Re: [Xen-devel] Radical proposal: ship not-fully-tidied shim as 4.10.1

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 9 Jan 2018, George Dunlap wrote:
> On Mon, Jan 8, 2018 at 9:01 PM, Rich Persaud <persaur@xxxxxxxxx> wrote:
> > On a similarly pragmatic note: would a variation of Anthony's vixen patch 
> > series be suitable for pre-PVH Xen 4.6 - 4.9?  These versions are currently 
> > documented as security-supported (Oct 2018 - July 2020).
> 
> Hmm, Ian's mail seems to be focusing on the idea of checking in a
> non-polished series to 4.10, rather than exctly what the content of
> that series would be.
> 
> In the IRL conversation that preceeded this mail, the new short-term
> target we discussed was:
> 1. A 4.10-based shim that could boot either under HVM or PVH
> 2. A script that would take an existing PV config, and spit out a) a
> bootable ISO with the shim & whatever was needed, and b) a new config
> that would boot the same VM, but in HVM mode with the shim
> 
> The script + a 4.10 shim binary *should* allow most PV guests to boot
> without any changes whatsoever for most older versions of Xen.
> 
> There are a number of people for whom this won't work; I think we also
> need to provide a way to transparently change PV guests into PVshim
> guests.  But that will necessarily involve significant toolstack
> functionality, at which point you might as well backport PVH as well.

Yes, there will be a number of people that won't be covered by this fix,
including those that can't use HVM/PVH mode because VT-x isn't available
at all in their environment. That is the only reason to run PV today.
Providing a way to transparently change PV guests into PVshim guests
won't cover any of these cases. A more complete workaround to SP3 is
along the lines of https://marc.info/?l=xen-devel&m=151509740625690.

That said, I realize that we are only trying to do the best we can in a
very difficult situation, with very little time in our hands. I agree
with Ian that we should commit something unpolished and only partially
reviewed soon, even though it doesn't cover a good chunk of the userbase
for one reason or another. Even if migration doesn't work, it will still
help all that don't require it. It is only a partial fix by nature
anyway.

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