[PATCH] xen: introduce xen_vring_use_dma

[Peng Fan]

> Subject: RE: [PATCH] xen: introduce xen_vring_use_dma
> 
> 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?

The stack trace you pasted is rpmsg issue.

> If it is the stack trace for RPMesg, can you also post the Trusty stack trace? Or
> are they indentical?

There is no stack dump here. It successfully using swiotlb to do a map,
but we actually no need swiotlb in domu to do the map.

Thanks,
Peng.