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? > 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)
