Re: [PATCH] KVM/VMX: Check ept_pointer before flushing ept tlb

Vitaly Kuznetsov
2018-11-07T10:49:11Z

Tianyu Lan <ltykernel@gmail.com> writes:

> Hi Vitaly:
> Thanks for your review.
>
> On 11/6/2018 11:50 PM, Vitaly Kuznetsov wrote:
>> ltykernel@gmail.com writes:
>>
>>> From: Lan Tianyu <Tianyu.Lan@microsoft.com>
>>>
>>> This patch is to initialize ept_pointer to INVALID_PAGE and check it
>>> before flushing ept tlb. If ept_pointer is invalidated, bypass the flush
>>> request.
>>>
>>
>> To be honest I fail to understand the reason behind the patch: instead
>> of doing one unneeded flush request with ept_pointer==0 (after vCPU is
>> initialized) we now do the check every time. Could you please elaborate
>> on why this is needed?
>
> The reason to introduce the check here is to avoid flushing ept tlb
> without valid ept table. When nested guest boots up and only BP is
> active, we should not do flush for APs and L1 hypervisor hasn't set
> valid EPT table for APs.

Yes, I understand that but I'm trying to avoid additional checks on
hotpath as during normal operation EPT pointer is always set.

Could we just initialize ept_pointers_match to something like
EPT_POINTERS_NOTSET and achive the same result?

--
Vitaly