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

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.


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