KVM: s390: Fix fault-in code

KVM: s390: Fix fault-in code

Fix the fault-in code so that it does not return success if a
concurrent unmap event invalidated the fault-in process between the
best-effort lockless check and the proper check with lock.

The new behaviour is to retry, like the best-effort lockless check
already did.

This prevents the fault-in handler from returning success without
having actually faulted in the requested page.

Fixes: e907ae530133 ("KVM: s390: Add helper functions for fault handling")
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260602142356.169458-7-imbrenda@linux.ibm.com>