Re: [PATCH RESEND v4 8/9] KVM: MMU: Enable Lazy mode SPPT setup

Yang Weijiang
2019-09-11T00:22:59Z

On Mon, Sep 09, 2019 at 07:10:22PM +0200, Paolo Bonzini wrote:
> On 04/09/19 15:49, Yang Weijiang wrote:
> >>> This would not enable SPP if the guest is backed by huge pages.
> >>> Instead, either the PT_PAGE_TABLE_LEVEL level must be forced for all
> >>> pages covered by SPP ranges, or (better) kvm_enable_spp_protection must
> >>> be able to cover multiple pages at once.
> >>>
> >>> Paolo
> >> OK, I'll figure out how to make it, thanks!
> > Hi, Paolo,
> > Regarding this change, I have some concerns, splitting EPT huge page
> > entries(e.g., 1GB page)will take long time compared with normal EPT page
> > fault processing, especially for multiple vcpus/pages,so the in-flight time increases,
> > but HW walks EPT for translations in the meantime, would it bring any side effect?
> > or there's a way to mitigate it?
>
> Sub-page permissions are only defined on EPT PTEs, not on large pages.
> Therefore, in order to allow subpage permissions the EPT page tables
> must already be split.
>
> Paolo
Thanks, I've added code to handle hugepage, will be included in
next version patch.