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Re: [Xen-devel] Proposal to allow setting up shared memory areas between VMs from xl config file

On Wed, 24 May 2017, Zhongze Liu wrote:
> Hi there,
> Thanks for your comments. They are all very insightful.
> Having read through the discussions so far, I can draw the
> following conclusions:
> 0. The syntax and semantics of the new config option should be more clearlly
>     defined. And this actually depends on the following:
> 1. If we're going to make this project arch-neutral, then the manifestation
>     of the frame numbers should also be arch-neutral;
> 2. Attributes such as readability, writability (and maybe even
>     cacheability and shareability) should be able to be specified in the
>     config files
> 3. We should allow users to specify the mfn of the shared pages as well. (but
>     I think maybe we could just specify a memory zone (if we're dealing
>     with NUMA) instead of a specific physical address).
> 4. (maybe in the future) Set up a notification channel between domains
>     who are communicating through shared memory regions. The
>    channel could be built upon PPI or SGI.
> 5. Clearify the ownership of shared pages, and thus the creation order.
>     I thinks I've already clearify this in my proposal -- we just
> treat the first domain
>     created with the shared memory range as the owner.
>     But specifying  this in the config file also makes sense. Then we'll have 
> to
>     enforced that the owner is created prior to all the "clients".

Right, I think we have to be explicit about this to avoid scenarios
where it is not known deterministically which domain is created first.
Imagine if the user gets the idea of doing:

  xl create dom1 &
  xl create dom2 &

> After talking to stefano, I'll try to first come out with a tiny but
> working prototype
> and do some evaluations on it. I'll not fully deny the possibility of using
> the grants api as the final implementation choice.
> This list might be incomplete. Please tell me if I missed or misunderstand any
> important information.

Thanks Zhongze!

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