Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752892AbaKQOnz (ORCPT ); Mon, 17 Nov 2014 09:43:55 -0500 Received: from smtp.citrix.com ([66.165.176.89]:2158 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752174AbaKQOnx (ORCPT ); Mon, 17 Nov 2014 09:43:53 -0500 X-IronPort-AV: E=Sophos;i="5.07,403,1413244800"; d="scan'208";a="192058712" Message-ID: <546A09A2.9090704@citrix.com> Date: Mon, 17 Nov 2014 14:43:46 +0000 From: David Vrabel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.5.0 MIME-Version: 1.0 To: Stefano Stabellini , CC: , , , , , , , , Ian Campbell , , , , , , , , , David Vrabel , , , Subject: Re: [Xen-devel] [RFC] add a struct page* parameter to dma_map_ops.unmap_page References: In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/11/14 14:11, Stefano Stabellini wrote: > Hi all, > I am writing this email to ask for your advice. > > On architectures where dma addresses are different from physical > addresses, it can be difficult to retrieve the physical address of a > page from its dma address. > > Specifically this is the case for Xen on arm and arm64 but I think that > other architectures might have the same issue. > > Knowing the physical address is necessary to be able to issue any > required cache maintenance operations when unmap_page, > sync_single_for_cpu and sync_single_for_device are called. > > Adding a struct page* parameter to unmap_page, sync_single_for_cpu and > sync_single_for_device would make Linux dma handling on Xen on arm and > arm64 much easier and quicker. Using an opaque handle instead of struct page * would be more beneficial for the Intel IOMMU driver. e.g., typedef dma_addr_t dma_handle_t; dma_handle_t dma_map_single(struct device *dev, void *va, size_t size, enum dma_data_direction dir); void dma_unmap_single(struct device *dev, dma_handle_t handle, size_t size, enum dma_data_direction dir); etc. Drivers would then use: dma_addr_t dma_addr(dma_handle_t handle); To obtain the bus address from the handle. > I think that other drivers have similar problems, such as the Intel > IOMMU driver having to call find_iova and walking down an rbtree to get > the physical address in its implementation of unmap_page. > > Callers have the struct page* in their hands already from the previous > map_page call so it shouldn't be an issue for them. A problem does > exist however: there are about 280 callers of dma_unmap_page and > pci_unmap_page. We have even more callers of the dma_sync_single_for_* > functions. You will also need to fix dma_unmap_single() and pci_unmap_single() (another 1000+ callers). You may need to consider a parallel set of map/unmap API calls that return/accept a handle, and then converting drivers one-by-one as required, instead of trying to convert every single driver at once. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/