On 22/02/19 17:46, Vitaly Kuznetsov wrote: > I noticed that fast_cr3_switch() always fails when we switch back from L2 > to L1 as it is not able to find a cached root. This is odd: host's CR3 > usually stays the same, we expect to always follow the fast path. Turns > out the problem is that page role is always mismatched because > kvm_mmu_get_page() filters out cr4_pae when direct, the value is stored > in page header and later compared with new_role in cached_root_available(). > As cr4_pae is always set in long mode prev_roots cache is dysfunctional. Really cr4_pae means "are the PTEs 8 bytes". So I think your patch is correct but on top we should set it to 1 (not zero!!) for kvm_calc_shadow_ept_root_page_role, init_kvm_nested_mmu and kvm_calc_tdp_mmu_root_page_role. Or maybe everything breaks with that change. > - Do not clear cr4_pae in kvm_mmu_get_page() and check direct on call sites > (detect_write_misaligned(), get_written_sptes()). These only run with shadow page tables, by the way. Paolo
