Re: [PATCH 18/22] kvm: mmu: Support disabling dirty logging for the tdp MMU

[Paolo Bonzini]

On 07/10/20 18:30, Ben Gardon wrote:
>> I'm starting to wonder if another iterator like
>> for_each_tdp_leaf_pte_root would be clearer, since this idiom repeats
>> itself quite often.  The tdp_iter_next_leaf function would be easily
>> implemented as
>>
>>         while (likely(iter->valid) &&
>>                (!is_shadow_present_pte(iter.old_spte) ||
>>                 is_last_spte(iter.old_spte, iter.level))
>>                 tdp_iter_next(iter);
> Do you see a substantial efficiency difference between adding a
> tdp_iter_next_leaf and building on for_each_tdp_pte_using_root with
> something like:
> 
> #define for_each_tdp_leaf_pte_using_root(_iter, _root, _start, _end)    \
>         for_each_tdp_pte_using_root(_iter, _root, _start, _end)         \
>                 if (!is_shadow_present_pte(_iter.old_spte) ||           \
>                     !is_last_spte(_iter.old_spte, _iter.level))         \
>                         continue;                                       \
>                 else
> 
> I agree that putting those checks in a wrapper makes the code more concise.
> 

No, that would be just another way to write the same thing.  That said,
making the iteration API more complicated also has disadvantages because
if get a Cartesian explosion of changes.

Regarding the naming, I'm leaning towards

    tdp_root_for_each_pte
    tdp_vcpu_for_each_pte

which is shorter than the version with "using" and still clarifies that
"root" and "vcpu" are the thing that the iteration works on.

Paolo