Re: [PATCH 10/28] KVM: x86/mmu: Allow yielding when zapping GFNs for defunct TDP MMU root

[Sean Christopherson]

On Tue, Dec 14, 2021, Sean Christopherson wrote:
> Assuming there is exactly one helper, that would also address my
> concerns with kvm_tdp_mmu_zap_invalidated_roots() being unsafe to call in parallel,
> e.g. two zappers processing an invalid root would both put the last reference to
> a root and trigger use-after-free of a different kind.

I take that back.  So long as both callers grabbed a reference to the root, multiple
instances are ok.  I forgot that kvm_tdp_mmu_zap_invalidated_roots() doesn't take
roots off the list directly, that's handled by kvm_tdp_mmu_put_root().