[PATCH 06/17] KVM: x86/tdp_mmu: Morph the !is_frozen_spte() check into a KVM_MMU_WARN_ON()

[Rick Edgecombe]

Remove the conditional logic for handling the setting of mirror EPTs to
frozen in __tdp_mmu_set_spte_atomic() and add it as a warning instead.

Mirror TDP needs propagate PTE changes to the to the external TDP. This
presents a problem for atomic updates which can't update both at once. So
a special value, FROZEN_SPTE, is used as a temporary state during these
updates to prevent concurrent operations to the PTE. If the TDP MMU tried
to install this as a long term value, it would confuse these updates.
Despite this __tdp_mmu_set_spte_atomic() includes a check to handle it
being set. Remove this check and turn it into a warning.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 0809fe8e8737..338957bc5109 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -656,7 +656,13 @@ static inline int __must_check __tdp_mmu_set_spte_atomic(struct kvm *kvm,
 	 */
 	WARN_ON_ONCE(iter->yielded || is_frozen_spte(iter->old_spte));
 
-	if (is_mirror_sptep(iter->sptep) && !is_frozen_spte(new_spte)) {
+	/*
+	 * FROZEN_SPTE is a temporary state and should never be set via higher
+	 * level helpers.
+	 */
+	KVM_MMU_WARN_ON(is_frozen_spte(new_spte));
+
+	if (is_mirror_sptep(iter->sptep)) {
 		int ret;
 
 		ret = set_external_spte_present(kvm, iter->sptep, iter->gfn,
-- 
2.53.0