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

[Thomas Huth <thuth@redhat.com>]

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@redhat.com>
> 
> 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