Re: [PATCH 04/10] xen/arm: static memory initialization

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.05.2021 11:04, Penny Zheng wrote:
> Hi Jan
> 
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: Tuesday, May 18, 2021 6:43 PM
>> To: Penny Zheng <Penny.Zheng@xxxxxxx>
>> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
>> <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
>> sstabellini@xxxxxxxxxx; julien@xxxxxxx
>> Subject: Re: [PATCH 04/10] xen/arm: static memory initialization
>>
>> On 18.05.2021 11:51, Penny Zheng wrote:
>>>> From: Jan Beulich <jbeulich@xxxxxxxx>
>>>> Sent: Tuesday, May 18, 2021 3:16 PM
>>>>
>>>> On 18.05.2021 07:21, Penny Zheng wrote:
>>>>> This patch introduces static memory initialization, during system
>>>>> RAM boot
>>>> up.
>>>>>
>>>>> New func init_staticmem_pages is the equivalent of init_heap_pages,
>>>>> responsible for static memory initialization.
>>>>>
>>>>> Helper func free_staticmem_pages is the equivalent of
>>>>> free_heap_pages, to free nr_pfns pages of static memory.
>>>>> For each page, it includes the following steps:
>>>>> 1. change page state from in-use(also initialization state) to free
>>>>> state and grant PGC_reserved.
>>>>> 2. set its owner NULL and make sure this page is not a guest frame
>>>>> any more
>>>>
>>>> But isn't the goal (as per the previous patch) to associate such
>>>> pages with a _specific_ domain?
>>>>
>>>
>>> Free_staticmem_pages are alike free_heap_pages, are not used only for
>> initialization.
>>> Freeing used pages to unused are also included.
>>> Here, setting its owner NULL is to set owner in used field NULL.
>>
>> I'm afraid I still don't understand.
>>
> 
> When initializing heap, xen is using free_heap_pages to do the initialization.
> And also when normal domain get destroyed/rebooted, xen is using 
> free_domheap_pages,
> which calls free_heap_pages to free the pages.
> 
> So here, since free_staticmem_pages is the equivalent of the free_heap_pages 
> for static
> memory, I'm also considering both two scenarios here. And if it is domain get 
> destroyed/rebooted,
> Page state is in inuse state(PGC_inuse), and the page_info.v.inuse.domain is 
> holding the
> domain owner.
> When freeing then, we need to switch the page state to free state(PGC_free) 
> and set its inuse owner to NULL.

Perhaps my confusion comes from your earlier outline missing

3. re-associate the page with the domain (as represented in free
   pages)

The property of "designated for Dom<N>" should never go away, if I
understand the overall proposal correctly.

Jan