KVM: x86/mmu: WARN if KVM attempts to map into an invalid TDP MMU root

When mapping into the TDP MMU, WARN (if KVM_PROVE_MMU=y) if the root is
invalid, e.g. if KVM is attempting to insert a mapping without checking if
the information and MMU context is fresh.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/mmu/tdp_mmu.c

@@ -1273,6 +1273,8 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	struct kvm_mmu_page *sp;
 	int ret = RET_PF_RETRY;
 
+	KVM_MMU_WARN_ON(!root || root->role.invalid);
+
 	kvm_mmu_hugepage_adjust(vcpu, fault);
 
 	trace_kvm_mmu_spte_requested(fault);