51:14PM +0300, Leon Romanovsky wrote: > If we put aside this issue, do you think that the proposed API is the right one? I haven't look at it in detail yet, but from a quick look there is a few things to note: 1) The amount of code needed in nvme worries me a bit. Now NVMe a messy driver due to the stupid PRPs vs just using SGLs, but needing a fair amount of extra boilerplate code in drivers is a bit of a warning sign. I plan to look into this to see if I can help on improving it, but for that I need a working version first. 2) The amount of seemingly unrelated global headers pulled into other global headers. Some of this might just be sloppiness, e.g. I can't see why dma-mapping.h would actually need iommu.h to start with, but pci.h in dma-map-ops.h is a no-go. 3) which brings me to real layering violations. dev_is_untrusted and dev_use_swiotlb are DMA API internals, no way I'd ever want to expose them. dma-map-ops.h is a semi-internal header only for implementations of the dma ops (as very clearly documented at the top of that file), it must not be included by drivers. Same for swiotlb.h. Not quite as concerning, but doing an indirect call for each map through dma_map_ops in addition to the iommu ops is not every efficient. We've through for a while to allow direct calls to dma-iommu similar how we do direct calls to dma-direct from the core mapping.c code. This might be a good time to do that as a prep step for this work.