[PATCH libvirt v1 0/6] Fix ZPCI address auto-generation on s390

[Daniel P. Berrangé]

On Tue, May 12, 2020 at 12:13:22PM +0200, Boris Fiuczynski wrote:
> On 5/7/20 5:51 PM, Laine Stump wrote:
> > In any case, it sounds like current behavior for zPCI is broken for some
> > use cases, and imo this is new enough and usage is narrow enough that if
> > the maintainers (who I would guess represent the actual users) think
> > fixing the bug is more important than 100% backward compatibility in a
> > corner case, then they should be able to change it.
> 
> I would like to get this fixed such that the behavior is architecture
> compliant.
> The behavior change would be
> Current code:
>  uid=0 fid=0 -> uid=0 fid=0 -> address gets autogenerated
>  uid=0 fid=x -> uid=0 fid=x -> address is rejected as invalid
>  uid=0       -> uid=0 fid=0 -> address gets autogenerated

IIUC, in the two cases here where the address gets auto-generated,
the resulting guest VM successfully boots & runs....

> With the series applied
>  uid=0 fid=0 -> uid=0 fid=0 -> address is rejected as invalid
>  uid=0 fid=x -> uid=0 fid=x -> address is rejected as invalid
>  uid=0       -> uid=0 fid=0 -> address is rejected as invalid

...so this proposed change is a functional regression for the
user.

> The documentation already specifies the uid value range correctly.
> The fix for users hitting the two scenarios (uid=0 fid=0) and (uid=0) is
> simple: Remove the zpci definition completely.

This would be taking a users' currently working VM, intentionally
breaking it, and then making the user pick up the pieces. This is
an example of a behaviour regression that libvirt promises to not
do to users.


Regards,
Daniel
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