Re: kvm_mmu doubts

[Avi Kivity <avi@qumranet.com>]

Sukanto Ghosh wrote:
>> Sukanto Ghosh wrote:
>>     
>>> What do these refer to ?
>>> i) kvm_rmap_desc
>>>       
>> It's a reverse mapping listing all shadow ptes pointing to a given guest
>>     
> page.
>   
> Then what is the rmap field of the 'struct kvm_memory_slot' ? Is it the
> list of kvm_rmap_desc (one list entry for each guest page in that memory
> slot) ?
>
>
>   

The head of this list.

>>> iii) kvm_mmu_page-> spt ??? ( i thought kvm_mmu_page itself refers to page
>>> of shadow PT, then what does spt points to ? )
>>>       
>> kvm_mmu_page contains information about the guest page table and the
>>     
> host shadow page table.  spt is the host shadow page table.
>   
>
> I got more confused now.
> I think it is due to terminology. I am novice here and I try to relate
> everything to the OS textbooks.
>
>   

Well, that won't work as I haven't read those textbooks.

> I am calling the entire tree-like structure (including the page
> directories) as a page table. In the above statement are you referring to
> the same ? Or is it the last-level table that holds translated physical
> addresses (+ dirty  bit, etc ) ?
>   

No, any guest page that is part of the structure. Note the structure is 
not a tree, since multiple roots exist and as it may be cyclic.

> What about the PGD, PMDs ?
>   

We try not to use Linux specific names while describing guests.

> Also, can you explain a line about each of these fields of the
> kvm_mmu_page:
>
> i) link (LRU link of what ?)
>   

Yes, the lru link.

> ii) gfn (guest frame number of the guest page table ?)
>   

Yes.

> iii) parent_pte (in a multi-level page table structure, the PTE in a page
> directory that holds the base address of the page table)
>   

Yes (or a list of those pte pointers).

> iv) root_count ( comment says 'currently serving as an active root; .is
> root = PGD? )
>   

Yes.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.