Re: [PATCH] KVM: s390: vsie: Fix the initialization of the epoch extension (epdx) field

[Thomas Huth]

On 24/11/2022 11.27, Janosch Frank wrote:
> On 11/23/22 10:08, Thomas Huth wrote:
> > We recently experienced some weird huge time jumps in nested guests when
> > rebooting them in certain cases. After adding some debug code to the epoch
> > handling in vsie.c (thanks to David Hildenbrand for the idea!), it was
> > obvious that the "epdx" field (the multi-epoch extension) did not get set
> > to 0xff in case the "epoch" field was negative.
> > Seems like the code misses to copy the value from the epdx field from
> > the guest to the shadow control block. By doing so, the weird time
> > jumps are gone in our scenarios.
> >
> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=2140899
> > Fixes: 8fa1696ea781 ("KVM: s390: Multiple Epoch Facility support")
> > Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
>
> Could you please add a test for this to the KVM unit tests?
> I'd guess you might already have some code for it from your debugging sessions.

I don't have some test code for this yet - I was only testing with the 
scenario that is described in the bugzilla ticket. But sure, I can have a 
try to come up with a k-u-t test.

 Thomas