Re: [PATCH v2 6/6] KVM: nVMX: optimize prepare_vmcs02{,_full} for Enlightened VMCS case

From: Vitaly Kuznetsov
Date: Wed Jul 25 2018 - 09:26:19 EST

Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:

> On 25/07/2018 14:50, Vitaly Kuznetsov wrote:
>>> But is L0 allowed to write to hv_clean_fields?
>> It is kinda expected to: currently I reset it in vmx_vcpu_run() and (if
>> I remember correctly) L1 Hyper-V only clears bits in this mask when it
>> touches certain fields so if we don't set it to 'all clean' it stays
>> zeroed forever.
> Oh, good. I didn't understand it was bidirectional.
> So nothing stops us from doing
>> if (hv_evmcs && vmx->nested.dirty_vmcs12)
>> hv_evmcs->hv_clean_fields &=
>> in prepare_vmcs02() I guess.
> In prepare_vmcs02, or rather in the enlightened VMPTRLD?

Doing it in nested_vmx_handle_enlightened_vmptrld() is even better: we
can simplify copy_enlightened_to_vmcs12() too!

The other place where we set dirty_vmcs12 is the newly introduced
vmx_set_nested_state() but I think I'm going to add support for eVMCS
there later and just return something like -ENOTSUPP for now. Too many
people work on nested simultaneously :-)