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

Vitaly Kuznetsov
2018-07-25T08:37:50Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 21/06/2018 14:30, Vitaly Kuznetsov wrote:
>> +static __always_inline bool evmcs_needs_write(struct vcpu_vmx *vmx,
>> + u16 clean_field)
>> +{
>> + if (vmx->nested.dirty_vmcs12)
>> + return true;
>
> Why is this needed? If it weren't for it, you could pass hv_evmcs
> directly to evmcs_needs_write, which would simplify the code a bit in
> the caller.

This is an equivalent of prepare_vmcs02()/prepare_vmcs02_full() split
for eVMCS case: when we switch from L2 guest A to L2 guest B we need to
write the whole VMCS so evmcs_needs_write() needs to return true.

We can, however, make an optimisation: forcefuly reset hv_clean_fields
mask on enlightened vmptrld making 'dirty_vmcs12' check redundant.

This series was posted quite some time ago, I'll rebase and re-test with
the fix included.

Thanks!

--
Vitaly