Re: [PATCH xen-4.6] xen: Remove CONFIG_X86_SUPERVISOR_MODE_KERNEL as x86_32 builds are unsupported

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2015-01-05 at 16:07 +0000, Andrew Cooper wrote:
> >> What usecase was supervisor_mode_kernel developed for?  It seems
> >> counter-intuitive, but I can't find anything in the history explaining
> >> its use.
> > It was a prototype from the pre-pvops days to see if it would be
> > feasible to have a single kernel binary which ran either on Xen or on a
> > stub hypervisor which ran it "as native" with little or no loss of
> > performance^TM (e.g. for distro's convenience to avoid the multiple
> > kernel issue).
> >
> > It never went beyond a prototype with Xen proper instead of the proposed
> > stub hypervisor and then pvops came along and was a much more sensible
> > idea...
> 
> Considering the implications of running dom0 in ring0, pvops seems like
> a much more sensible idea.

It wouldn't have been a dom0, it would have just been a native system
which happened to use some Xen interfaces, the intention was never to be
able to run guests or anything, just to allow distros to only support
one binary.

Ian.