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

From: Thomas Huth
Date: Thu Nov 24 2022 - 05:47:47 EST


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