Re: [PATCH 4/7] kvm mmu: implement necessary data structures for second huge page accounting

Joerg Roedel
2009-03-29T13:32:32Z

On Sun, Mar 29, 2009 at 04:15:07PM +0300, Avi Kivity wrote:
> Joerg Roedel wrote:
>>>
>>>> +static int has_wrprotected_largepage(struct kvm *kvm, gfn_t gfn)
>>>> +{
>>>> + struct kvm_memory_slot *slot;
>>>> + int *hugepage_idx;
>>>> +
>>>> + gfn = unalias_gfn(kvm, gfn);
>>>> + slot = gfn_to_memslot_unaliased(kvm, gfn);
>>>> + if (slot) {
>>>> + hugepage_idx = slot_hugepage_idx(gfn, slot);
>>>>
>>> slot_largepage_idx() here?
>>>
>>> I don't think we ever write protect large pages, so why is this needed?
>>>
>>
>> For 2mb pages we need to check if there is a write-protected 4k page in it
>> before we map a 2mb page for writing. If there is any write-protected 4k
>> page in a 2mb area this 2mb page is considered write-protected. These
>> 'write-protected' 2mb pages are accounted in the account_shadow()
>> function. This information is taken into account when we decide if we
>> can map a guest 1gb page as a 1gb page on the host too.
>>
>
> account_shadowed() actually increments a hugepage write_count by 1 for
> every 4K page, not 2M page, if I read the code correctly. The code I
> commented on is right though.
>
> The naming is confusing. I suggest
> has_wrprotected_page_in_{large,huge}page(). although with the a level
> parameter we can keep has_wrprotected_page().

Yeah true, the name is a bit confusing. I think a level parameter for
has_wrprotected_page() is the best solution.

Joerg