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

[Rich Persaud <persaur@xxxxxxxxx>]

>> On Jan 9, 2018, at 12:56, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
>> 
>> On Tue, 9 Jan 2018, Doug Goldstein wrote:
>> On 1/9/18 11:33 AM, Jan Beulich wrote:
>>>>>> 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
>> 
>> I feel like I should state the obvious here. Its tested over a large
>> data set.
> 
> Right: if we are going to commit something unpolished and unreviewed,
> let it be at least very well tested by the submitter. Honest question:
> how much more dev&test we need on PVShim before we get it to similar
> levels of confidence?

Since the primary audience for security fixes are production deployments of Xen 
where customer assets are at risk, is there an estimate for the percentage/size 
of Xen deployments where PVH (not only Xen 4.10) has already been deployed for 
production customers?  That could give other customers more confidence in 
deploying PVH in production.

Rich
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