[PATCH v7 3/8] arm64: introduce is_device_dma_coherent

[Stefano Stabellini]

On Mon, 10 Nov 2014, Stefano Stabellini wrote:
> > BTW, pfn_valid() is more expensive than simply comparing the mfn with
> > pfn for dom0. The calling code knows this already and it may be quicker
> > to simply pass a "bool foreign" argument.
> 
> Good point, I can compare mfn and pfn here.
> I cannot do the same in unmap_page and the various sync operations,
> because there is no pfn available, but maybe I could use
> set_page_private to set a flag. I'll think about it.

But of course there is no struct page either so I think pfn_valid will
have to stay in unmap and sync