[PATCH v3 23/28] KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE

Sean Christopherson
2022-02-26T00:18:04Z

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>
---
arch/x86/kvm/mmu/tdp_mmu.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 4151e61245a7..1acd12bf309f 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1250,7 +1250,11 @@ 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;
}
--
2.35.1.574.g5d30c73bfb-goog