linux-kernel - Re: [RFC] virtio_ring: check dma_mem for xen

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Date:   Mon, 21 Jan 2019 21:36:39 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     "hch@...radead.org" <hch@...radead.org>
Cc:     Peng Fan <peng.fan@....com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-remoteproc@...r.kernel.org" <linux-remoteproc@...r.kernel.org>
Subject: Re: [RFC] virtio_ring: check dma_mem for xen_domain

On Mon, Jan 21, 2019 at 12:28:30AM -0800, hch@...radead.org wrote:
> On Mon, Jan 21, 2019 at 04:51:57AM +0000, Peng Fan wrote:
> > on i.MX8QM, M4_1 is communicating with DomU using rpmsg with a fixed
> > address as the dma mem buffer which is predefined.
> > 
> > Without this patch, the flow is:
> > vring_map_one_sg -> vring_use_dma_api
> >                  -> dma_map_page
> > 		       -> __swiotlb_map_page
> > 		                ->swiotlb_map_page
> > 				->__dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
> > However we are using per device dma area for rpmsg, phys_to_virt
> > could not return a correct virtual address for virtual address in
> > vmalloc area. Then kernel panic.
> 
> And that is the right thing to do.  You must not call dma_map_* on
> memory that was allocated from dma_alloc_*.
> 
> We actually have another thread which appears to be for this same issue.

Sorry, which thread do you refer to?

-- 
MST