kvm: nVMX: Remove unnecessary sync_roots from handle_invept

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: Junaid Shahid <junaids@google.com>
Fixes: bfd0a56b90005f ("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: Junaid Shahid <junaids@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 509841916d232ba0f97d4a7037805a2fbaa7aed9..118d185764ec5ae95316dad2179785ca88754e3d 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4835,13 +4835,11 @@ static int handle_invept(struct kvm_vcpu *vcpu)
 
        switch (type) {
        case VMX_EPT_EXTENT_GLOBAL:
+       case VMX_EPT_EXTENT_CONTEXT:
        /*
-        * TODO: track mappings and invalidate
-        * single context requests appropriately
+        * TODO: Sync the necessary shadow EPT roots here, rather than
+        * at the next emulated VM-entry.
         */
-       case VMX_EPT_EXTENT_CONTEXT:
-               kvm_mmu_sync_roots(vcpu);
-               kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
                break;
        default:
                BUG_ON(1);