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 <seanjc@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-24-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 3751a33..cd6ceca 100644 (file)
--- 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;
        }