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

[Janosch Frank]

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.