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

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jan,

On 15/05/2017 09:08, Jan Beulich wrote:
> > > > On 12.05.17 at 19:01, <blackskygg@xxxxxxxxx> wrote:
> > ====================================================
> > 1. Motivation and Description
> > ====================================================
> > Virtual machines use grant table hypercalls to setup a share page for
> > inter-VMs communications. These hypercalls are used by all PV
> > protocols today. However, very simple guests, such as baremetal
> > applications, might not have the infrastructure to handle the grant table.
> > This project is about setting up several shared memory areas for inter-VMs
> > communications directly from the VM config file.
> > So that the guest kernel doesn't have to have grant table support to be
> > able to communicate with other guests.
> I think it would help to compare your proposal with the alternative of
> adding grant table infrastructure to such environments (which I
> wouldn't expect to be all that difficult). After all introduction of a
> (seemingly) redundant mechanism comes at the price of extra /
> duplicate code in the tool stack and maybe even in the hypervisor.
> Hence there needs to be a meaningfully higher gain than price here.
This is a key feature for embedded because they want to be able to share 
buffer very easily at domain creation time between two guests.
Adding the grant table driver in the guest OS as a high a cost when the 
goal is to run unmodified OS in a VM. This is achievable on ARM if you 
use passthrough.
Cheers,

--
Julien Grall

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