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

[Doug Goldstein <cardoe@xxxxxxxxxx>]

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.
-- 
Doug Goldstein

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