Re: [PATCH v2 2/2] Xen: Document the semantic of the pagetable_reserve PVOPS

[Attilio Rao <attilio.rao@citrix.com>]

On 14/08/12 14:57, David Vrabel wrote:
> On 14/08/12 13:24, Attilio Rao wrote:
>    
>> The informations added on the hook are:
>> - Native behaviour
>> - Xen specific behaviour
>> - Logic behind the Xen specific behaviour
>>      
> These are implementation details and should be documented with the
> implementations (if necessary).
>    

In this specific case, implementation details are very valuable to 
understand the semantic of operations, this is why I added them there. I 
think, at least for this case, this is the best trade-off.

>> - PVOPS semantic
>>      
> This is the interesting stuff.
>
> This particular pvop seems a little odd really.  It might make more
> sense if it took a third parameter for pgt_buf_top.
>    

The thing is that this work (documenting PVOPS) should help in 
understanding the logic behind some PVOPS and possibly improve/rework 
them. For this stage, I agreed with Konrad to keep the changes as small 
as possible. Once the documentation about the semantic is in place we 
can think about ways to improve things more effectively (for example, in 
some cases we may want to rewrite the PVOP completely).

> "@pagetable_reserve is used to reserve a range of PFNs used for the
> kernel direct mapping page tables and cleans-up any PFNs that ended up
> not being used for the tables.
>
> It shall reserve the range (start, end] with memblock_reserve(). It
> shall prepare PFNs in the range (end, pgt_buf_top] for general (non page
> table) use.
>
> It shall only be called in init_memory_mapping() after the direct
> mapping tables have been constructed."
>
> Having said that, I couldn't immediately see where pages in (end,
> pgt_buf_top] was getting set RO.  Can you point me to where it's done?
>    

As mentioned in the comment, please look at xen_set_pte_init().

Attilio