From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:43950 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726259AbfAXUe2 (ORCPT ); Thu, 24 Jan 2019 15:34:28 -0500 Date: Thu, 24 Jan 2019 15:34:25 -0500 From: "Michael S. Tsirkin" Subject: Re: [Xen-devel] [RFC] virtio_ring: check dma_mem for xen_domain Message-ID: <20190124145849-mutt-send-email-mst@kernel.org> References: <20190121050056.14325-1-peng.fan@nxp.com> <20190123071232.GA20526@infradead.org> <20190123211405.GA4971@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-remoteproc-owner@vger.kernel.org To: Stefano Stabellini Cc: Peng Fan , "hch@infradead.org" , "jasowang@redhat.com" , "xen-devel@lists.xenproject.org" , "linux-remoteproc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "luto@kernel.org" , "jgross@suse.com" , "boris.ostrovsky@oracle.com" , "bjorn.andersson@linaro.org" , "jliang@xilinx.com" List-ID: On Thu, Jan 24, 2019 at 11:14:53AM -0800, Stefano Stabellini wrote: > On Thu, 24 Jan 2019, Peng Fan wrote: > > Hi stefano, > > > > > -----Original Message----- > > > From: Stefano Stabellini [mailto:sstabellini@kernel.org] > > > Sent: 2019年1月24日 7:44 > > > To: hch@infradead.org > > > Cc: Stefano Stabellini ; Peng Fan > > > ; mst@redhat.com; jasowang@redhat.com; > > > xen-devel@lists.xenproject.org; linux-remoteproc@vger.kernel.org; > > > linux-kernel@vger.kernel.org; virtualization@lists.linux-foundation.org; > > > luto@kernel.org; jgross@suse.com; boris.ostrovsky@oracle.com; > > > bjorn.andersson@linaro.org; jliang@xilinx.com > > > Subject: Re: [Xen-devel] [RFC] virtio_ring: check dma_mem for xen_domain > > > > > > On Wed, 23 Jan 2019, hch@infradead.org wrote: > > > > On Wed, Jan 23, 2019 at 01:04:33PM -0800, Stefano Stabellini wrote: > > > > > If vring_use_dma_api is actually supposed to return true when > > > > > dma_dev->dma_mem is set, then both Peng's patch and the patch I > > > > > wrote are not fixing the real issue here. > > > > > > > > > > I don't know enough about remoteproc to know where the problem > > > > > actually lies though. > > > > > > > > The problem is the following: > > > > > > > > Devices can declare a specific memory region that they want to use > > > > when the driver calls dma_alloc_coherent for the device, this is done > > > > using the shared-dma-pool DT attribute, which comes in two variants > > > > that would be a little to much to explain here. > > > > > > > > remoteproc makes use of that because apparently the device can only > > > > communicate using that region. But it then feeds back memory obtained > > > > with dma_alloc_coherent into the virtio code. For that it calls > > > > vmalloc_to_page on the dma_alloc_coherent, which is a huge no-go for > > > > the ĐMA API and only worked accidentally on a few platform, and > > > > apparently arm64 just changed a few internals that made it stop > > > > working for remoteproc. > > > > > > > > The right answer is to not use the DMA API to allocate memory from a > > > > device-speficic region, but to tie the driver directly into the DT > > > > reserved memory API in a way that allows it to easilt obtain a struct > > > > device for it. > > > > > > If I understand correctly, Peng should be able to reproduce the problem on > > > native Linux without any Xen involvement simply by forcing > > > vring_use_dma_api to return true. Peng, can you confirm? > > > > It is another issue without xen involvement, > > There is an thread talking this: https://patchwork.kernel.org/patch/10742923/ > > > > Without xen, vring_use_dma_api will return false. > > With xen, if vring_use_dma_api returns true, it will dma_map_xx and trigger dump. > > It is true that for Xen on ARM DomUs it is not necessary today to return > true from vring_use_dma_api. However, returning true from > vring_use_dma_api should not break Linux. When the rpmesg issue is > fixed, this problem should also go away without any need for additional > changes on the xen side I think. Let less systems bypass the standard virtio logic (using feature bit to figure out bypassing DMA API), the better.