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Re: [Xen-devel] [PATCH RFC 00/10] x86 passthrough code cleanup

On Fri, Feb 23, 2018 at 05:12:05AM +0000, Tian, Kevin wrote:
> > From: Wei Liu
> > Sent: Thursday, February 22, 2018 5:47 AM
> > 
> > Hi all
> > 
> > At some point I would like to make CONFIG_HVM and CONFIG_PV work.
> > The
> > passthrough code is one of the road blocks for that work.
> Can you elaborate the motivation of this change? why does someone
> want to disable HVM or PV logic completely from hypervisor?

At some point in the future, we would like to utilise as many hardware
features as possible and have an HVM / PVH only setup. At that point PV
code will be necessarily and should be preferably compiled out to reduce
code size and attack surface.

Having PV compiled out also enable Xen to reclaim some address space
from the PV ABI.

But, we understand that PV is here to stay for at least a while and
could be useful for some other niche use cases, so upstream have
developed a PV-in-PVH shim to continue to support PV guests. The shim is
actually yet another configuration of Xen running as a PVH guest but
exposes PV ABI to PV guests. We want to disable HVM code in that case,
again, to reduce code size and attach surface.

There is also the long term benefit to make Xen more maintainable and
approachable in the future.



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