Re: [PATCH v3 20/34] KVM: x86: KVM_REQ_TLB_FLUSH_CURRENT is a superset of KVM_REQ_HV_TLB_FLUSH too

Sean Christopherson
2022-05-19T23:44:54Z

On Thu, May 19, 2022, Vitaly Kuznetsov wrote:
> This, however, made me think there's room for optimization here. In some
> cases, when both KVM_REQ_TLB_FLUSH_CURRENT and KVM_REQ_TLB_FLUSH_GUEST
> were requested, there's no need to flush twice, e.g. on SVM
> .flush_tlb_current == .flush_tlb_guest. I'll probably not go into this
> territory with this series as it's already fairly big, just something
> for the future.

Definitely not worth your time. On VMX, CURRENT isn't a superset of GUEST when
EPT is enabled. And on SVM, the flush doesn't actually occur until VM-Enter, i.e.
the redundant flush is just an extra write to svm->vmcb->control.tlb_ctl (or an
extra decrement of asid_generation).