Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753998AbdDKMnf (ORCPT ); Tue, 11 Apr 2017 08:43:35 -0400 Received: from foss.arm.com ([217.140.101.70]:60398 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753110AbdDKMnc (ORCPT ); Tue, 11 Apr 2017 08:43:32 -0400 Subject: Re: "Consolidate get_dma_ops" breaks Xen on ARM To: Bart Van Assche , Stefano Stabellini References: Cc: "boris.ostrovsky@oracle.com" , "jgross@suse.com" , "benh@kernel.crashing.org" , "dwmw2@infradead.org" , "hpa@zytor.com" , "mingo@redhat.com" , "linux@armlinux.org.uk" , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , linux-arm-kernel@lists.infradead.org From: Julien Grall Message-ID: Date: Tue, 11 Apr 2017 13:43:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2012 Lines: 52 Hi Bart, On 11/04/17 02:14, Bart Van Assche wrote: > On 04/10/17 17:31, Stefano Stabellini wrote: >> I think the reason is that, as you can see, if (dev && dev->dma_ops), >> dev->dma_ops is returned, while before this changes, xen_dma_ops was >> returned on Xen on ARM. >> >> Unfortunately DMA cannot work properly without using the appropriate >> xen_dma_ops. See drivers/xen/swiotlb-xen.c and arch/arm/xen/mm.c for >> more details. (The problem is easy to spot, but I wasn't CC'ed on the >> patch.) >> >> I don't know how to solve this problem without introducing some sort of >> if (xen()) in include/linux/dma-mapping.h. > > Sorry but I don't have access to an ARM development system. Does your > comment apply to dev == NULL only, dev != NULL only or perhaps to both? > If your comment applies to dev != NULL only, can you check whether > adding something like set_dma_ops(dev, get_arch_dma_ops(NULL)) to the > appropriate ARM arch_setup_dma_ops() function is sufficient? If I understand correctly, set_dma_ops will replace dev->dma_ops with Xen DMA ops. However, Xen DMA ops will need in some places to call the device specific DMA ops (see __generic_dma_ops(...)). So I think replacing dev->dma_ops is not a solution here. The hackish patch below is fixing the problem for both ARM64 and ARM32. diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 0977317c6835..43a73ddeec7a 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -174,6 +174,8 @@ int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma, #include static inline const struct dma_map_ops *get_dma_ops(struct device *dev) { + if (xen_initial_domain()) + return xen_dma_ops; if (dev && dev->dma_ops) return dev->dma_ops; return get_arch_dma_ops(dev ? dev->bus : NULL); It is not nice as this is common code, but I can't find a better solution so far. Any opinions? Cheers, -- Julien Grall