Re: [PATCH V2 3/5] KVM/VMX: Add identical ept table pointer check

[Tianyu Lan <Tianyu.Lan@microsoft.com>]

On 7/18/2018 7:59 PM, Paolo Bonzini wrote:
> On 09/07/2018 11:02, Tianyu Lan wrote:
>> +static void check_ept_pointer(struct kvm_vcpu *vcpu, u64 eptp)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +	u64 tmp_eptp = INVALID_PAGE;
>> +	int i;
>> +
>> +	if (!kvm_x86_ops->tlb_remote_flush)
>> +		return;
>> +
>> +	spin_lock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>> +	to_vmx(vcpu)->ept_pointer = eptp;
>> +
>> +	kvm_for_each_vcpu(i, vcpu, kvm) {
>> +		if (!VALID_PAGE(tmp_eptp)) {
>> +			tmp_eptp = to_vmx(vcpu)->ept_pointer;
>> +		} else if (tmp_eptp != to_vmx(vcpu)->ept_pointer) {
>> +			to_kvm_vmx(kvm)->ept_pointers_match = false;
>> +			spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>> +			return;
>> +		}
>> +	}
>> +
>> +	to_kvm_vmx(kvm)->ept_pointers_match = true;
>> +	spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>> +}
>> +
> 
> Is there any reason to do the check here, rather than the first time the
> TLB flush is invoked?  You could:
> 
> - have a tristate (true, false, check) value for ept_pointers_match
> 
> - reset it to "check" in vmx_set_cr3
> 
> - set it to either true or false in tlb_remote_flush if it is check, and
> do the hypercall if it is true.
> 

Thanks for your suggestion. Will update.

> Paolo
>