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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jan 09, 2018 at 09:23:03AM -0800, Anthony Liguori wrote:
> On Tue, Jan 9, 2018 at 8:52 AM, Stefano Stabellini
> <sstabellini@xxxxxxxxxx> wrote:
> > 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.
> 
> Can people be a bit more explicit about what they think should be done here?
> 
> I'm happy to redirect effort to PVH shim if that's what the solution
> is going to be.
> 
> I obviously prefer the HVM approach as it works on a broad range of Xen 
> versions
> without modification but I'm keen to get something done quickly and
> don't want to
> waste effort.
> 

Ian, George, Roger and I had discussions yesterday and today to see what
we can do in the short term and we think the HVM approach is very
attractive. And we certainly appreciate your effort and willing to help.

After going through the PV in PVH work we thought it should work in HVM
mode the same way as it does in PVH. So today we tested our PV in PVH
branch, which booted fine in an HVM guest (turned out only one small fix
is needed!), and everything which worked under PVH mode works in HVM
mode as well.

So basically we've been working on your idea of running PV in HVM the
whole day -- to make it work with our branch, to provide sidecar
generation mechanism.

Ian has been busy writing the sidecar script and Roger and I have been
working on cleaning up the branch.  We want to post a new version as
soon as possible (tomorrow or even tonight).

All in all: yes, we like the idea  and we're working on it. Code-wise,
we start from the PV in PVH branch because it is more functionally
complete.  I want to take in some of the code from Amazon later when
necessary (for example I like the ECS_PROXY state but haven't had time
to think deeply about it). The final shim is going to be able to run in
HVM and PVH.  When running in HVM, users need to use the sidecar
mechanism, and this is only the short term solution. The same shim is
going to be able to run in PVH, so user can smoothly upgrade to a new
PVH capable version of Xen when required.

Ian, George and Roger please correct me if I'm wrong.

Anthony, you are welcome to join #xendevel to have a quick chat about
your ideas / concerns / whatever. It is far easy to grab our attention
there. :-)

Wei.

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