Re: [PATCH v2 31/32] KVM: nVMX: Don't flush TLB on nested VM transition with EPT enabled

[Paolo Bonzini]

On 17/03/20 19:22, Sean Christopherson wrote:
> On Tue, Mar 17, 2020 at 06:18:37PM +0100, Paolo Bonzini wrote:
>> On 17/03/20 05:52, Sean Christopherson wrote:
>>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>>> index d816f1366943..a77eab5b0e8a 100644
>>> --- a/arch/x86/kvm/vmx/nested.c
>>> +++ b/arch/x86/kvm/vmx/nested.c
>>> @@ -1123,7 +1123,7 @@ static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool ne
>>>  	}
>>>  
>>>  	if (!nested_ept)
>>> -		kvm_mmu_new_cr3(vcpu, cr3, false);
>>> +		kvm_mmu_new_cr3(vcpu, cr3, enable_ept);
>>
>> Even if enable_ept == false, we could have already scheduled or flushed
>> the TLB soon due to one of 1) nested_vmx_transition_tlb_flush 2)
>> vpid_sync_context in prepare_vmcs02 3) the processor doing it for
>> !enable_vpid.
>>
>> So for !enable_ept only KVM_REQ_MMU_SYNC is needed, not
>> KVM_REQ_TLB_FLUSH_CURRENT I think.  Worth adding a TODO?
> 
> Now that you point it out, I think it makes sense to unconditionally pass
> %true here, i.e. rely 100% on nested_vmx_transition_tlb_flush() to do the
> right thing.

Why doesn't it need KVM_REQ_MMU_SYNC either?  All this should be in a
comment as well, of course.

(All patches I didn't comment on look good).

Paolo