On 15/02/2023 23:16, Sean Christopherson wrote: > On Tue, Feb 14, 2023, Jeremi Piotrowski wrote: >> On 13/02/2023 20:56, Paolo Bonzini wrote: >>> On Mon, Feb 13, 2023 at 8:12 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: >>>>> Depending on the performance results of adding the hypercall to >>>>> svm_flush_tlb_current, the fix could indeed be to just disable usage of >>>>> HV_X64_NESTED_ENLIGHTENED_TLB. >>>> >>>> Minus making nested SVM (L3) mutually exclusive, I believe this will do the trick: >>>> >>>> + /* blah blah blah */ >>>> + hv_flush_tlb_current(vcpu); >>>> + >>> >>> Yes, it's either this or disabling the feature. >>> >>> Paolo >> >> Combining the two sub-threads: both of the suggestions: >> >> a) adding a hyperv_flush_guest_mapping(__pa(root->spt) after kvm_tdp_mmu_get_vcpu_root_hpa's call to tdp_mmu_alloc_sp() >> b) adding a hyperv_flush_guest_mapping(vcpu->arch.mmu->root.hpa) to svm_flush_tlb_current() >> >> appear to work in my test case (L2 vm startup until panic due to missing rootfs). >> >> But in both these cases (and also when I completely disable HV_X64_NESTED_ENLIGHTENED_TLB) >> the runtime of an iteration of the test is noticeably longer compared to tdp_mmu=0. > > Hmm, what is test doing? Booting through OVMF and kernel with no rootfs provided, and panic=-1 specified on the kernel command line. It's a pure startup time test. > >> So in terms of performance the ranking is (fastest to slowest): >> 1. tdp_mmu=0 + enlightened TLB >> 2. tdp_mmu=0 + no enlightened TLB >> 3. tdp_mmu=1 (enlightened TLB makes minimal difference)
