Re: [Xen-devel] [RFC PATCH v2 3/3] tools, libxl: handle the iomem parameter with the memory_mapping hcall

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-03-13 at 15:43 +0000, Jan Beulich wrote:
> >>> On 13.03.14 at 16:27, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Mon, 2014-03-10 at 09:25 +0100, Arianna Avanzini wrote:
> >> Currently, the configuration-parsing code concerning the handling of the
> >> iomem parameter only invokes the XEN_DOMCTL_iomem_permission hypercall.
> >> This commit lets the XEN_DOMCTL_memory_mapping hypercall be invoked
> >> after XEN_DOMCTL_iomem_permission when the iomem parameter is parsed
> >> from a domU configuration file, so that the address range can be mapped
> >> to the address space of the domU.
> >> NOTE: the added code is still common to both x86 and ARM; it also
> >>       implements a simple 1:1 mapping that could clash with the domU's
> >>       existing memory layout if the range is already in use in the
> >>       guest's address space.
> > 
> > In that case you need to CC the x86 maintainers (Jan, Keir, Tim) here.
> > It doesn't seem to me that this is going to be the correct thing to do
> > for either x86 PV or x86 HVM guests.
> > 
> > My gut feeling is that this should be ifdef'd or otherwise made
> > conditional.
> 
> At the very least - it really looks more like a temporary hack than
> a long term solution to me. Why would we ever want, for other
> than experimental purposes, a 1:1 address relationship baked
> into anything?

Indeed, although that's slightly secondary to whether these call make
sense at all for x86 regardless of whether they are 1:1 or not.

Ian.


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