On Fri, Mar 04, 2022, Paolo Bonzini wrote: > On 3/3/22 22:32, Sean Christopherson wrote: > I didn't remove the paragraph from the commit message, but I think it's > unnecessary now. The workqueue is flushed in kvm_mmu_zap_all_fast() and > kvm_mmu_uninit_tdp_mmu(), unlike the buggy patch, so it doesn't need to take > a reference to the VM. > > I think I don't even need to check kvm->users_count in the defunct root > case, as long as kvm_mmu_uninit_tdp_mmu() flushes and destroys the workqueue > before it checks that the lists are empty. Yes, that should work. IIRC, the WARN_ONs will tell us/you quite quickly if we're wrong :-) mmu_notifier_unregister() will call the "slow" kvm_mmu_zap_all() and thus ensure all non-root pages zapped, but "leaking" a worker will trigger the WARN_ON that there are no roots on the list.
