Re: [PATCH] libxc: introduce a per architecture scratch pfn for temporary grant mapping

[Julien Grall <julien.grall@linaro.org>]

On 15/01/15 13:14, Andrew Cooper wrote:
> For things like grant tables, the toolstack is already capable of using
> add_to_physmap to make the pages mappable, but this is inefficient and
> possibly interferes with the guest physical layout.  I propose a short
> circuit of this which allows the toolstack to map any legitimate physmap
> spaces directly, without having to shuffle them in and out of the
> physmap. i.e. a map foreign hypercall which takes {domid, space, idx} as
> parameters rather than {domid, gfn}.
> 
> For the magic pages, this proposal creates a secondary address space,
> which is intended never for the guest to be able to map.  This can
> remove all the current "magic pages" which live in the low MMIO hole
> (ioreq, bufioreq, mem_event rings, etc), and prevents the need for
> emulation pages ever to be accessible to the guest.

If I'm not mistaken a such solution would require modification in the
kernel. So we would have to keep compatibility with older kernel.

Regards,

-- 
Julien Grall