Re: [PATCH v3 5/7] KVM: x86: Participate in bitmap-based PTE aging

[David Matlack]

On 2024-04-01 11:29 PM, James Houghton wrote:
> Only handle the TDP MMU case for now. In other cases, if a bitmap was
> not provided, fallback to the slowpath that takes mmu_lock, or, if a
> bitmap was provided, inform the caller that the bitmap is unreliable.

I think this patch will trigger a lockdep assert in

  kvm_tdp_mmu_age_gfn_range
    kvm_tdp_mmu_handle_gfn
      for_each_tdp_mmu_root
        __for_each_tdp_mmu_root
          kvm_lockdep_assert_mmu_lock_held

.. because it walks tdp_mmu_roots without holding mmu_lock.

Yu's patch[1] added a lockless walk to the TDP MMU. We'd need something
similar here and also update the comment above tdp_mmu_roots describing
how tdp_mmu_roots can be read locklessly.

[1] https://lore.kernel.org/kvmarm/ZItX64Bbx5vdjo9M@xxxxxxxxxx/