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Message-ID: <4d46020f-f33a-474c-b791-be11c2ce2aa6@linux.ibm.com>
Date:   Thu, 24 Nov 2022 11:27:20 +0100
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Subject: Re: [PATCH] KVM: s390: vsie: Fix the initialization of the epoch
 extension (epdx) field
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To:     Thomas Huth <thuth@redhat.com>, kvm@vger.kernel.org,
        Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        "Collin L. Walling" <walling@linux.ibm.com>,
        Jason J Herne <jjherne@linux.ibm.com>
References: <20221123090833.292938-1-thuth@redhat.com>
From:   Janosch Frank <frankja@linux.ibm.com>
In-Reply-To: <20221123090833.292938-1-thuth@redhat.com>
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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.