Re: [PATCH v4 07/30] KVM: x86/mmu: do not allow readers to acquire references to invalid roots

[Sean Christopherson]

On Thu, Mar 03, 2022, Paolo Bonzini wrote:
> Remove the "shared" argument of for_each_tdp_mmu_root_yield_safe, thus ensuring
> that readers do not ever acquire a reference to an invalid root.  After this
> patch, all readers except kvm_tdp_mmu_zap_invalidated_roots() treat
> refcount=0/valid, refcount=0/invalid and refcount=1/invalid in exactly the
> same way.  kvm_tdp_mmu_zap_invalidated_roots() is different but it also
> does not acquire a reference to the invalid root, and it cannot see
> refcount=0/invalid because it is guaranteed to run after
> kvm_tdp_mmu_invalidate_all_roots().
> 
> Opportunistically add a lockdep assertion to the yield-safe iterator.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---

Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>