KVM: x86/mmu: Assert on @mmu in the __kvm_mmu_invalidate_addr()

Add assertion to track that "mmu == vcpu->arch.mmu" is always true in the
context of __kvm_mmu_invalidate_addr(). for_each_shadow_entry_using_root()
and kvm_sync_spte() operate on vcpu->arch.mmu, but the only reason that
doesn't cause explosions is because handle_invept() frees roots instead of
doing a manual invalidation.  As of now, there are no major roadblocks
to switching INVEPT emulation over to use kvm_mmu_invalidate_addr().
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Like Xu <likexu@tencent.com>
Link: https://lore.kernel.org/r/20230523032947.60041-1-likexu@tencent.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/mmu/mmu.c

@@ -5797,6 +5797,14 @@ static void __kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu
 
 	vcpu_clear_mmio_info(vcpu, addr);
 
+	/*
+	 * Walking and synchronizing SPTEs both assume they are operating in
+	 * the context of the current MMU, and would need to be reworked if
+	 * this is ever used to sync the guest_mmu, e.g. to emulate INVEPT.
+	 */
+	if (WARN_ON_ONCE(mmu != vcpu->arch.mmu))
+		return;
+
 	if (!VALID_PAGE(root_hpa))
 		return;