Re: [RFC v2]Proposal to allow setting up shared memory areas between VMs from xl config file

[Julien Grall <julien.grall@arm.com>]

Hi,

On 22/06/17 22:05, Stefano Stabellini wrote:
>> When we encounter an id IDx during "xl create":
>>
>>   + If it’s not under /local/shared_mem:
>>     + If the corresponding entry has a "master" tag, create the
>>       corresponding entries for IDx in xenstore
>>     + If there isn't a "master" tag, say error.
>>
>>   + If it’s found under /local/shared_mem:
>>     + If the corresponding entry has a "master" tag, say error
>>     + If there isn't a "master" tag, map the pages to the newly
>>       created domain, and add the current domain and necessary information
>>       under /local/shared_mem/IDx/slaves.
>
> Aside from using "gfn" instead of gmfn everywhere, I think it looks
> pretty good.
>
> I would leave out permissions and cacheability attributes from this
> version of the work. I would just add a note saying that memory will be
> mapped as RW regular cacheable RAM. Other permissions and cacheability
> will be possible, but they are not implemented yet.

Well, I think we should design the interface correctly from the 
beginning to facilitate future extension.

Also, you need to clarify what you mean by "regular cacheable RAM". Are 
they write-through, write-back...? But, on ARM, this would only be the 
caching attribute in stage-2 page table. The final caching, memory type, 
shareability would be a combination of stage-2 and stage-1 attributes.

Cheers,

-- 
Julien Grall

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