Re: [PATCH v3 2/3] s390x/pv: Introduce a s390_pv_check() helper for runtime

[Thomas Huth]

On 17/01/2023 09.40, Janosch Frank wrote:
> On 1/16/23 18:46, Cédric Le Goater wrote:
> > From: Cédric Le Goater <clg@redhat.com>
> >
> > If a secure kernel is started in a non-protected VM, the OS will hang
> > during boot without giving a proper error message to the user.
>
> Didn't we establish that you were missing the IOMMU flag so this statement 
> isn't correct anymore?
>
>
> I haven't yet fully ingested my coffee, but from what I understand you would 
> block a switch into PV mode if cgs is not set. Which would mean that PV KVM 
> unit tests wouldn't start anymore as well as any VMs that have the unpack 
> feature but not cgs.
>
> And that's not something that we want.
>
> You can start a PV VM without cgs if unpack is in the CPU model. The ONLY 
> requirement that we should fail on is unpack.

So would it make sense to check for S390_FEAT_UNPACK (or something else?) 
here, or should the patch completely be dropped instead?

 Thomas