• Jim Mattson's avatar
    kvm: nVMX: Remove unnecessary sync_roots from handle_invept · b1190198
    Jim Mattson authored
    When L0 is executing handle_invept(), the TDP MMU is active. Emulating
    an L1 INVEPT does require synchronizing the appropriate shadow EPT
    root(s), but a call to kvm_mmu_sync_roots in this context won't do
    that. Similarly, the hardware TLB and paging-structure-cache entries
    associated with the appropriate shadow EPT root(s) must be flushed,
    but requesting a TLB_FLUSH from this context won't do that either.
    
    How did this ever work? KVM always does a sync_roots and TLB flush (in
    the correct context) when transitioning from L1 to L2. That isn't the
    best choice for nested VM performance, but it effectively papers over
    the mistakes here.
    
    Remove the unnecessary operations and leave a comment to try to do
    better in the future.
    Reported-by: default avatarJunaid Shahid <junaids@google.com>
    Fixes: bfd0a56b ("nEPT: Nested INVEPT")
    Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
    Cc: Nadav Har'El <nyh@il.ibm.com>
    Cc: Jun Nakajima <jun.nakajima@intel.com>
    Cc: Xinhao Xu <xinhao.xu@intel.com>
    Cc: Yang Zhang <yang.z.zhang@Intel.com>
    Cc: Gleb Natapov <gleb@redhat.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Reviewed-by Peter Shier <pshier@google.com>
    Reviewed-by: default avatarJunaid Shahid <junaids@google.com>
    Signed-off-by: default avatarJim Mattson <jmattson@google.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    b1190198
nested.c 180 KB