KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE

Explicitly check for a REMOVED leaf SPTE prior to attempting to map
the final SPTE when handling a TDP MMU fault.  Functionally, this is a
nop as tdp_mmu_set_spte_atomic() will eventually detect the frozen SPTE.
Pre-checking for a REMOVED SPTE is a minor optmization, but the real goal
is to allow tdp_mmu_set_spte_atomic() to have an invariant that the "old"
SPTE is never a REMOVED SPTE.

Signed-off-by: Sean Christopherson <[email protected]>
Reviewed-by: Ben Gardon <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 3751a33ee258..cd6ceca5f2ba 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1193,7 +1193,11 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		}
 	}
 
-	if (iter.level != fault->goal_level) {
+	/*
+	 * Force the guest to retry the access if the upper level SPTEs aren't
+	 * in place, or if the target leaf SPTE is frozen by another CPU.
+	 */
+	if (iter.level != fault->goal_level || is_removed_spte(iter.old_spte)) {
 		rcu_read_unlock();
 		return RET_PF_RETRY;
 	}