[PATCH] xen: introduce xen_vring_use_dma

[Stefano Stabellini]

On Mon, 29 Jun 2020, Peng Fan wrote:
> > > If that is the case, how is it possible that virtio breaks on ARM
> > > using the default dma_ops? The breakage is not Xen related (except
> > > that Xen turns dma_ops on). The original message from Peng was:
> > >
> > >   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.
> > >
> > > I must be missing something. Maybe it is because it has to do with RPMesg?
> > 
> > I think it's an RPMesg bug, yes
> 
> rpmsg bug is another issue, it should not use dma_alloc_coherent for reserved area,
> and use vmalloc_to_page.
> 
> Anyway here using dma api will also trigger issue.

Is the stack trace above for the RPMesg issue or for the Trusty issue?
If it is the stack trace for RPMesg, can you also post the Trusty stack
trace? Or are they indentical?