Re: [PATCH v2] xen/arm: fix gnttab_need_iommu_mapping

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 9 Feb 2021, Ian Jackson wrote:
> Jan Beulich writes ("Re: [PATCH v2] xen/arm: fix gnttab_need_iommu_mapping"):
> > On 08.02.2021 21:24, Stefano Stabellini wrote:
> ...
> > > For these cases, I would just follow a simple rule of thumb:
> > > - is the submitter willing to provide the backport?
> > > - is the backport low-risk?
> > > - is the underlying bug important?
> > > 
> > > If the answer to all is "yes" then I'd go with it.
> > 
> > Personally I disagree, for the very simple reason of the question
> > going to become "Where do we draw the line?" The only non-security
> > backports that I consider acceptable are low-risk changes to allow
> > building with newer tool chains. I know other backports have
> > occurred in the past, and I did voice my disagreement with this
> > having happened.
> 
> I think I take a more relaxed view than Jan, but still a much more
> firm line than Stefano.  My opinion is that we should make exceptions
> for only bugs of exceptional severity.
> 
> I don't think I have seen an argument that this bug is exceptionally
> severe.
> 
> For me the fact that you can only experience this bug if you upgrade
> the hardware or significantly change the configuration, means that
> this isn't so serious a bug.

Yeah, I think that's really the core of this issue. If somebody is
already using 4.12 happily, there is really no reason for them to take
the fix. If somebody is about to use 4.12, then it is a severe issue.

The view of the group is that nobody should be switching to 4.12 now
because there are newer releases out there. I don't know if that is
true.

I didn't realize we had a policy or even a recommendation of always
choosing the latest among the many releases available with
security-support. I went through the website and SUPPORT.md but couldn't
find it spelled out anywhere. See:

https://xenproject.org/downloads/
https://xenproject.org/downloads/xen-project-archives/xen-project-4-12-series/
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=SUPPORT.md;h=52f25fa85af41fa3b38288ab7e172408b77dc779;hb=97b7b5567fba6918a656ad349051b5343b5dea2e

At most we have:

    Supported-Until: 2020-10-02
    Security-Support-Until: 2022-04-02

Anecdotally, if I go to https://www.kernel.org/ to download a kernel
tarball, I expect all tarballs to have all the major functionalities. I
wouldn't imagine that I cannot get one entire Linux subsystem (e.g.
ethernet or SATA) to work if I don't pick the latest.

Maybe it would make sense to clarify which releases are discouraged from
being used on https://xenproject.org/downloads/ at least?