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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.01.18 at 18:23, <anthony@xxxxxxxxxxxxx> 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.

From what I've read today, I have no reason to believe the PVH
shim won't work in HVM mode. How would the HVM-only approach
be better in that case?

Jan


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