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kvm: nVMX: Remove unnecessary sync_roots from handle_invept

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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: bfd0a56b90 ("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>
This commit is contained in:
Jim Mattson 2019-06-13 09:16:08 -07:00 committed by Paolo Bonzini
parent 9824c83f92
commit b119019847
1 changed files with 4 additions and 6 deletions
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10
arch/x86/kvm/vmx/nested.c
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@ -4835,13 +4835,11 @@ static int handle_invept(struct kvm_vcpu *vcpu)
switch (type) {
case VMX_EPT_EXTENT_GLOBAL:
/*
* TODO: track mappings and invalidate
* single context requests appropriately
*/
case VMX_EPT_EXTENT_CONTEXT:
kvm_mmu_sync_roots(vcpu);
kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
/*
* TODO: Sync the necessary shadow EPT roots here, rather than
* at the next emulated VM-entry.
*/
break;
default:
BUG_ON(1);