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 19F1FC54E49 for ; Tue, 5 Mar 2024 14:51:43 +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:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Rqswi7ipIoZG+INOG3X2gMd6ini0syHXXW75E+5+5wU=; b=tqD8YnnPeZCkAJfra1TALMXN25 6NmohdhNEND1+bdB8Cy22X9JOq1MuzR5Wd6M2XD5vge9RDVuuIMdPE8m6j4rerzEB9TpUyb43/v2D zo303Vchdz/96qBkZqLJYl1Ja3s5MJG46u8kLa6r4+nfKT2w8uxGcCQAxx4UdICfmyPq/bRAcsLMt E+WmWBZJhEelh0CSi2uXrVWybgfWIZS9Y3wLkAMBJ9G5esC+rnqt/Yi1DteCtfIwiLV5bihDMdnDS g/KzaIrNh7xx+DBsLlxQUvvLv3kR7muZz8nPZrYrNiO5z8mnI0WxiKae6kn+ABAtoBYimoe5uLIoB Bjbw4SWw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rhW8q-0000000E7t0-3weX; Tue, 05 Mar 2024 14:51:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rhTY9-0000000DURC-0zGb for linux-nvme@lists.infradead.org; Tue, 05 Mar 2024 12:05:38 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A49DE1FB; Tue, 5 Mar 2024 04:06:08 -0800 (PST) Received: from [10.57.67.228] (unknown [10.57.67.228]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 25B763F73F; Tue, 5 Mar 2024 04:05:25 -0800 (PST) Message-ID: <47afacda-3023-4eb7-b227-5f725c3187c2@arm.com> Date: Tue, 5 Mar 2024 12:05:23 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC RESEND 00/16] Split IOMMU DMA mapping operation to two steps To: Leon Romanovsky , Christoph Hellwig , Marek Szyprowski , Joerg Roedel , Will Deacon , Jason Gunthorpe , Chaitanya Kulkarni Cc: Jonathan Corbet , Jens Axboe , Keith Busch , Sagi Grimberg , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, kvm@vger.kernel.org, linux-mm@kvack.org, Bart Van Assche , Damien Le Moal , Amir Goldstein , "josef@toxicpanda.com" , "Martin K. Petersen" , "daniel@iogearbox.net" , Dan Williams , "jack@suse.com" , Leon Romanovsky , Zhu Yanjun References: From: Robin Murphy Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240305_040537_411668_3CA12CE5 X-CRM114-Status: GOOD ( 31.03 ) X-Mailman-Approved-At: Tue, 05 Mar 2024 05:32:59 -0800 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 2024-03-05 11:18 am, Leon Romanovsky wrote: > This is complimentary part to the proposed LSF/MM topic. > https://lore.kernel.org/linux-rdma/22df55f8-cf64-4aa8-8c0b-b556c867b926@linux.dev/T/#m85672c860539fdbbc8fe0f5ccabdc05b40269057 > > This is posted as RFC to get a feedback on proposed split, but RDMA, VFIO and > DMA patches are ready for review and inclusion, the NVMe patches are still in > progress as they require agreement on API first. > > Thanks > > ------------------------------------------------------------------------------- > The DMA mapping operation performs two steps at one same time: allocates > IOVA space and actually maps DMA pages to that space. This one shot > operation works perfectly for non-complex scenarios, where callers use > that DMA API in control path when they setup hardware. > > However in more complex scenarios, when DMA mapping is needed in data > path and especially when some sort of specific datatype is involved, > such one shot approach has its drawbacks. > > That approach pushes developers to introduce new DMA APIs for specific > datatype. For example existing scatter-gather mapping functions, or > latest Chuck's RFC series to add biovec related DMA mapping [1] and > probably struct folio will need it too. > > These advanced DMA mapping APIs are needed to calculate IOVA size to > allocate it as one chunk and some sort of offset calculations to know > which part of IOVA to map. I don't follow this part at all - at *some* point, something must know a range of memory addresses involved in a DMA transfer, so that's where it should map that range for DMA. Even in a badly-designed system where the point it's most practical to make the mapping is further out and only knows that DMA will touch some subset of a buffer, but doesn't know exactly what subset yet, you'd usually just map the whole buffer. I don't see why the DMA API would ever need to know about anything other than pages/PFNs and dma_addr_ts (yes, it does also accept them being wrapped together in scatterlists; yes, scatterlists are awful and it would be nice to replace them with a better general DMA descriptor; that is a whole other subject of its own). > Instead of teaching DMA to know these specific datatypes, let's separate > existing DMA mapping routine to two steps and give an option to advanced > callers (subsystems) perform all calculations internally in advance and > map pages later when it is needed. From a brief look, this is clearly an awkward reinvention of the IOMMU API. If IOMMU-aware drivers/subsystems want to explicitly manage IOMMU address spaces then they can and should use the IOMMU API. Perhaps there's room for some quality-of-life additions to the IOMMU API to help with common usage patterns, but the generic DMA mapping API is absolutely not the place for it. Thanks, Robin. > In this series, three users are converted and each of such conversion > presents different positive gain: > 1. RDMA simplifies and speeds up its pagefault handling for > on-demand-paging (ODP) mode. > 2. VFIO PCI live migration code saves huge chunk of memory. > 3. NVMe PCI avoids intermediate SG table manipulation and operates > directly on BIOs. > > Thanks > > [1] https://lore.kernel.org/all/169772852492.5232.17148564580779995849.stgit@klimt.1015granger.net > > Chaitanya Kulkarni (2): > block: add dma_link_range() based API > nvme-pci: use blk_rq_dma_map() for NVMe SGL > > Leon Romanovsky (14): > mm/hmm: let users to tag specific PFNs > dma-mapping: provide an interface to allocate IOVA > dma-mapping: provide callbacks to link/unlink pages to specific IOVA > iommu/dma: Provide an interface to allow preallocate IOVA > iommu/dma: Prepare map/unmap page functions to receive IOVA > iommu/dma: Implement link/unlink page callbacks > RDMA/umem: Preallocate and cache IOVA for UMEM ODP > RDMA/umem: Store ODP access mask information in PFN > RDMA/core: Separate DMA mapping to caching IOVA and page linkage > RDMA/umem: Prevent UMEM ODP creation with SWIOTLB > vfio/mlx5: Explicitly use number of pages instead of allocated length > vfio/mlx5: Rewrite create mkey flow to allow better code reuse > vfio/mlx5: Explicitly store page list > vfio/mlx5: Convert vfio to use DMA link API > > Documentation/core-api/dma-attributes.rst | 7 + > block/blk-merge.c | 156 ++++++++++++++ > drivers/infiniband/core/umem_odp.c | 219 +++++++------------ > drivers/infiniband/hw/mlx5/mlx5_ib.h | 1 + > drivers/infiniband/hw/mlx5/odp.c | 59 +++-- > drivers/iommu/dma-iommu.c | 129 ++++++++--- > drivers/nvme/host/pci.c | 220 +++++-------------- > drivers/vfio/pci/mlx5/cmd.c | 252 ++++++++++++---------- > drivers/vfio/pci/mlx5/cmd.h | 22 +- > drivers/vfio/pci/mlx5/main.c | 136 +++++------- > include/linux/blk-mq.h | 9 + > include/linux/dma-map-ops.h | 13 ++ > include/linux/dma-mapping.h | 39 ++++ > include/linux/hmm.h | 3 + > include/rdma/ib_umem_odp.h | 22 +- > include/rdma/ib_verbs.h | 54 +++++ > kernel/dma/debug.h | 2 + > kernel/dma/direct.h | 7 +- > kernel/dma/mapping.c | 91 ++++++++ > mm/hmm.c | 34 +-- > 20 files changed, 870 insertions(+), 605 deletions(-) >