Re: [Xen-devel] Please apply "partially revert "xen: Remove event channel..."

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/11/2017 05:53 AM, Andrew Cooper wrote:
> On 10/04/17 19:48, Boris Ostrovsky wrote:
> > > > The following is meant as a real question without any prejudice:
> > > >
> > > > How old a Xen version do we want to support in the Linux kernel?
> > > >
> > > > - Only those being still maintained (meaning getting security fixes)
> > Definitely not this. 4.4 is the oldest version receiving official XSA
> > patches and it's only 3 years old.
> >
> > > > - Versions max. X years after getting last security fixes (what value
> > > >   of X?)
> > > > - From version Y on (what value of Y?)
> > > > - All versions which we can think of
> > > >
> > > > I think we should answer this question in order to know what we can
> > > > remove in the Linux kernel without breaking something.
> > > Ideally, "All versions which we can think of", unless it becomes too
> > > difficult. In that case, I would switch to "From version Y" where Y is
> > > not troublesome to support (and older than the oldest supported Xen
> > > release).
> > So Oracle, for example, officially supports its virtualization product
> > for 8 to 10 years.
> >
> > Which means that 10 years after a product is released it is possible to
> > see new version of Linux on  such a product (although realistically
> > vendors may generally support more limited sets of guests).
> >
> > If we are to follow this line of reasoning Xen 3.4 needs to be supported
> > --- it was released in 2009.
> Citrix XenServer is also 10 years.
>
> From what I understand, SUSE are still supporting Xen 3.2 based
> products, which is the same kind of vintage.

I think the right thing is indeed to revert 72a9b186292 (and therefore 
da72ff5bfcb02).  Any objections?
The only possible remaining issue is that kernels not using vector 
callbacks running on post-4.0 Xen won't work. But we always use 
callbacks if they are available (and they are post 4.0).
-boris

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