So I found (and could verify) that it is actually this change from 3.10 which fixes nested for L1 guests >=3.15:
commit 33fb20c39e98b90813b5ab2d9a0d6faa6300caca Author: Jan Kiszka <email address hidden> Date: Wed Mar 6 15:44:03 2013 +0100
KVM: nVMX: Fix content of MSR_IA32_VMX_ENTRY/EXIT_CTLS
And that change looks not too intrusive and to be rather a fix than adding any feature. It also cleanly cherry-picks into 3.2.
So I found (and could verify) that it is actually this change from 3.10 which fixes nested for L1 guests >=3.15:
commit 33fb20c39e98b90 813b5ab2d9a0d6f aa6300caca
Author: Jan Kiszka <email address hidden>
Date: Wed Mar 6 15:44:03 2013 +0100
KVM: nVMX: Fix content of MSR_IA32_ VMX_ENTRY/ EXIT_CTLS
And that change looks not too intrusive and to be rather a fix than adding any feature. It also cleanly cherry-picks into 3.2.